grails - 域类中的继承 - 将列继承到基表中

Question

I have a Record class as:

class Record {
    Date dateCreated
    Date lastUpdated
    def beforeInsert() {
        dateCreated = new Date()
    }
    def beforeUpdate() {
        lastUpdated = new Date()
    }
    static mapping = { tablePerHierarchy false }
}

And this class is inherited by several other domain classes - for example:

class User extends Record{
    String userName
    String password
    String email
}

My question here is: Is there any way to embedd the columns of Record table into the table which extends it?

Answer 1

You can define tablePerClass or tablePerHierarchy strategies. See documentation here .

So, following, your code you should use:

static mapping = {
    tablePerHierarchy true
}    

Answer 2

You could use inheritance here, however that might restrict your class hierarchy. I'm not as familiar with GORM as i am with straight hibernate (which is what GORM uses). If you find you want to use composition instead of inheritance, i believe something like this would work (i haven't tried it though):

@Embeddable class AuditTimestamps { ... }

class User {
   @Embedded AuditTimestamps auditTimestamps

   def beforeInsert() { auditTimestamps.beforeInsert() }
   def beforeUpdate() { auditTimestamps.beforeUpdate() }

}

I've done something exactly like this is straight java/hibernate and it works like a charm.

Answer 3

First thing is first, You don't need a brilliance here if your problem is dataCreated and dateUpdated, You could just put those fields where ever in the domain and GORM magically fills them out! If your plan is to not add them everywhere, you could simply create a Groovy class in src/groovy directory and then inherit those!

If you have a complex inheritance tree, then injecting those properties dynamical could be a solution too! You can do this in bootstrap!

def grailsApplication // Autowiring

grailsApplication.domainClasses.each { domainClass -> 
    // add the fields you want to the metaclass
}

If you plan to temper with the data before update and insert then override the beforeInsert and beforeUpdate methods. The drawback of overriding those methods from metaClass is that you cannot use them in the actual domain Classes.

The third way to do this is use custom eventListners and handling GORM(Hibernate) events.For details you should checkout here , the author is demonstrating how to do it from a plugin. Am sure you can map it to suit your use.