WWDC2004 Session 609

Transcript

Kind: captions Language: en good afternoon before I start I recognize a few faces in the audience can I see how many people have already done any web objects development before would you forgive me for asking the question why are you here this is an introductory session on learning to develop using web objects so if you've already done a few weeks worth of oil widgets development this is probably not the session for you if anybody wants to take the opportunity to find something more advanced to go to please do so now okay so what will we cover this is going to be for those of you who've been on any web watches programming classes about the equivalent of the first weeks worth of what objects programming class in about 55 minutes I wonder though if I might just ask if the clock has started yet just so I can count down so it's got to be necessarily a very rapid run-through we're not going to be able to go into any great deal of depth on the subject we're going to cover a little bit about what web objets is how you use it some of the basic design principles that you use with web objects as a technology some of the main features and some of the benefits that you get from using web objects in particular as we go through again to highlight some of the more useful aspects of the technology in some respects web objects is already doing and has been doing for some time what a number of other technologies are aiming to do in separating the business logic from the presentation layer what I want to do is illustrate some of that with demonstrations as we go through as I go through this presentation are a few things about making of you the sorts of things the sorts of technologies that web objects developers need to know about in order to be successful the technology are first of all Java it's possible to learn Java as you're developing and gaining experience with web objects who here just sort of interest then has not done any Java development before a few of you if you have a look on Apple's website you'll find a document Java for web objects developers many people have found that that's a very useful document for learning just enough Java to figure out how to use web objects it's actually quite a good introductory document just for learning Java itself it's also useful to know something about databases so why our database is useful how do you interact with them and so on and of course because there's a web-based development environment is useful to know about something about HTML as well as important in it as as any of these other technologies though to be successful with web objects you need an ability to think in terms of objects so this is a theme that I'm going to repeat again on a couple of occasions throughout for those of you who've come from a procedural background for those of you who are used to scripting and so on this may mark a fairly major paradigm shift for you a different way of thinking you'll find quite foreign so the common theme throughout is objects for the web what does a web objects provide for you where objects aims to give you a high degree of abstraction so we've got object representations of a number of the different state management entities and so on that you'll use during typical web development we therefore get all the benefits that you traditionally associated with object oriented design so reuse simplicity of concept and so on I want to emphasize that last point simplicity of concept one of the I'd like to suggest myths that's commonly associated with web objects is that it has a steep learning curve q Justice Steve Heymann therefore pointing out that the benefit of a steep learning curve is it means that you learn an awful lot in a short space of time what I would also like to suggest though is that many people find that web objects has a steep learning curve because they do not bring to the table the knowledge that I listed earlier is a set of prerequisites people who typically have difficulties with web objects are people who don't know Java don't know a thing about databases and don't know anything about HTML if you bring a knowledge of all those technologies to the table and think in terms of objects you'll have a much easier time so bear that in mind as you approach the technology another thing to bear in mind is that having done a lot of training courses using this technology in their past I've often noticed that people have a tendency to make things difficult for themselves if at any stage you find yourself struggling with a technology if you can't figure out how to get things connected if you can't figure out how to do something stop for a moment pause sit back think back to this session so take a moment just have a look around the room and familiarize yourself with this environment think back to here and think back to my voice on stage saying it's probably easier than you're making it you're thinking that it's more complicated than it really is often to do something complicated in webobjects takes a couple of lines of code the difficulty of course is figuring out what those couple of lines are so let's have a quick recap then on what web algae's is all about and in particular for those of you who might have been to one of the previous sessions or read a bit about the technology and so on what is web objects from a developer's perspective so as you sit here what will what use will you make you for the technology from a perspective that we're looking at it from today we're looking at web objects as a web development environment it's a set of tools and a set of four libraries for doing web based development as you're probably aware we're babji's is actually useful for creating other sorts of application as well so web services for example you can use it to create desktop based applications and so on but we're concentrating on its initial strengths here of building