The descriptor can also provide the same metadata information about the entities as annotations, such as primary key field, and any mappings between objects.
描述符也可以提供与注释相同的有关实体的元数据信息，如主键字段，以及对象之间的任何映射。
2
You cannot have two fieldmappings to the same type of artifact.
您不能拥有同一类型工件的两个区域映射。
3
You cannot assign the fieldmappings until these mandatory fields are populated.