var fooIds = new List<int> { 2, 3, 4}
var foosToChange = Foo.Where(f => fooIds.Contains(f.Id));
// Update foosToChange and save here

var fooIds = new []
  {
    new { prop1 = "12345", prop2 = 2017111701 },
    new { prop1 = "hij", prop2 = 2018060101 },
  };

var foosToChange = Foo.Where(f => fooIds.Contains(???));