Dart APIunself_local_databaseFieldCompanionunique unique property Null safety Value<bool> unique final Implementation final Value<bool> unique; unself_local_database unself_local_database FieldCompanion unique property FieldCompanion class Constructors FieldCompanion insert Properties collectionId created extra hashCode id name required runtimeType system type unique updated Methods copyWith noSuchMethod toColumns toString Operators operator == Static methods custom