不需要no-arg构造函数的JPA实现

Question

Is there an ORM framework which implements JPA but doesn't require default (no-arg) constructor from @Entity classes?

AFAIK, it is said in JPA documentation that an @Entity should have default constructor, but can an implementation support constructor arguments injection (or maybe unsafe object instantiation) and therefore work with classes without a default constructor?

This feature would help a lot to ensure immutability (which standard JPA lacks) and would let the developer keep strict invariants on class instance state (eg its fields always have the correct value).

By the way, when using Kotlin, the need of no-arg constructor interferes with good code style and coding conventions.

There's JIRM library which deals with constructor injection and immutability, but it's not a complete JPA implementation.

So, does any of the JPA ORMs support @Entity classes with no default constructor?

Answer 1

Is there an ORM framework which implements JPA but doesn't require default (non-arg) constructor from @Entity classes?

No, because it would break the specification. The below quote is from page 23 of the JPA 2.1 specification :

The entity class must have a no-arg constructor. The entity class may have other constructors as well. The no-arg constructor must be public or protected.

Having said that, there might exist some ORM framework that implements JPA partially that ignores this feature.

Answer 2

是的，我尝试使用EclipseLink 2.5.2，即使没有提供，也可以正常工作。