CreateIndex<T,TKey>(IObservableSource<T>,Expression<Func<T,TKey>>,Boolean,CultureInfo) Method

Creates a new index.

Syntax

Visual Basic
C#

'Declaration
 
Public Function CreateIndex
    (Of T,TKey)( _
   ByVal source As IObservableSource(Of T), _
   ByVal keySelector As System.Linq.Expressions.Expression(Of Func(Of T,TKey)), _
   ByVal keyIsUnique As System.Boolean, _
   ByVal locale As System.Globalization.CultureInfo _
) As Index(Of T,TKey)

public Index<T,TKey> CreateIndex<T,TKey>( 
   IObservableSource<T> source,
   System.Linq.Expressions.Expression<Func<T,TKey>> keySelector,
   System.bool keyIsUnique,
   System.Globalization.CultureInfo locale
)

Parameters

source: The collection to be indexed.
keySelector: Key selector expression of the index, see KeySelector.
keyIsUnique: Specifies whether the key used in this index is a unique key for the indexed collection.
locale: Locale information used to compare strings in the index (default: CultureInfo.CurrentCulture).

Type Parameters

T: The type of the elements of the collection to index.
TKey: The type of the index key.

Return Value

The new index.

Remarks

Normally, you don't need to use this method. Indexes are usually created in code by calling IndexCollection.Add, or their creation can be enforced in LINQ queries by using the Indexed hint. This method should be used only in special situations where all you want is to index a collection without an overhead of maintaining a collection of indexes, or you need an index that exists separately from the collection of indexes maintained by the source. Unlike the standard ways of creating indexes, this method only creates an index object and attaches it to the source (so it will be automatically synchronized with the source when the source is modified), but the created index is not added to IndexCollection<T>.

A unique index occupies less memory and performs better than a non-unique index (although the difference isn't dramatic). Therefore, for unique keys, it's recommended to specify the corresponding index as unique. But do that only if you are sure that the key is indeed unique, as it imposes a uniqueness constraint on the indexed collection. An attempt to modify the indexed collection violating the uniqueness throws an System.InvalidOperationException.

Requirements

Target Platforms: Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference

IndexingAlgorithm Class
IndexingAlgorithm Members