Unable to construct a constant variable of type †System.Objectâ€TM in Entity Framework - Linq. There are only primitive kinds.

entity-framework expression-trees linq

Question

I have a method to build an expression for a linq query for a given type, property, and value. This works wonderfully as long as the property on the type is NOT nullable. Here is the example I am working from (http://www.marcuswhitworth.com/2009/12/dynamic-linq-with-expression-trees) I am calling the Equals method on the property. However I have discovered that the Equals method for Nullable types takes an Object as a parameter instead of the Nullable type. I attempted to use GetValueOrDefault to hide the null values but EF doesn't support that method. As a simple example the following code will throw an error:

decimal? testVal = new decimal?(2100);
        var test = (from i in context.Leases where i.AnnualRental.Equals(testVal) select i).ToList();

However if you use == instead of the Equals() method it will work OK. I am not sure how to convert the code to use == instead of Equals() however. Any suggestions will be greatly appreciated.

1
1
12/8/2010 5:46:25 PM

Popular Answer

If you say ==, you generate a BinaryExpression with NodeType as ExpressionType.Equal. http://msdn.microsoft.com/en-us/library/bb361179.aspx

If you say .Equals(x), you generate a MethodCallExpression. The MethodCallExpressions that LinqToEntities may translate into Sql is a limitted list (for example none of your own undecorated methods are in that list). Nullable<T>.Equals(x) is apparently not on that list.

Don't say .Equals(x) to LinqToEntities.

3
12/8/2010 6:31:31 PM


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