Support contains (#527)

moor/lib/src/runtime/query_builder/expressions/text.dart

@@ -17,6 +17,13 @@ extension StringExpressionOperators on Expression<String> {
     return _LikeOperator(this, Variable.withString(regex), operator: 'REGEXP');
   }
 
+  /// Whether this expression contains [substring].
+  ///
+  /// This is equivalent to calling [like] with `%<substring>%`.
+  Expression<bool> contains(String substring) {
+    return like('%$substring%');
+  }
+
   /// Uses the given [collate] sequence when comparing this column to other
   /// values.
   Expression<String> collate(Collate collate) {

moor/test/expressions/expressions_integration_test.dart

@@ -32,4 +32,14 @@ void main() {
     expect(row.read(tomorrowStamp) - row.read(nowStamp),
         const Duration(days: 1).inSeconds);
   });
+
+  test('text contains', () async {
+    const stringLiteral = Constant('Some sql string literal');
+    final containsSql = stringLiteral.contains('sql');
+
+    final row =
+        await (db.selectOnly(db.users)..addColumns([containsSql])).getSingle();
+
+    expect(row.read(containsSql), isTrue);
+  });
 }

moor/test/expressions/text_test.dart

@@ -31,6 +31,11 @@ void main() {
     expect(ctx.boundVariables, isEmpty);
   });
 
+  test('can use contains', () {
+    expect(
+        expression.contains('foo bar'), generates('col LIKE ?', ['%foo bar%']));
+  });
+
   test('can use string functions', () {
     expect(expression.upper(), generates('UPPER(col)'));
     expect(expression.lower(), generates('LOWER(col)'));