Is there any way to get Linq-to-entities to evaluate a local expression

Lets say you have the following linq expression:

from o in salesEntities.Orders where o.OrderDate < DateTime.Today.AddDays(-20) select o

Entity Framework does not know how to translate DateTime.Today.AddDays(-20) into an Entity SQL expression, and you get the following error:

LINQ to Entities does not recognize the method 'System.DateTime AddDays(Double)' method, and this method cannot be translated into a s开发者_如何学编程tore expression.

So here is my questions: Is there any way to get Linq to Entities to evaluate part of the lambda expression and substitute a constant value, without me having to declare a local variable to hold it?

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LINQ-to-Entities can deal with local values but not local expressions. Your code will work with this minor change:

var pastDate = DateTime.Today.AddDays(-20);

from o in salesEntities.Orders where o.OrderDate < pastDate select o

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Change your expression using the EntityFunction for add days like this:

var result =
(
from o in salesEntities.Orders 
where o.OrderDate < System.Data.Objects.EntityFunctions.AddDays(DateTime.Today,-20) 
select o
);

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The short answer is no. Everything in a linq to entities expression must be either in a local variable or able to be translated into a sql expression by the entity framework.