Inheritance Mapping

Reducing Mapping XML when using base class attributes

Properties that are of the same name do not need to be specified in the mapping xml file unless hints are needed.

If you are mapping subclasses that also have have base class attributes requiring mapping XML, you might be inclined to reproduce base class field maps in each subclass mapping element, like the following example:

<mapping>
    <class-a>com.github.dozermapper.core.vo.SubClass</class-a>
    <class-b>com.github.dozermapper.core.vo.SubClassPrime</class-b>
    <field>
        <!-- this is the same for all sub classes -->
        <a>superAttribute</a>
        <b>superAttr</b>
    </field>
    <field>
        <a>attribute2</a>
        <b>attributePrime2</b>
    </field>
</mapping>
<mapping>
    <class-a>com.github.dozermapper.core.vo.SubClass2</class-a>
    <class-b>com.github.dozermapper.core.vo.SubClassPrime2</class-b>
    <field>
        <!-- this is the same for all sub classes -->
        <a>superAttribute</a>
        <b>superAttr</b>
    </field>
    <field>
        <a>attribute2</a>
        <b>attributePrime2</b>
    </field>
</mapping>

In the previous mapping, some of the fields were from a common base class, but you had to reproduce them into each mapping of the sub classes.

However, a better way to do it would be to map the base class individually. This can be done for each base class (in the case of a larger heirarchy). Assuming the base class name, below is the refactored mapping xml:

<mapping>
    <class-a>com.github.dozermapper.core.vo.SuperClass</class-a>
    <class-b>com.github.dozermapper.core.vo.SuperClassPrime</class-b>
    <field>
        <a>superAttribute</a>
        <b>superAttr</b>
    </field>
</mapping>
<mapping>
    <class-a>com.github.dozermapper.core.vo.SubClass</class-a>
    <class-b>com.github.dozermapper.core.vo.SubClassPrime</class-b>
    <field>
        <a>attribute</a>
        <b>attributePrime</b>
    </field>
</mapping>
<mapping>
    <class-a>com.github.dozermapper.core.vo.SubClass2</class-a>
    <class-b>com.github.dozermapper.core.vo.SubClassPrime2</class-b>
    <field>
        <a>attribute2</a>
        <b>attributePrime2</b>
    </field>
</mapping>

The following images explain some of the different scenarios dozer handles. Each diagram shows two mapped class hierarchies and existing relations, which Dozer recognizes and maps.

scenario1

Scenario 1 shows that if you map SubClass to ClassPrime all attributes from SuperClass → ClassPrime will be mapped as well.

scenario2

Scenario 2 shows that Dozer has no limitations on the inheritance depth it analyzes to find parent mappings.

scenario3

Scenario 3 shows that it is possible to map two collections with different subctypes of the same parent type. This is done by providing hints to the collection mapping, describing all potential subclasses.

<field>
    <a>aList</a>
    <b>bList</b>
    <a-hint>B1,B2</a-hint>
    <b-hint>BPrime1,BPrime2</b-hint>
</field>

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