Hibernate session.load不会填充对象的arraylist属性

Question

I've got a problem using hibernate's session.load function. I try to get an object according to an ID, and it returns a good object, but only primitive properties are set in the instance. I have a property with is a set (mapped to some other object), but it's not retrieved after set, and the set's field is null.

Does anyone have a clue why the fetching doesn't work as expected ?

Thanks

Answer 1

Check your fetching strategy on the ORM. Some of the properties could be set to lazy instead of eager. You might have to use Hibernate.Initialize after the load to fill all properties. Otherwise, you'll have to modify your ORM to use eager loading. Using annotaions, you would set the following property after the @entity attribute to turn off lazy by default:

@org.hibernate.annotations.Proxy(lazy = false)

However, this will cause everything to load upon fetch.

Answer 2

I guess the Set is lazy loaded, if you want it to be populated you can simply call the getter of that Set and it will be loaded. If you want it to be loaded all the time you can add

fetch = FetchType.EAGER

example:

@OneToMany(mappedBy = "program", fetch=FetchType.EAGER)
private final List<Instruction> instructions = new ArrayList<Instruction>();

to the mapping of your entity

Answer 3

Unless you are 100% positive you will always want the children to be loaded, setting EAGER fetching could lead to undesired effects. The JBoss Tools set fetching to LAZY by default.

Instead, you need to initialize the child association, which can be done in various ways:

1. Hibernate.initialize(myObject.getChildren())
2. Call the size on the association: myObject.getChildren().size()
3. In a Criteria query, set the FetchMode on the association to JOIN : criteria.setFetchMode("children", FetchMode.JOIN);