NotSupportedException using ToList () in LINQ and EntityFramework

Question

I have a query that looks like this:

var q = from x in db.Table1 where x.Timestamp.CompareTo(fromDate) >= 0 && x.Timestamp.CompareTo(toDate) < 0 select x; var q_list = q.ToList(); // this works fine var g = q.Where(z=> z.Table2.Equals(ns)); // ns is instance of Table2 not Table1 var g_list = g.ToList(); // this throws exception 

An exception:

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 System.NotSupportedException was unhandled Message=Unable to create a constant value of type ... 

I have many such functions, and I do not want to repeat requests, I need to use the Where, GroupBy ... functions and others.

FULL exception tracing:

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 System.NotSupportedException was unhandled Message=Unable to create a constant value of type 'DataAccessLayer.Model.Table2. Only primitive types ('such as Int32, String, and Guid') are supported in this context. Source=System.Data.Entity StackTrace: at System.Data.Objects.ELinq.ExpressionConverter.ConstantTranslator.TypedTranslate(ExpressionConverter parent, ConstantExpression linq) at System.Data.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq) at System.Data.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) at System.Data.Objects.ELinq.ExpressionConverter.EqualsTranslator.TypedTranslate(ExpressionConverter parent, BinaryExpression linq) at System.Data.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq) at System.Data.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) at System.Data.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input) at System.Data.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input, DbExpressionBinding& binding) at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, DbExpression& source, DbExpressionBinding& sourceBinding, DbExpression& lambda) at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call) at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.SequenceMethodTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, SequenceMethod sequenceMethod) at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq) at System.Data.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq) at System.Data.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) at System.Data.Objects.ELinq.ExpressionConverter.Convert() at System.Data.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable`1 forMergeOption) at System.Data.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption) at System.Data.Objects.ObjectQuery`1.System.Collections.Generic.IEnumerable<T>.GetEnumerator() at System.Data.Entity.Internal.Linq.InternalQuery`1.GetEnumerator() at System.Data.Entity.Infrastructure.DbQuery`1.System.Collections.Generic.IEnumerable<TResult>.GetEnumerator() at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection) 

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Answer 1

The problem is that EntityFramework does not understand types that are not primitive. What you need to do is:

 var g = q.Where(z => z.field.Id.Equals(ns.Id)); 

Keep in mind that if you have a regular implementation of Equals , then it cannot be translated to the correct t-sql. If you still want to implement this implementation, you need to do this in memory:

 // note it using q_list instead of q var g = q_list.Where(z => z.field.Equals(ns));