Dynamic IN (list.Contains in a query)

Summary#

Inside a query predicate, list.Contains(e.Column) tests each row's column for membership in a runtime List<T> — exactly the C#/LINQ spelling for SQL IN. It lowers to e.Column = ANY(@p), binding the whole list as one array parameter (stable SQL shape). The list is a local you build at run time; an empty list matches nothing.

Signature#

Entity.Where(e => <list>.Contains(e.<Column>))    // → e.Column = ANY(@p)

Description#

The receiver <list> is any local collection (a new List<T>() you populate, a Text.Split result, …) whose element type is comparable to the column — same rule as a literal IN or ==: exact for string/bool/DateTime, id-coercion between Guid and string, and numeric widening (int→long→decimal→double). An incompatible pair is a compile error.

This is position-sensitive: the same list.Contains(x) written outside a query predicate is the ordinary in-memory list-membership check. It becomes a SQL IN only inside a Where/Any/Count/… predicate, where x is a row column.

A literal list works too and is equivalent: [a, b, c].Contains(e.Column) (rendered as IN (…)); the runtime-list form is the one that lets the set be computed at run time.

Examples#

entity Ticket { string Status; }

List<Ticket> ByIds(List<Guid> ids) {
  return Ticket.Where(t => ids.Contains(t.Id)).ToList();   // t.Id = ANY(@p)
}

List<Ticket> ByStatuses() {
  var open = new List<string>();
  open.Add("New");
  open.Add("InProgress");
  return Ticket.Where(t => open.Contains(t.Status)).ToList();   // empty `open` → no rows
}

See also#

• Union / Concat / Intersect / Except — combining whole row-sets (Union/Intersect/Except)
• List OrderBy (in-memory) — ranking a local list in memory