IQueryable extension method for linq2entities

Question

I am trying to implement an extension method that will work with linq2entities. I had initially assumed that if my extension method took and returned an IQueryable, and as

Answer 1

This should work without extending your query provider. It basically breaks it down to exactly what your IsCurrent func is doing.

public static class IQueryableExtensions
{
    public static IQueryable IsCurrent(this IQueryable query,
        Expression> expressionEnd,
        Expression> expressionStart,
        DateTime asOf) where T : class
    {
        // Lambdas being sent in
        ParameterExpression paramEnd = expressionEnd.Parameters.Single();
        ParameterExpression paramStart = expressionStart.Parameters.Single();

        // GT Comparison
        BinaryExpression expressionGT = ExpressionGT(expressionEnd.Body, asOf);

        // LT Comparison
        BinaryExpression expressionLT = ExpressionLE(expressionStart.Body, asOf);

        query = query.Where(Expression.Lambda>(expressionGT, paramEnd))
                     .Where(Expression.Lambda>(expressionLT, paramStart));

        return query;
    }

    private static BinaryExpression ExpressionLE(Expression body, DateTime value)
    {
        return Expression.LessThanOrEqual(body, Expression.Constant(value, typeof(DateTime)));
    }

    private static BinaryExpression ExpressionGT(Expression body, DateTime value)
    {
        return Expression.GreaterThan(body, Expression.Constant(value, typeof(DateTime)));
    }
}

And to use it

var query = db.PersonHistories.IsCurrent( p => p.Ends, 
                                          p => p.Starts, 
                                          DateTime.Now );