interactive dynamic websites the main strengths and the main reason that many people are interested in the technology is because it's particularly good at talking to databases so if you need to create a dynamic website website that talks to an Oracle database aside a they state abase or whatever webobjects gives you an excellent set of technologies for doing that it's also specially scalable so if you bear in mind it for example the iTunes music store uses web objects as a back-end technology that gives you an idea of how robust how scalable and so on this technology is it's been around for a long time so it's heritage goes back a decade or so in terms of weather widgets it's in many respects its can be considered as being middleware if we look to this report card when its main goals is to play well with others so it doesn't matter what web server you use it doesn't matter what database you use doesn't matter what HTML you want to produce and so on where Bob Jets fits in with the way that you want to work one of the advantages of this one particular benefits of this and the way the technology itself is structured is that it allows you to concentrate on that part of the application that you're most interested in as a developer you're probably most interested in the jar where the application logic it allows your database in device admins to concentrate on the database side of things and your graphic designers to concentrate on the HTML again from the developers perspective what tools do you use on a daily basis the main one that you're going to use it certainly on Mac OS 10 so there are other options for somebody's on other platforms on Mac OS 10 you'll use Xcode so the traditional Mac OS 10 development environment as you see who's not has anybody not used Xcode before okay so a couple of you but for the rest of you familiar territory where objects builder provides you with a graphical HTML editing tool you can use others but web objects builder we'll see in a moment obviously has particular strengths for dealing with some of the dynamic elements of web objects users yo modeler finally is our entity relational mapping tool so it's going to be the key to figuring out how stuff in the database gets into our application on screen some of the other things that we're Bob J's gives us as a as an entire package it gives us a collection of frameworks for providing object abstraction so most of the entities or things that we want to deal with as web developers in particular for representing dynamic web elements that's individual strings hyperlinks webpages and so on and for doing state management one of the frameworks that I'll just mention in passing here is the foundation framework who's done any cocoa development or heard of the foundation framework in cocoa for those of you again small number the there's a fairly strong correspondence between the foundation framework in cocoa and the foundation framework in web objects it provides you with a set of utility classes for representing number numbers dates dictionaries arrays and so on in addition there are a couple of other frameworks the web objects framework itself provides the object of structions for the dynamic elements and then there's a framework called the enterprise or a couple of frameworks that are bundled together and something called the enterprise object framework which actually interacts with a database for you so that's web objects in a nutshell from the developer's perspective in the remaining sections what I want to look at first of all some of the underlying design patterns that are going to be useful to you as web objects developers so some of the main ideas that underlie the technology then have a look in greater detail at some of the frameworks that you'll be using so what's in the fan what's in the web objects framework what's in the enterprise objects framework and see then particularly illustrated using demonstrations some other tasks your face on a day-to-day basis so turning first of all to the concepts to reiterate a point that I made of several occasions up until now then objects objects objects think in terms of objects many other tools that you may have used in the past will require you to think in procedural terms requires to do a lot of data munging or whatever to figure out what's going on in your application web objects is as the name implies object oriented so we have object abstractions for webpage and things on a web page that you could send messages to where you have object abstractions for records in the database so when you retrieve information the database you get objects representing the records even the HTTP requests and response are abstracted out into objects so for those of you who may in some environments be used to doing your own parsing or messing around with HTTP requests and response don't have to do that we'll see an illustration of that and very early on and then of course for state management so why are we interest in this state management again thinking about web objects as a traditional web development environment one of the things that many people want to get out of a web development or a web environment is some sort of state management if you're putting up a website particularly commercial websites these days you want to have an idea of a user so that a user has a shopping cart that they can put stuff into and later give you a credit card number that you can charge that you can earn some money and it's possibly not part of the traditional web development environment there you go so web objects provides you with state management abstractions for individual sessions for an individual user and then for an application and then at the the level of an individual page the design patterns the main ones that you need to bear in mind first of all model-view-controller has anybody who's heard of model-view-controller before okay this is