如何在多对多关系中使用Hibernate在连接表中插入常量值？

Question

I have a mapping like A - AB - B but the AB table is also a join table for other tables (yeah, thanks, no comment :p). In the AB table, I have a CODE (non-null) column.

I can fetch the correct datas by adding a where tag in the mapping, but when I insert values, Hibernate does not add the value in the CODE column... Well, I don't know how to tell Hibernate to do that.

Here is the mapping of the A table to get a Set:

      <set name="b" table="AB" lazy="false" where="CODE='1.2.3'">
        <key column="A_ID" />
          <many-to-many column="B_ID" class="B">
          </many-to-many>
      </set>

Hibernate create an insert with only the A_ID and the B_ID values, I'd like to tell Hibernate to insert CODE='1.2.3' in its SQL INSERT query.

Many thanks for your help,

UPDATE

The idea in a Java point of view is to have a signature like this in A: getB():Set<B> I do not want getAB():Set<AB> .

Thanks

Answer 1

for AB use two classes one for ID s ABIdClass(A_ID,B_ID) and the other for Code (and all extra columns) ABClass(CODE) and use default attribute of column for constant value:

<class name="ABClass" table="AB">
    <composite-id name="id" class="ABIdClass">
        <key-many-to-one name="a" class="A" column="a_id" />
        <key-many-to-one name="b" class="B" column="b_id" />
    </composite-id>
    <property name="code" type="string">
        <column name="code" not-null="false" default="1.2.3" />
    <property/>
</class>

you can also try something like this:

ABIdClass abId = new ABIdClass();
abId.setA(a);
abId.setB(b);
ABClass ab = new ABClass();
ab.setId(abId);
ab.setCode("1.2.3"); 
a.getABClass().add(ab);

---

hope these be useful.

Answer 2

You should be able to achieve what you are looking for using the Hibernate Table per Class Hierarchy approach.

abstract class Mapping { private String code; }
class TableA {}
class TableB {}
class TableAB extends Mapping { private TableA a; private TableB b; }
class TableC {}
class TableD {}
class TableCD extends Mapping { private TableC c; private TableD d; }
class TableE {}
class TableF {}
class TableEF extends Mapping { private TableE e; private TableF f; }

<class name="TableA" table="tableA"/>
<class name="TableB" table="tableB"/>
<class name="TableC" table="tableC"/>
<class name="TableD" table="tableD"/>
<class name="TableE" table="tableE"/>
<class name="TableF" table="tableF"/>
<class name="Mapping" table="mapping">
  <discriminator column="CODE" type="string"/>
  <subclass name="TableAB" discriminator-value="1.2.3">
    <property name="a" column="a_id"/>
    <property name="b" column="b_id"/>
  </subclass>
  <subclass name="TableCD" discriminator-value="4.5.6">
    <property name="c" column="a_id"/>
    <property name="d" column="b_id"/>
  </subclass>
  <subclass name="TableEF" discriminator-value="7.8.9">
    <property name="e" column="a_id"/>
    <property name="f" column="b_id"/>
  </subclass>
</class>

Note that the columns a_id and b_id are common for all relationships. This will ensure that a single mapping table can be used for different relationships as you want.