Use string as field name in LINQ

c#, linq, linq-to-objects, linq-to-sql

Solution

You need to forget about the anonymous type, maybe use `Tuple<int,string>` instead; but: how about:

IQueryable<Foo> source = // YOUR SOURCE HERE
      // in-memory dummy example:
      // source = new[] {
      //    new Foo {Id = 1, Bar = "abc"},
      //    new Foo {Id = 2, Bar = "def"}
      // }.AsQueryable();

string field = "Bar";
string stringToSearch = "d";
var param = Expression.Parameter(typeof (Foo), "x");
var predicate = Expression.Lambda<Func<Foo, bool>>(
    Expression.Call(
        Expression.PropertyOrField(param, field),
        "Contains", null, Expression.Constant(stringToSearch)
    ), param);
var projection = Expression.Lambda<Func<Foo, Tuple<int, string>>>(
    Expression.Call(typeof(Tuple), "Create", new[] {typeof(int), typeof(string)},
        Expression.PropertyOrField(param, "Id"),
        Expression.PropertyOrField(param, field)), param);
Tuple<int,string>[] data = source.Where(predicate).Select(projection).ToArray();

Problem

Look the code below. I'd like to replace `USERNAME` by the field name received in the parameter `field`. This method must be able to make some search on several fields. Thank, ``` public void Searching(string field, string stringToSearch) { var res = from user in _dataContext.USERs where user.USERNAME.Contains(stringToSearch) select new { Id = user.ID, Username = user.USERNAME }; } ```

Original source