Mybatis config

In mybatis config file, there are three elements about lazy fetch:

<settings> 
  <setting name="lazyLoadingEnabled" value="true"/> 
  <setting name="aggressiveLazyLoading" value="false"/>
  <setting name="lazyLoadTriggerMethods"
    value="equals,clone,hashCode,toString"/>
</settings>

1. lazyLoadingEnabled. Globally enables or disables lazy loading. Default value is false.

   This value can be override by fetchType, its valid values are lazy and eager e.g. <association ... fetchType="lazy" />

2. aggressiveLazyLoading. When enabled, any method call will load all the lazy properties of the object. Otherwise, each property is loaded on demand.

   This value should be set false.

   Default value is false. However its default is true in <=3.4.1

3. lazyLoadTriggerMethods. Specifies which Object’s methods trigger a lazy load. Default value is : equals,clone,hashCode,toString.

   That means equals(),clone(),hashCode(),toString() of any filed will trigger lazy load.

4. Both backend and frontend can trigger lazy load when corresponding field is accessed.

   For example, there is object Teacher, its field address is defined as lazy load, then when teacher.getAddress() or teacher.address(such as in struts program, define ${teacher.address} in jsp page) is called, the lazy load will run.

5. Because default value of lazyLoadTriggerMethods is equals,clone,hashCode,toString, you cannot make sure all of the code will not call these methods, especially for 3rd framework/utility/implementation.

   For instance, there is object Teacher, its field address is defined as lazy load. In a struts program, if developer use ${teacher.id} in jsp page, then it will trigger lazy load even there is no call about address.

   Thus, lazyLoadTriggerMethods should be set empty like <setting name="lazyLoadTriggerMethods" value=""/>

Conclusion

In order to implement lazy load in mybatis, configuration should be:

  <settings>
		<setting name="aggressiveLazyLoading" value="false" /><!-- this has to be set as false if mybatis ≤3.4.1 -->
		<setting name="lazyLoadTriggerMethods" value=""/>
	</settings>

and fetchType="lazy" or lazyLoadingEnabled is true.