Question

I’m currently have Lambda Expresion: http://pastebin.com/ZGCiQdHe

And i get ArgumentException in 53 line
http://msdn.microsoft.com/en-us/library/bb340145(v=vs.90).aspx

var lExpresion = Expression.Lambda<Func<TEntity, bool>>(body, parametrsNumber, parametrsTyp, parametrsLp);

But i not understand what i do wrong.

I want to get:

    WHERE ((twr_gidnumer =1 and twr_gidtyp = 1 and twr_gidlp = 1) OR 
    (twr_gidnumer =1 and twr_gidtyp = 1 and twr_gidlp = 2))

–ANSWERR FULL

Based on article:

http://blogs.msdn.com/b/mattwar/archive/2007/07/31/linq-building-an-iqueryable-provider-part-ii.aspx
https://stackoverflow.com/Converting 2 argument Lambda expression to 1 argument Lambda expression

public static Expression<Func<CDNXL_TwrKarty, bool>> Bind2nd(Expression<Func<CDNXL_TwrKarty, CDNXL_TwrKarty,CDNXL_TwrKarty, bool>> source)
{
    Expression newBody = new Rewriter(source.Parameters[0]).Visit(source.Body);
    return Expression.Lambda<Func<CDNXL_TwrKarty, bool>>(newBody, source.Parameters[0]);
}

internal class Rewriter : ExpressionVisitor
{
    private readonly ParameterExpression candidate_;

    public Rewriter(ParameterExpression candidate)
    {
        candidate_ = candidate;
    }

    protected override Expression VisitParameter(ParameterExpression p)
    {
        return candidate_;
    }
}

//REPLACE EXECUTING PLACE
var retMultiLamnda = Expression.Lambda<Func<CDNXL_TwrKarty, CDNXL_TwrKarty, CDNXL_TwrKarty, bool>>(body, parametrsNumber, parametrsTyp, parametrsLp);
var retOneLambda = Bind2nd(retMultiLamnda);
var retQuery = query.Where(retOneLambda);
return retQuery;

Thanx Rafal for Help.

Answer 1

First thing that I see is that your delegate type does not math with your invocation list. You expect to create function that receives one argument of type TEntity and yet you pass tree parameter expressions to function. Note that you execute this overload of Lablda method.

OK, I’ll try to be more clear:

Expression.Lambda<Func<Arg1Type,...,ArgNType,ReturnType>>
    (body,parameterExpressionForArg1,...,parameterExpressionForArgN);

Those generic arguments ArgType must match with parameterExpressionsForArg. There must be equal number of generic types for argumetnts as parameterExpressions for arguments. And types of those must also match.

So if you want to have tree parameterExpressions for some reason then you have to have tree arguments in your method:

 Expression.Lambda<Func<CDNXL_TwrKarty,CDNXL_TwrKarty,CDNXL_TwrKarty, bool>>(body, parametrsNumber, parametrsTyp, parametrsLp); 

might be correct call in this case obviously it wont match the Where call.

If you want to merge tree expressions into one matching Where argument then you have to replace all redundant ParamteterExpressions.