I'm trying to build an Expression Tree that reflects a "select new" query.
I'm using Ethan's answer to this question . It works great for common lists but with LINQ to Entities I get this exception:
System.NotSupportedException: Unable to create a constant value of type X.
Only primitive types or enumeration types are supported in this context.
Where X is the Entity I'm querying.
Using the debugger this is the IQueryable with the expression tree:
SELECT [Extent1].[Id] AS [Id],
[Extent1].[Nombre] AS [Nombre],
[Extent1].[Apellido] AS [Apellido]
FROM [dbo].[Empleadoes] AS [Extent1]
.Select(t => new Nombre;String;() {Nombre = t.Nombre})
And this is the IQueryable using normal linq notation (not actually the same query but to get the point - they are different)
SELECT [Extent1].[Dni] AS [Dni],
[Extent1].[Nombre] + N' ' + [Extent1].[Apellido] AS [C1]
FROM [dbo].[Empleadoes] AS [Extent1]
Any help appreciated. Thanks.
Looking through Dynamic LINQ code I found the problem.
Ethan's solution does this:
source.Provider.CreateQuery(
Expression.Call(
typeof(Queryable),
"Select",
new Type[] { source.ElementType, dynamicType },
Expression.Constant(source),
selector));
And inside Dynamic.cs of Dynamic LINQ they do this:
source.Provider.CreateQuery(
Expression.Call(
typeof(Queryable),
"Select",
new Type[] { source.ElementType, lambda.Body.Type },
source.Expression,
Expression.Quote(lambda)));
The relevant change is in the 4th parameter of the call to Expression.Call.
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