Add default constructor to Entity class

[evie-lau]

What's changed?

New recipe for OpenJPA -> EclipseLink migration
If class is tagged with @Entity or @MappedSuperclass, add default no-arg constructor if missing.

What's your motivation?

https://wiki.eclipse.org/EclipseLink/Examples/JPA/Migration/OpenJPA/Mappings#No-arg_Constructor

Checklist

• I've added unit tests to cover both positive and negative cases
• I've read and applied the recipe conventions and best practices
• I've used the IntelliJ IDEA auto-formatter on affected files

[timtebeek]

Great work once again! Good to see you worked out the issue with context sensitivity when injecting a constructor. Indeed that'll be down to how we generate and extract the code snippet from JavaTemplate. If you're ever curious what gets generated you can add this little snippet to the code to get the generated template.

class __P__ {
    static native <T> T p();
    static native <T> T[] arrp();
    static native boolean booleanp();
    static native byte bytep();
    static native char charp();
    static native double doublep();
    static native int intp();
    static native long longp();
    static native short shortp();
    static native float floatp();
}

class __M__ {
    static native Object any(Object o);

    static native Object any(java.util.function.Predicate<Boolean> o);

    static native <T> Object anyT();
}

public class MissingNoArgConstructorEntity {
    private int id;

    public MissingNoArgConstructorEntity(int id) {
    }

    /*__TEMPLATE__*/
    public MissingNoArgConstructorEntity() {
    }/*__TEMPLATE_STOP__*/
}

For constructors specifically we need that context sensitivity, as otherwise the generated template does not compile.

Hope that helps you on your next one!

[timtebeek]

Once again we'll wait for @cjobinabo to merge when convenient there! :)

[evie-lau]

Reverted recent change because @Entity annotation can never be used on an inner class