How to Implement \'Contains()\' Functionality in Linq to Entities?

Workaround for Implementing 'Contains()' Using Linq to Entities

The 'Contains()' method is not inherently supported by Linq to Entities, which poses a challenge when working with collections of IDs in a query. Here, we present a workable solution to address this limitation.

Solution:

To replace the unsupported 'Contains()' method, we leverage the 'Any()' method in its place:

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

However, this modification doesn't address the issue of 'Any()' not being supported in the context of Linq to Entities. To overcome this, we offer an alternative approach:

public static IQueryable<TEntity> WhereIn<TEntity, TValue>
(
this ObjectQuery<TEntity> query,
Expression<Func<TEntity, TValue>> selector,
IEnumerable<TValue> collection
)

This extension method enables you to apply a filter to a range of entity types and properties.

Usage Example:

The following code demonstrates how to utilize the 'WhereIn()' method:

using (MyObjectContext context = new MyObjectContext())
{
  //Using method 1 - collection provided as collection
  var contacts1 = context.Contacts.WhereIn(c => c.Name, GetContactNames());

  //Using method 2 - collection provided statically
  var contacts2 = context.Contacts.WhereIn(c => c.Name,
    "Contact1",
    "Contact2",
    "Contact3",
    "Contact4"
    );
}

By employing this solution, you gain the functionality of 'Contains()' while working with Linq to Entities, giving you greater flexibility in your queries.

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