public static Expression Parameterize(Type type, object value)
{
// () => new LinqParameterContainer(constant).Property
// instead of returning a constant expression node, wrap that constant in a class the way compiler
// does a closure, so that EF can parameterize the constant (resulting in better performance due to expression translation caching).
LinqParameterContainer containedValue = LinqParameterContainer.Create(type, value);
return(Expression.Property(Expression.Constant(containedValue), "TypedProperty"));
}
// Extract the constant that would have been encapsulated into LinqParameterContainer if this
// expression represents it else return null.
internal static object ExtractParameterizedConstant(Expression expression)
{
if (expression.NodeType == ExpressionType.MemberAccess)
{
MemberExpression memberAccess = expression as MemberExpression;
Contract.Assert(memberAccess != null);
if (memberAccess.Expression.NodeType == ExpressionType.Constant)
{
ConstantExpression constant = memberAccess.Expression as ConstantExpression;
Contract.Assert(constant != null);
Contract.Assert(constant.Value != null);
LinqParameterContainer value = constant.Value as LinqParameterContainer;
Contract.Assert(value != null, "Constants are already embedded into LinqParameterContainer");
return(value.Property);
}
}
return(null);
}