Grails：在组合键上映射域类字段

Question

I have a domain class reverse engineered from a legacy table

class AuditLog {

    String className;
    String eventName;
    ...
    AuditEvent event; //need to add this one

    static mapping = {
        ...
        className column: 'class_name';
        eventName column: 'event_name';
        ...
    }
}

className contains the name of domain class that was changed (eg com.test.Class1) and eventName contains the name of the event performed (eg INSERT/UPDATE/DELETE).

I need to provide a human-readable description of what happened. So I created another domain class

class AuditEvent {

    String name;

    //these should make a composite key
    String className; 
    String eventName;

}

eg AuditEvent[name:"Row inserted into Class1", className:"com.test.Class1", eventName:"INSERT"].
AuditEvent[name:"Row deleted from Class1", className:"com.test.Class1", eventName:"DELETE"]

What I want now is to be able to call AuditLog.get(1).event.name and this is where I'm stuck.

How do I describe the relation for the event field in AuditLog class to make it load the right AuditEvent object depending on AuditLog.className and AuditLog.eventName?

Answer 1

Since the classname and eventname are in the AuditEvent object, you don't need them in the AuditLog class. You will, however have to create/lookup the AuditEvent when you create your AuditLog instances. ie. The two fields won't automatically be injected:

new AuditLog(event: AuditEvent.findOrSaveWhere(className: .., eventName: ..)).save()

You may be better off not making the association in the classes, but rather have a method on the AuditLog class which looks up the AuditEvent:

class AuditEvent {
    // ..
    static AuditEvent get(className, eventName) {
        find 'from AuditEvent e where e.className = :className and e.eventName = :eventName', [className: className, eventName: eventName]
    }
}

class AuditLog {

    String className;
    String eventName;

    // ...

    String getEventName() {
        AuditEvent.get(className, eventName).name
    }
}

That would make your name lookup like:

AuditLog.get(id).eventName

Answer 2

Why do you need a composite primary key for AuditEvent ?

What about hasOne ?

class AuditLog {
    static hasOne = [event: AuditEvent]
}

class AuditEvent {

    String name

    AuditLog auditLog 

}