The MapKeyConvert annotation specifies that a named converter should be used with the corresponding mapped attribute key column. The MapKeyConvert annotation has the following reserved names: - serialized: Will use a SerializedObjectConverter on the associated mapping. When using a SerializedObjectConverter the database representation is a binary field holding a serialized version of the object and the object-model representation is a the actual object - class-instance: Will use an ClassInstanceConverter on the associated mapping. When using a ClassInstanceConverter the database representation is a String representing the Class name and the object-model representation is an instance of that class built with a no-args constructor - none - Will place no converter on the associated mapping. This can be used to override a situation where either another converter is defaulted or another converter is set. When these reserved converters are not used, it is necessary to define a converter to use using the @Converter annotation.