---
title: NSExpressionDescription
framework: coredata
role: symbol
role_heading: Class
path: coredata/nsexpressiondescription
---

# NSExpressionDescription

An object that describes an expression to include with a fetch request.

## Declaration

```swift
class NSExpressionDescription
```

## Overview

Overview An expression description describes a value that a fetch request returns, which doesn’t appear as an attribute or relationship on an entity. For example, expressions can aggregate data, or  transform an attribute’s value. You add expression descriptions to a fetch request using the propertiesToFetch method. important: Don’t add expression descriptions to the properties array of NSEntityDescription.

## Topics

### Configuring the Expression Description

- [expression](coredata/nsexpressiondescription/expression.md)
- [resultType](coredata/nsexpressiondescription/resulttype.md)
- [expressionResultType](coredata/nsexpressiondescription/expressionresulttype.md)

### Deprecated

- [Deprecated Symbols](coredata/nsexpressiondescription-deprecated-symbols.md)

## Relationships

### Inherits From

- [NSPropertyDescription](coredata/nspropertydescription.md)

### Conforms To

- [CVarArg](swift/cvararg.md)
- [CustomDebugStringConvertible](swift/customdebugstringconvertible.md)
- [CustomStringConvertible](swift/customstringconvertible.md)
- [Equatable](swift/equatable.md)
- [Hashable](swift/hashable.md)
- [NSCoding](foundation/nscoding.md)
- [NSCopying](foundation/nscopying.md)
- [NSObjectProtocol](objectivec/nsobjectprotocol.md)

## See Also

### Specifying Fetch Constraints

- [predicate](coredata/nsfetchrequest/predicate.md)
- [fetchLimit](coredata/nsfetchrequest/fetchlimit.md)
- [fetchOffset](coredata/nsfetchrequest/fetchoffset.md)
- [fetchBatchSize](coredata/nsfetchrequest/fetchbatchsize.md)
- [affectedStores](coredata/nsfetchrequest/affectedstores.md)
- [NSFetchRequestExpression](coredata/nsfetchrequestexpression.md)
- [NSFetchedPropertyDescription](coredata/nsfetchedpropertydescription.md)