going to be something if you go to many of the other sessions particularly the cocoa sessions for those of you who are interested you're going to get drummed into during the remainder of this week the idea fundamentally behind model of your controller is the separation of the factoring out of function as a name implies you have different sorts of objects in your applications model objects which typically correspond to records from the database view objects which in this which in our case are going to represent webpages or dynamic elements within a webpage and then a controller object which mediates the between the two the idea is that you should not pollute your model objects in particular with any knowledge of the user interface this makes them particularly reusable between applications similar story then with the view objects if a view object is not particularly bothered about what sort of data is presenting their reusable the controller is the glue code which sits between the two and typically that's unique to each individual application another important design pattern key value coding probably again familiar to some of you from the cocoa environment the idea behind key value coding is that it gives you a means of accessing and objects properties using the name of a property as a string so if a person has a first name property rather than using an accessive method or accessing an instance variable of that object directly you can use a message such as value for key and then passing a parameter first name as a string the main advantage of this is that this gives you very good flexibility at runtime you can determine at runtime what property of an object is that you want to access this is what gives web objects an awful lot of its flexibility another point to bear in mind here is that in addition to asking for just a single property you can follow what are known as key paths so if a person has a relationship to their manager and the manager then is another person who has a first name you can ask a person object for their managers first name by using the key path manager dot first-name so key value coding gives you means of traversing relationships the final design pattern that I want to draw your attention to here is one that's perhaps a little bit unexpected target action again anybody from the cocoa development environment or from any other development environment who's heard of target action before okay a very simple idea basically that when and certainly in a desktop application if you click a button a message is sent to whatever object you've connected it to what we'll see I think straight up very very early on is it with web objects you get a design a development environment it's very much like in many respects a desktop application development environment when you click on a button or a hyperlink you can cause an action method to message to be sent to an object to return to frameworks for those who haven't come across the jargon word framework before you can think of a framework as being pretty much like a class library collection of objects the main differences are a a framework may contain other resources so it may contain HTML that may contain documentation it may contain yo model files we'll talk about those later in addition one of the main things to that that may affect you as developers here is that programming using frameworks is philosophically rather different to some of the programming that you may have been used to if you use the procedural programming or scripting whatever typically you're used to being in charge at the top of your program you'll deal with getting information from the HTTP requests you'll do something with it at the end omit HTML perhaps or that might be the sort of development that you're used to in a framework based environment you're typically sitting back as a passive receiver of messages so and other things I've noticed in training is this can be quite discomforting for some people people don't or developers don't feel that they're in control of their application if you find yourself in that situation again sit back don't worry relax the reality is you're not in control but that's a good thing what again I hope we'll see very swiftly is that letting web objects take care of the heavy lifting frees you from all of that responsibility and allows you to concentrate on the more interesting things which would you rather deal with HTTP requests and responses or the actual application logic I suggest that the dealing with the application logic is going to certainly be a more productive way of using your time so turning first of all to the web objects framework and we're just gonna discuss it very little bit before going into a couple of demos remember that web objects the web budgets framework is the framework and that contains the object abstractions for the dynamic elements you'll have on a page a page itself and provide the state management classes the base method the route that I'm sorry that the base class for webpages and indeed for parts of webpages is woe component so as you create web pages or new web pages you're going to be creating new instances or new classes subclassed from wou component so let's illustrate that with the first demo so quick quick reminder here I'm not expecting here for everybody to go away being an expert web objects developer what I want you to get out of this is a flip flip feeling for what web objects development and is about what some of the typical processes are and so on so that subsequently if you want to take a look at the look at the product and start using it you can feel comfortable having seen somebody else do this and seeing that it's not particularly difficult so in project builder I'm going to start off by creating a new web object application that I'm going to inspiringly name hello whoa world and I'm not going to type it correctly and because