Why does the Contains() operator degrade Entity Framework' Linq queries?

Question

I read here that in entity framework if you perform contains operation it reduces performance:

Contains is converted to \"WHERE IN\" in SQL which cause pe

Answer 1

Yes Contains() will degrade performance heavily.

So You can try below mentioned solution.

We were able to solve the EF Contains problem by adding an intermediate table and joining on that table from LINQ query that needed to use Contains clause. We were able to get amazing results with this approach. We have a large EF model and as "Contains" is not allowed when pre-compiling EF queries we were getting very poor performance for queries that use "Contains" clause.

An overview:

1. Create a table in SQL Server - for example HelperForContainsOfIntType with HelperID of Guid data-type and ReferenceID of int data-type columns. Create different tables with ReferenceID of differing data-types as needed.

2. Create an Entity / EntitySet for HelperForContainsOfIntType and other such tables in EF model. Create different Entity / EntitySet for different data-types as needed.

3. Create a helper method in .NET code which takes the input of an IEnumerable and returns an Guid. This method generates a new Guid and inserts the values from IEnumerable into HelperForContainsOfIntType along with the generated Guid. Next, the method returns this newly generated Guid to the caller. For fast inserting into HelperForContainsOfIntType table, create a stored-procedure which takes input of an list of values and does the insertion. See Table-Valued Parameters in SQL Server 2008 (ADO.NET). Create different helpers for different data-types or create a generic helper method to handle different data-types.

Create a EF compiled query which is similar to something like below:

static Func<MyEntities, Guid, IEnumerable<Customer>> _selectCustomers =
    CompiledQuery.Compile(
        (MyEntities db, Guid containsHelperID) =>
            from cust in db.Customers
            join x in db.HelperForContainsOfIntType on cust.CustomerID equals x.ReferenceID where x.HelperID == containsHelperID
            select cust 
    );

Call the helper method with values to be used in the Contains clause and get the Guid to use in the query. For example:

var containsHelperID = dbHelper.InsertIntoHelperForContainsOfIntType(new int[] { 1, 2, 3 });
var result = _selectCustomers(_dbContext, containsHelperID).ToList();

I got that from Here