Why my LINQ expression do not work in LINQ to SQL?

Question

private System.Linq.Expressions.Expression<Func<ActionLogs, bool>> GetExpression()
{
    Expression<Func<ActionLogs, bool>> expr = w => w.ID != -1;
    if (ActionDate != null)
    {
        Expression<Func<ActionLogs, bool>> byDate = w => w.DateAction == ActionDate;
        var body = Expression.AndAlso(expr.Body, byDate.Body);
        expr = Expression.Lambda<Func<ActionLogs, bool>>(body, expr.Parameters[0]);
    }

    if (ActionType != ActionTypeEnum.Empty)
    {
        Expression<Func<ActionLogs, bool>> byActionType = w => w.ActionTypeID == (int)ActionType;
        var body = Expression.AndAlso(expr.Body, byActionType.Body);
        expr = Expression.Lambda<Func<ActionLogs, bool>>(body, expr.Parameters[0]);
    }

    if (!String.IsNullOrWhiteSpace(AuthorLogin))
    {
        Expression<Func<ActionLogs, bool>> byLogin = w => w.User.LoginName == AuthorLogin;
        var body = Expression.AndAlso(expr.Body, byLogin.Body);
        expr = Expression.Lambda<Func<ActionLogs, bool>>(body, expr.Parameters[0]);            
    }

    if (!String.IsNullOrWhiteSpace(AdditionalInfo))
    {
        Expression<Func<ActionLogs, bool>> byAdditionalInfo = w => w.DescriptionText.Contains(AdditionalInfo);
        var body = Expression.AndAlso(expr.Body, byAdditionalInfo.Body);
        expr = Expression.Lambda<Func<ActionLogs, bool>>(body, expr.Parameters[0]);
    }

    return expr;
}

This is the function that generate my expression.

and when i do this:

 System.Linq.Expressions.Expression<Func<ActionLogs, bool>> expr = GetExpression(); 
 result = blablabla.Where(expr);

It says to me that The parameter 'w' is not in scope.

So the question is, how i can generate my expression, that depends on something i need, and paste it into LINQ to SQL query?

Answer 1

Could it be that you are trying to return an Expression.Lambda<T> and then assign it to an object that is a SON of it on its hierarchy(System.Linq.Expressions.Expression<T>)

Please take a look at http://msdn.microsoft.com/en-us/library/system.linq.expressions.lambdaexpression.aspx

Hope that helps,

Answer 2

public Expression<Func<T, bool>> Combine<T>(Expression<Func<T, Boolean>> first, Expression<Func<T, Boolean>> second)
{
    var toInvoke = Expression.Invoke(second, first.Parameters.Cast<Expression>());
    return (Expression.Lambda<Func<T, Boolean>>(Expression.AndAlso(first.Body, toInvoke), first.Parameters));
}

This function was very helpful. It combined two expressions and built correct tree.