NHibernate：基于非主键的many-to-one关联映射咨询

Absolutely you can make this work! Hibernate’s many-to-one mapping totally supports associating entities via non-primary key fields—you just need to use the property-ref attribute to specify which non-key field to use for the join. Let me break down the exact configuration for you.

Step 1: Configure the many-to-one in A.hbm.xml #

In your A.hbm.xml file, add the many-to-one element pointing to the B entity. The key here is using property-ref to tell Hibernate to use the Name field (instead of B's primary key) for the association:

<class name="com.yourpackage.A" table="A">
    <!-- Primary key mapping for A -->
    <id name="id" column="Id" type="java.lang.Long">
        <generator class="native"/>
    </id>
    
    <!-- A's own Name field -->
    <property name="name" column="Name" type="java.lang.String"/>
    
    <!-- Many-to-one association to B, using Name fields for matching -->
    <many-to-one 
        name="b" 
        class="com.yourpackage.B" 
        column="Name" 
        property-ref="name"/>
</class>

Step 2: Ensure B's mapping is set up correctly #

In B.hbm.xml, make sure the Name field is mapped, and it’s strongly recommended to add a unique constraint (since a many-to-one expects a single matching B instance; duplicate Names in B would cause unexpected behavior or errors):

<class name="com.yourpackage.B" table="B">
    <!-- Primary key mapping for B -->
    <id name="id" column="Id" type="java.lang.Long">
        <generator class="native"/>
    </id>
    
    <!-- B's Name field, marked as unique -->
    <property 
        name="name" 
        column="Name" 
        type="java.lang.String" 
        unique="true"/>
</class>

Key Details to Note #

• column="Name" in the many-to-one element refers to the column in table A that holds the value to match against table B's Name column.
• property-ref="name" is the critical part: it tells Hibernate to use the name property of the B entity (and its corresponding database column) instead of B's primary key for the association.
• Unique Constraint: Always ensure table B's Name column is unique. If multiple B records have the same Name, Hibernate won't know which one to associate with an A record, leading to exceptions or incorrect results.

内容的提问来源于stack exchange，提问作者Powerslave