Allow <idref/> to set property value to id of bean [SPR-2500]

[spring-projects-issues]

George Licquorice opened SPR-2500 and commented

It is often useful to set a property of a bean to the ID of the bean. For example, the bean might have an ID property and when it is used with Spring, it would make sense for this to be set to the bean ID.

This can currently be done by using <idref> in the following way;

<bean id="myclass" class="org.myorg.MyClass" abstract="true">
... (set common properties)
</bean>
<bean id="myclass1" parent="myclass"/>
<property name="id"><idref local="myclass1"/></property>
...
</bean>
<bean id="myclass2" parent="myclass"/>
<property name="id"><idref local="myclass2"/></property>
...
</bean>

This is quite ugly however since each bean definition requires the id to be explicitly set.

I could make my bean class implement BeanNameAware and set the id based on this. While this avoids having to set the property in the config, it ties my bean class to Spring.

An alternative option would be to make <idref/> work without any attributes. In this situation it would refer to the id of the current bean. If this bean is the parent of another bean, it could resolve to the id of whatever the outermost bean is.

The definitions above would become something like this;

<bean id="myclass" class="org.myorg.MyClass" abstract="true">
<property name="id"><idref/></property>
...
</bean>
<bean id="myclass1" parent="myclass"/>
...
</bean>
<bean id="myclass2" parent="myclass"/>
...
</bean>
This is much cleaner and the bean class doesn't need any knowledge of Spring.

---

Affects: 2.0 RC2

Issue Links:

• Evaluate 'idref' element and 'local' attribute in Spring 3.1 [SPR-8179] #12830 Evaluate 'idref' element and 'local' attribute in Spring 3.1

[spring-projects-issues]

Antranig Basman commented

See also #7133

[spring-projects-issues]

Andreas Senft commented

This sounds like a useful proposal. I just wonder if it would make sense to disallow using this construct inside nested beans.
Resolving the outermost bean might not be intuitive, especially since it is not forbidden to specify an id on a nested bean.

Regards,
Andreas

[spring-projects-issues]

George Licquorice commented

If it didn't resolve to the id of the outermost bean then the syntax for the above beans would need to change as follows (if I'm understanding what you're saying);

<bean id="myclass" class="org.myorg.MyClass" abstract="true">
<property name="id"><idref/></property>
...
</bean>
<bean id="myclass1" parent="myclass"/>
<property name="id"><idref/></property>
...
</bean>
<bean id="myclass2" parent="myclass"/>
<property name="id"><idref/></property>
...
</bean>

The downside of this is that the id property of the target class needs to still be explicitly specified in each child bean.

With the original syntax, it would be legal to specify the id property explicitly to override the value of the parent bean if that is what is desired (in the same way as other properties can be overridden).

Perhaps, to avoid confusion (and to remain consistent with the existing use of idref), <idref/> should only be used to refer to the id of the bean in which it is defined (rather than the outermost bean). If the desired functionality is to resolve to the id of the outermost bean then perhaps an attribute could be specified (or even use a different element altogether).

In this way, the above would be re-written as something like;

<bean id="myclass" class="org.myorg.MyClass" abstract="true">
<property name="id"><idref outerid="true"/></property>
...
</bean>
<bean id="myclass1" parent="myclass"/>...</bean>
<bean id="myclass2" parent="myclass"/>...</bean>

or

<bean id="myclass" class="org.myorg.MyClass" abstract="true">
<property name="id"><outeridref/></property>
...
</bean>
<bean id="myclass1" parent="myclass"/>...</bean>
<bean id="myclass2" parent="myclass"/>...</bean>

[spring-projects-issues]

Andreas Senft commented

Hi George,

actually with "nested beans" I referred to anonymous nested beans and not to parent/child relationships. I think there is nothing wrong with the example in your first post.

I just wanted to point out cases like this:

<bean id="foo" class="mypkg.FooImpl">
<property name="bar">
<bean class="mypkg.BarImpl">
<property name="id"></idref></property>
</bean>
</property>
</bean>

What would you expect the id to be set to? And the nesting could go deeper than one level.

[spring-projects-issues]

George Licquorice commented

Hi Andreas,

Sorry, my misunderstanding.

Totally agree with you. I think it should be disallowed for anonymous beans.

In the example you give I would expect it to be associated with the nested class (class="mypkg.BarImpl") which wouldn't make sense given that the bean doesn't have an id.

Cheers

George

[spring-projects-issues]

Chris Beams commented

All use of xsd:ID and xsd:IDREF has been removed from the spring-beans schema for 3.1 in order to accommodate nested <beans> elements, bean definition profiles, etc.