this is a demo let's just ignore all these parts for the moment and go wind look at the default configuration so just out of the box project Xcode gives us a project that contains a lot of stuff let's just start off by building and running that to see what happens well it goes away builds runs and for your convenience it starts up and displays the webpage at the moment there's nothing in it that's probably unsurprising we haven't done anything what do we have to do to actually configure this and get something to display the page that we're seeing first of all is the main page so out of the box the project template provides us with a main component which comprises a number of different files including this main dot woh thing which is the template for the first page if I open that in web objects builder straightaway I hope you can see that where budgets builder is a graphical HTML editing tool into which I can type and if I build and run the application again since that's the first page that's displayed in the fullness of time I get the text but I wanted that's not particularly exciting I said that web obvious was it was a dynamic development environment so it's not particularly dynamic content let's suppose we want to at least display some semi dynamic content I can replace whoa world with a whoa string a whoa string is a dynamic element at runtime that string is going to be substituted by whatever value we associated with that string let's say oops that I want to add to my page a variable called user name to represent the user's name let's see what happens when I click Add here if I go to my Java code we'll see that I've got a class called main which is the object that underlies this page when it's generated that currently just has a constructor method when I say add once add some access of methods as well you'll see I get an instance variable added and suitable access and methods in web objects builder I also get user name added here as a variable from which I can drag this is now set the value for this string to be whatever username happens to be at runtime in my constructor let's say then I set that to be something not particularly dynamic oops and build and run the application I get some sort of dynamic content I'm going to pass on for the moment figuring out how we can actually get the user's name directly is going to come in the next session so let's for now see how can we get something a little bit more dynamic than that let's suppose we want to display the current time again we're going to use a wou string and add another key for current time in this case though this is one thing that just lot pause and think about for a moment in this case I'm only going to define and access a method this is an if add a read-only value I don't need to have an instance variable for this I just need a means of generating this value so I'm going to have a get method current time which is going to return an NS timestamp and I can connect that up and without going into too much detail here associate a date format with that so that specifies how this how the time is going to be represented on the page in my current time method then rather than returning an instance variable I'm going to return a new NS timestamp so when a new NS timestamp is created with no additional constructor arguments it'll be set to the current date and time so if I build that we actually do have some dynamic content I hope you'll agree that that was fairly straightforward in particular a couple of things to notice there we're sitting back being the passive recipient of messages so this illustrates the framework aspect we're actually doing anything very active in particular has anybody spotted where the HTTP requests an HTTP response come into this we haven't seen any hot hide or hair of them we're not bothered we can get to them if we want to but typically we don't have to I can still make this a little bit more dynamic without going into too much more detail at this stage let's suppose that rather than just displaying hello on the first page I want to display a hyperlink the hyperlink is going to take us to a new page hyperlink you might guess straight off is represented by an instance or a dynamic element woah hyperlink if I select in this toolbar I surround the text that I've selected with a hyperlink by clicking on the hyper hyperlink button a hyperlink is associated with an action so to my web page I'm going to add an action this time rather than a key the action method is going to be called go to welcome and it's going to take us to the Welcome page now this is important because I'm getting a step ahead of myself here deliberately I want to watch what happens when I add this here go - welcome gets added to the list of variables because web objects builder doesn't know any better at this stage I'm gonna specify that the action oops sorry the action associated with the hyperlink is go to welcome and save that and now I'm going to add the Welcome component to my project on this page I do want user name and it means of setting it because then to say welcome user name if you watched or if you're watching very carefully when I saved that go to welcome in Maine suddenly appeared bahut below a new line that's appeared web objects builder differentiates between variables in a page and action methods action methods appear below the line web objects is all that well we'll just builders figured out that welcome is actually a web objects component so a method that returns a web objects component page and takes no methods is counted as an action method notice in the action method that was added to the Java file I get a helpful hint here initialize your component if there's an initialization that I want to do I can do that after I created the instance of the page I'm about to go to so I can simply pass a variable to the next page thank you so again we get our sort of dynamic