How Do I Query for Data Efficiently Using Contains() with Linq to Entities?

Efficiently Querying for Data with Contains() Using Linq to Entities

One common requirement in data access is to filter based on a list of values. The 'Contains()' method, available in many programming languages, simplifies this task. However, Linq to Entities, used with Microsoft's Entity Framework, lacked this functionality until recently.

Creating a Workaround using 'Any()'

Initially, an attempt was made to use the 'Any()' method as a workaround:

var q = from t in svc.OpenTransaction
        where txnIds.Any<long>(tt => tt == t.OpenTransactionId)
        select t;

However, this approach encountered an error due to the unsupported 'Any' method.

Supporting 'Contains()' in Entity Framework 4 and Up

Fortuitously, starting with Entity Framework 4, the 'Contains()' method is natively supported. This means that the following code can be used to filter based on a list of values:

var q = from t in svc.OpenTransaction
        where txnIds.Contains(t.OpenTransactionId)
        select t;

Using a Custom Extension Method for EF Versions Below 4

For EF versions prior to 4, a custom extension method can be implemented to provide a workaround for 'Contains()':

public static IQueryable<TEntity> WhereIn<TEntity, TValue>
  (
    this ObjectQuery<TEntity> query,
    Expression<Func<TEntity, TValue>> selector,
    IEnumerable<TValue> collection
  )
{
// ... Implementation goes here
}

Usage of the Custom Extension Method

To use the extension method, pass in the selector expression and the list of values to filter on:

var contacts = context.Contacts.WhereIn(c => c.Name, GetContactNames());

With this workaround, you can effectively filter data in Linq to Entities queries using Contains().

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