关于key

举个例子

hbm1

 <set name="childrenReplies" lazy="false" cascade="all" >        <key column="PARENT_REPLY_ID"/>        <one-to-many class="Reply"/>    </set>

用hbm1时,当你想l取出childrenReplies

Hibernate: select replies0_.MESSAGEBOX_ID as MESSAGEBOX5_1_1_, replies0_.id as id1_, replies0_.id as id2_0_, replies0_.title as title2_0_, replies0_.content as content2_0_, replies0_.PARENT_REPLY_ID as PARENT4_2_0_, replies0_.MESSAGEBOX_ID as MESSAGEBOX5_2_0_, replies0_.SEND_REPLY_PERSON_ID as SEND6_2_0_, replies0_.SEND_REPLY_TIME as SEND7_2_0_ from reply replies0_ where replies0_.PARENT_REPLY_ID=?
16:50:50,847 TRACE BasicBinder:82 - binding parameter [1] as [VARCHAR] - 402845ca3daa5a9a013daa5ced790000

hbm2

 <set name="childrenReplies" lazy="false" cascade="all" >        <key column="id"/>        <one-to-many class="Reply"/>    </set>

而hbm2

Hibernate: select replies0_.MESSAGEBOX_ID as MESSAGEBOX5_1_1_, replies0_.id as id1_, replies0_.id as id2_0_, replies0_.title as title2_0_, replies0_.content as content2_0_, replies0_.PARENT_REPLY_ID as PARENT4_2_0_, replies0_.MESSAGEBOX_ID as MESSAGEBOX5_2_0_, replies0_.SEND_REPLY_PERSON_ID as SEND6_2_0_, replies0_.SEND_REPLY_TIME as SEND7_2_0_ from reply replies0_ where replies0_ID=?
16:50:50,847 TRACE BasicBinder:82 - binding parameter [1] as [VARCHAR] - 402845ca3daa5a9a013daa5ced790000

忽略那些列名，主要看where从句

让我们看下文档

7.2.1. Collection foreign keys

On the database level collection instances are distinguished by the foreign key of the entity that owns the collection. This foreign key is referred to as thecollection key column, or columns, of the collection table. The collection key column is mapped by the@JoinColumn annotation respectively the<key> XML element.

key就相当于  where replies0_.PARENT_REPLY_ID=?
中的PARENT_REPLY_ID，而?就是多对一的外键指向的键

比如

 CONSTRAINT "FK_REPLY_REFERENCE_REPLY" FOREIGN KEY ("PARENT_REPLY_ID")  REFERENCES "SCOTT"."REPLY" ("ID") ENABLE, 

因为外键PARENT_REPLY_ID指向的是reply的id

所有?就是reply的id即402845ca3daa5a9a013daa5ced790000