content click me and I get taken to the next page with some new information on it so that was a very quick run-through let's have a quick recap of what it was that we saw first of all actually let's just illustrate one other pink point here I sort of mentioned that a component comprises a number of different files there are three files that were primarily interested in in a web objects page first of all the HTML that defines the template for the page the Java is the under the Java file is the underlying business logic for that page and then there's a wad file the wad file is what defines the mapping between what's in the dynamic elements and what's in the code the main component is created by web objects automatically points to make about the HTML file firstly remember that web objects tries to play well with others just because you're using web objects does not mean that you can't use other web-based technologies as well so if you want to use CSS if you want to use JavaScript or whatever you can use those technologies and web widgets based application the only thing that's different about a web widgets page is it includes a web object a set of web budgets tags to represent the dynamic elements the dynamic elements that we've seen so far whoa string and whoa hyperlink later on we'll see were women he's got a collection of attributes each of which you can set graphically using web objects builder the Java file then is the business logic you can put whatever business whatever the instance variables you want into the page you can put whatever methods you want them to the page and so on the only difference about a sum of the page some similar methods is some methods may be action methods action methods have no arguments and return a subclass of an instance of a subclass of whoa component these are what you use for navigation the wad file then is a just simple text file and that binds the two together that specifies what attribute of the Java page corals is is used for what attribute such as the value for example of a string to go into some new areas then let's have a look at state management typically when you deal with a web-based application you're interested in managing users Co for an individual when a person comes to your website you want to keep track of them so you can find out what products are interested in buying and so on sometimes you need to maintain application wide state so where objects provides you with abstractions of both of these as you might expect from the names here a session represents the current user which you can access from a page using a static method session which simple returns of the current session whatever it happened whoever it happens to be says note so you don't have to do any work in figuring out who the current user is similar sort of thing with the application object if you wan to add States to the application Clark or object you can access the application object from any page using the application static method of the application class if you're dealing with dynamic content you typically need some means of retrieving information from the user so as you might expect from a web-based application we have abstractions for a form on a web page and text fields and so on it'll be able to retrieve information from that from the user we also have a submit button so wow so mitt button that you can use for it to allow the user to submit their information and again let's straighten that in a demonstration so going back to our previous application rather than just click me I want to add a form where I asked the user to add their name or tell us what their name is so I've added a whoa form to the page at is a text field and I'll have a submit button the submit button may as well go to go to welcome this time however I'm not going to collect that information on the current page username is probably something I want to collect a delivery application sorry I pick my level of a session so to my session class I'm going to add a key user name that's a string and bind the value of the text field to the sessions user name now as I have that I can rather happily remove code I don't now need to pass the user name from the first page the second moreover I don't now get into the user name from the second page that I'm going to I'm going to get it directly from the session so again build and run pretty straightforward I know that was quick you're probably I suspect that half of you go what did he just do there so reminder I've got to keep reminding myself this as well I'm not training you I'm giving you a feel for what the development environment is like I hope that either today or tomorrow you'll get a collection of all of these examples on the downloadable disk image so if you haven't been following just now you'll have the examples to have a look out later plus as a wealth of documentation already available online so where do we go from here if we have a look at a little bit more about some of the other dynamic elements that we can use there's a whole range of different dynamic elements that web objects provides you with so in addition just two strings hyperlinks and so on in particular a repetition to allow you to iterate over the contents of an array conditional to allow you to specify whether or not barring a dependence on what the current circumstances are a particular part of a web page gets displayed we have support for checkboxes radio buttons and so on and in particular then we have support for partial components so the main page that we've been created creating so far or the Welcome page could actually be sub parts of a page that we can reuse in different applications or in different apps or on different pages one of the more exciting ones in some respects is the woe component content which I add you to have a look at let's some stage which can represent the template for a page so we actually have