IQueryable.Where() suitable Expression in where?

Question

I\'m very low experienced with Expressions in .NET, that\'s why I rather ask you guys. How should I - see comment below:

using P = Myclass;
..
S         


        

Answer 1

You can't "OR" lambdas together that way. You really want to "OR" the lambda bodies together. Here's a method to do that:

public static Expression> OrTheseFiltersTogether( 
  this IEnumerable>> filters) 
{ 
    Expression> firstFilter = filters.FirstOrDefault(); 
    if (firstFilter == null) 
    { 
        Expression> alwaysTrue = x => true; 
        return alwaysTrue; 
    } 

    var body = firstFilter.Body; 
    var param = firstFilter.Parameters.ToArray(); 
    foreach (var nextFilter in filters.Skip(1)) 
    { 
        var nextBody = Expression.Invoke(nextFilter, param); 
        body = Expression.OrElse(body, nextBody); 
    } 
    Expression> result = Expression.Lambda>(body, param); 
    return result; 
} 

Then later:

Expression> myFilter1 = x => foo1 == true && foo2 == false;  
Expression> myFilter2 = x => ... ;  
..  
List>> filters = new List>>();
filters.Add(myfilter1);
filters.Add(myfilter2);
..  
Expression> resultFilter = filters.OrTheseFiltersTogether();
IQueryable
 query = query.Where(resultFilter);