Question

Is it possible to create a custom lambda function that I can replace with the .Contains()/.StartsWith()/EndsWith() calls below?

If so, I don’t have to compare the search string here, but I can do it in this custom function. This would remove 2/3 of the code below, if I’m right.

…or if you have any other ideas on how to minimize this I’d be glad to hear it!

private void searcher(ref Expression<Func<Party, bool>> predicate, string search, string keyword, string column)
{
    if (search == "contain")
    {
        if (column == "surname") predicate = predicate.And(p => p.surname.Contains(keyword));
        if (column == "lastname") predicate = predicate.And(p => p.lastname.Contains(keyword));
        if (column == "comment") predicate = predicate.And(p => p.comment.Contains(keyword));
        if (column == "position") predicate = predicate.And(p => p.position.Contains(keyword));
    }
    else if (search == "start")
    {
        if (column == "surname") predicate = predicate.And(p => p.surname.StartsWith(keyword));
        if (column == "lastname") predicate = predicate.And(p => p.lastname.StartsWith(keyword));
        if (column == "comment") predicate = predicate.And(p => p.comment.StartsWith(keyword));
        if (column == "position") predicate = predicate.And(p => p.position.StartsWith(keyword));
    }
    else if (search == "end")
    {
        if (column == "surname") predicate = predicate.And(p => p.surname.EndsWith(keyword));
        if (column == "lastname") predicate = predicate.And(p => p.lastname.EndsWith(keyword));
        if (column == "comment") predicate = predicate.And(p => p.comment.EndsWith(keyword));
        if (column == "position") predicate = predicate.And(p => p.position.EndsWith(keyword));
    }
}

Answer 1

Might be tempted to write an extension for string (Note this would be better still with an enum for where):

public static bool Exists(this string str, string where, string what)
{
   if(where == "start") return str.StartsWith(what);
   if(where == "end") return str.EndsWith(what);
   if(where == "contain") return str.Contains(what);
   return false;
}

Then your code becomes a bit simpler:

private void searcher(ref Expression<Func<Party, bool>> predicate, string search, string keyword, string column)
{
    if (column == "surname") predicate = predicate.And(p => p.surname.Exists(search ,keyword));
    if (column == "lastname") predicate = predicate.And(p => p.lastname.Exists(search ,keyword));
    if (column == "comment") predicate = predicate.And(p => p.comment.Exists(search ,keyword));
    if (column == "position") predicate = predicate.And(p => p.position.Exists(search ,keyword));
}