done dynamic templates for our pages as well the only one I want to have a look at just for now is the whoa repetition to illustrate how that can be used to iterate over the contents of an array in again another demo this time starting with an existing project so in this project I've already defined a session class that creates for me an array of person objects in my first page I want to display their list of all of the people in that array and I'll do that by adding a whoa repetition which will iterate over all of the people in that array to be able to iterate over those I need a variable which will be set to each of those in turn and that's going to be a variable of type person as you don't need access and methods so for each person in turn I want to display their full name your build and run that application then for some reason there's a permissions problem actually no which I had checked beforehand of it there you go tips let's try that again so I get a list of all of the people in the array that's not particularly exciting by itself how about allowing the user to select one of those I can surround the person's name or each person's name with a hyperlink to just remind myself select a person so the action method that will be invoked when the user clicks on the hyperlink is select person what that will do is go to the next page is going to be selection and pass current person as a selected person the selection page you can probably imagine is going to display the name of the selected person so I'm passing information from one page to the next so dealing with iterations or repetitions within web objects turns out to be very simple if you think in terms of objects final thing just to add here to add a little bit of substance to it let's add the ability to display a graphic so another access a method that's a read-only value that simply returns the person's name with the suffix jpg which I can then bind to the file name of a wou image in the resources for my project I've got a series of images so when I select an individual I can see their picture and so on so I hope you're getting the feeling from this already that it's a fairly easy development environment in particular very interactive so there's not a big there's not a big turnaround time you can very quickly see the results of what it is that you're doing the final thing that I want to come on to is what many people regard as the crown jewels of this technology the database access layer database access as I mention is mediated through the enterprise objects framework AOF as perhaps sometimes confusingly its referred to is the collection of objects that mediate between what's in the database and the objects in your application so loosely speaking you can say that a record or a row in your database is going to correspond to an object in your application in your database you have tables and either records or rows depending on the terminology in your application you have classes and instances of classes VOF is what map's the two things together typically you're dealing at a high level of abstraction one thing I want to re-emphasize here and something that applies throughout web objects is that even though you're using typically a high level of that FF abstraction you are not precluded from using lower level details should you wish to do so so if I unwrap the double negative there even though you're using web objects you can still use raw sequel if you want you can still use JDBC you can still get at the header the HTTP header information and so on if you want to if you feel that you need to the other vital thing about AOF is that it provides a great degree of management for you I said loosely speaking an object in your application corresponds to a record in the database or vice versa and because if I simply say that a record in the database corresponds to an object in your application there's a temptation to think from that that your entire database is going to end up in memory that is not the case one of the things that the AF is particularly good at that those of you who anybody go to the core data presentation just now when andreas spoke just now about faulting the same technology applies to EOF you only retrieve into memory using EOF those records that you actually need so if you're collecting all of the purse or a selection of persons from a person table in your database you only get enterprise objects created for those persons that you retrieve if a person has a relationship to a department until such time as you ask a person for the department to which they belong the department record is not fetch from the database so AOF puts bounds for you on the object graph that you create in particular we'll see illustrated in a couple of slides time eyo F also manages relationships between objects for you how many people do database access who uses sequel here ok so you're probably familiar with the concepts of primary key foreign key and so on we'll see that the way that relationships that were represented in objects is very different to the way they represented in a database and EF needs to do some extra work for you how does it do its work well again for those of you who are at Andreas's session it relies ultimately on a model of the key parts of developing your application is it's at the outset you should create an ER model that defines the mapping between what's in your application what's in the database you can also create custom classes to represent your data objects you don't have to if you don't want to EF provides for you a neo generic record class which is able to represent any sort of entity typically however in order to add value you'll do some customization it also then provides you with a whole infrastructure for actually accessing the database for making changes to objects and then saving those changes back to the database should you wish ultimately as I mentioned though everything is basically founded upon the EO model the ER model you edit graphically using the ER model a tool which I'm not going to demonstrate now right so the picture should show you that basically is an entity relationship modeling tool with it you can specify class what class in your application is going to be used to represent what table in your database and what columns in a given table are going to be used as instance variables in a given class moreover you specify what the primary key is or the primary keys are for any given entity and what their what variables are actually going to represent in a class so if you've got a collection so so for example you don't have to use all of the columns from a given from a given table if you don't want to in your application your classes are that your database rows or records are represented by instances of enterprise objects so we have yo jennette record and I mention on an earlier slide our custom object yo generic record is rather like a date addiction rates capable of representing any sort of entity as a historical footnote it happens to inherit from yo custom object in in your applications you'll typically just subclass yo generic record should you wish to do so in a subclass you can add whatever custom logic whatever behavior you want again for those of you who are at Andreas this session this corresponds to an s managed object in core data some of the behavior that you might want to add may be very straightforward if we have a person class it may be that you simply want to have a consistent means of representing a person's full name so a bit of custom logic would simply be to implement a full name method which returns a catenation of first name and last name if you want to edit enterprise objects thinking back to what I said about weblog just as a technology as a whole you're just been dealing with objects what do you want what do you do when you want to edit at any other object in Java simply send a message if you remember also what I said about key value coding you can edit a given Enterprise object by simply sending using key value coding methods such as take value for key so you pass in as arguments to take value for key method the new value and the name of the attribute that you want to change as a string or if you've implemented your own custom subclasses of energy our egg record which have custom access and methods defined you simply call other relevant access and Method an important point here is that a similar sort of thing works when you're manipulating relationships as when you're manipulating straightforward attributes where objects even handles many to many relationships for you for that so for the DBAs amongst you who had to deal with join tables up until now you do not have to deal with join tables using the AF it's all handled for you for you prove Yuda specify the model correctly so if you're using if you have a relationship say between a movie entity and a studio entity and you want to set the movie so it's the studio to which a movie belongs if you had a custom subclass of a generic record you might simply send a set studio message to give an instance of a movie class of a movie or the movie class there's a little bit extra work that you might have to do if you have too many relationships for too many relationship to set the movies for a given studio you might have a custom methods add to and then name of relationship and remove from named relationship one of the issues here though relates back to the issue that I mentioned about the way that relationships are represented in object versus the way that they're represented in your database if you remember in a database a relationship is modeled by having a foreign key in a table in the object world things are a little bit different with objects we have references whether it be directly to an instance of the destination of the relationship or a reference to an array that contains a collection of instances of the destination for a relationship therefore if we want to assign in this example an employee to a different department our employee Jackson happens currently to belong to the events department if we simply tell Jackson that you're now in sales if you think about this in terms of the real world if all that we do is tell Jackson his current department doesn't know that he's been reassigned moreover the new department is going to doesn't know that he's being reassigned we have to explicitly mattel each of the two departments about the move it's a similar thing in objects on the database all that we will do is change Jackson that their foreign key in a table in objects we have to be more explicit and actually send messages to the other two departments if I go back one of things that I skipped over at the end of this slide was it is actually a rather long method name and object to both sides of the relationship with key which it first is rather intimidating when you start using well objects you'll learn to like it because what it does is it manages all of this stuff for you so for those of you who are DBAs or have dealt with databases in the past this is a fairly high degree of abstraction you don't have to worry about primary keys you don't have to worry about foreign keys you don't have to worry about maintenance of relationship integrity of relationships EF manages all of that for you a lot of that's managed for you by the editing context the editing context is can be thought of basically as a sort of scratch pad it's the object that mediates between you and the underlying connection to the database so it's the object that you turn to when you want to fetch stuff from the database and safe and safe stuff back to the database it also observes all of the objects you've retrieved from the database looks for changes to them and then in particular allows you to undo those changes should you wish you can get hold of it then add in contacts right each session as you might expect so every users wants to have their own collection of products that they're buying in their own shopping cart and so on each session comes along with their own its own default editing context that you typically turn to when you want to do something like fetch information from the database so to fetch information from the database you have to specify what it is that you're after you specify it using an object again known as a fetch specification sending a message objects with specification to the editing context returns to you an array of enterprise objects that match the filter that you set for that specific specification so let's suppose we have our database full of movie information we can ask an editing context to ask the database through the intervening objects in ef4 for example all of the movies whose title big contains the word Nemo we might also add that we want to have the objects returned sorted by title so we simply send a message objects the Fest pacification past the parameter this fetch specification that we specified to the editing context it returns then a collection of objects the fetch specification itself contains in for all the information that a of' requires to determine what's going to be got from database minimally we must specify the name of the entity so what table is in effect that we're interested in we might also want to narrow our search so maybe we would say as in this case we're only interested in movies whose title contains the word Nemo if we don't specify a qualifier we'll get back everything from that table we might also specify an array of sort ordering so we may won't want to get the movies back order first of all by title then by revenue then by studio or whatever so as an example a bit of code this bit of code is a little bit dense so apologies for that but this bit of code basically does all of that for us so first of all get hold of an editing context in the first line create a new qualifier create a new set of sort or rings it and it contains a single sort ordering here and then create our new face specification object and send that to our editing context so didn't give you very long to have a look at that but I've got a prepackaged demo that does that you'll notice that I've already gotten the Oh model in my application so I've already set up a repetition it's going to iterate over a collection of movies one at a time and display the name of the studio in this case that I'm interested in for no particular reason if I have a look at the code the code is basically the same as in essence the code that I just displayed except in this case because the database if I happen to be using doesn't contain Nemo anywhere and we're going to be looking for studios named or movies from studios named MGM there's a subtle point here which I'll come back to in a moment and I'm going to get hold of the editing context create a qualifier create a set of sort orderings f8 specification and then use that fetch specification this again I'm sorry this is rather tiresome there's gonna be more kind thank you that's more interesting still now I'm going to guess that this has something to do with some of the another setup that was done after I set my stuff up what's happening is that for some reason I can't actually connect to the database and I suspect that it has something to do with the IP setup and it was done afterwards such is life and I don't think that there's anything that I can quickly do to rectify that which is shall we say unfortunate and I'm guessing from the lack of responses there that that's the answer so I hope you will forgive me that's going to be even less impressive a demo than we might have expected if you could imagine that rather than a collection of error messages this webpage displayed a list of all of the movies that we'd fetched I hope you might agree that had it worked this is actually not very many lines of code to go to a database fetch some information and collect a series of records back from the database the subtle point that I wanted to make here that I said I was just glossing over a little bit was notice that in our qualifier which specified that we were interested in the studio name for the movies so rather than just searching by title which is searching within the single table that we were interested in we're actually traversing a relationship here so we're traversing the relationship from a movie to the studio to which that movie belongs and looking to see what what the name is of that studio so very easily which reversing relationships in this query as well not particularly difficult so for those of you who have used other environments particularly anybody here used EJB anybody care to do a coat light lines of code comparison between what we should have achieved here had the database connection been up and what you would had to do an EJB fewer lines of code here at least I'm going if honestly there's somebody nodding in the front row so with that I said it was going to be a very very quick run-through the goal here was just to give you some sort of a taste of what it's like to do web objects development and as you can see there's occasional frustrations with it but I hope that you might also see that it compared with some environments that you're used to it's actually quite fluid very responsive and in particular there's not a lot of not many lines of code to actually achieve quite an interesting result the examples that I've been through I will get up on the connector a whole calm sight as quickly as possible after this session it may be tomorrow evening that it goes up in the interim though there's plenty of documentation available online so we're all jizz is very thoroughly documented basically the main place that I would suggest that you start with is the aptly named getting started page