Grails中的多对多关系

Question

I am writing a basic web application with grails using hibernate w/ MySQL and vaadin, spring security, and spring security acl plugins that is used to manage Committees, Members, and memberships between Committees and Members. All of the CRUD works for both Members and Committees, but when I create a CommitteeMember object, it has trouble referencing the Member field of the class to get information about the member involved in the membership. Here are my classes:

class Committee {
    String name
    String description
    String bylaws
    static hasMany = [members: CommitteeMember]
    static constraints = {
        name blank: false, nullable: false, matches: "[a-zA-Z0-9 ]*", unique: true
        description blank: false, nullable: false, matches: "[a-zA-Z0-9 ]*"
        bylaws blank: false, nullable: false, matches: "[a-zA-Z0-9 ]*"
   }
}

class Member {
    String firstName
    String middleName
    String lastName
    String address
    String phone

    static hasMany = [committees: CommitteeMember]
    static constraints = {
        firstName blank: false, nullable: false, matches: "[a-zA-Z]*"
        middleName blank: false, nullable: false, matches: "[a-zA-Z]*"
        lastName blank: false, nullable: false, matches: "[a-zA-Z]*"
        address blank: false, nullable: false, matches: "[0-9a-zA-Z ]*"
        phone blank: false, nullable: false, minSize: 10, maxSize: 10, matches: "[0-9]*"
    }
}

class CommitteeMember {

    Member member
    Committee committee
    Date startDate
    Date endDate
    String title
    Date created = new Date()
    Date updated = new Date()

    static constraints = {
        startDate blank: false, nullable: false, format: 'mm/dd/yyyy'
        endDate blank: false, nullable: false, format: 'mm/dd/yyyy'
        title blank: false, nullable: false, matches: "[a-zA-Z0-9 ]*"
        created blank: false, nullable: false, editable: false, display: false
        updated blank: false, nullable: false, editable: false, display: false
    }

}

And the methods of the service layer that add these classes:

@Transactional
def saveCommittee(name, desc, bylaws) {
    new Committee(name: name, description: desc, bylaws: bylaws).save(flush: true);
}

@Transactional
def saveMember(fname, mname, lname, address, phone) {
    new Member(firstName: fname, middleName: mname, lastName: lname,
                 address: address, phone: phone).save(flush: true);
}

@Transactional
def saveCommitteeMember(cname, lname, fname, title, start, end) {
    def cmem = new CommitteeMember(title: title, startDate: start, endDate: end);
    cmem.member = Member.findByLastNameAndFirstName(lname, fname);
    cmem.committee = Committee.findByName(cname);
    cmem.save(flush: true);
}

Creating these classes works, and they are stored in the database. My update and delete methods work great for the members and the committees. But, when I try to something like

//this works
def cm = CommitteeMember.get(1);
def title = cm.title;

//this does not
def firstName = cm.member.firstName;

none of the fields of the Member referenced by the Committee member are accessible. What am I doing wrong here? I've done lots of research and can't find anything exactly like this. Help would be GREATLY appreciated. Pulling my hair out over this thing..

**UPDATE

In the service layer method saveCommitteeMember() , I added a line println(cmem.member.firstName); , and in the terminal where my grails is launching, it indeed does print the first name of the member that I added to a committee when I call the function.

Answer 1

JESUS. I finally figured it out. Ok, here it what was happening. Hibernate does findByFirstNameAndLastName() , and that works fine, but since grails is LAZY by default, it only returns a REFERENCE to that Member object, and not an object representation of the data within the table. This reference is destroyed when the function returns, and the CommitteeMember object is left with its member field pointing to nothing. This is especially great, because using the Vaadin plugin, you don't get the LazyInitializationException - no session exists or whatever that error message is unless you are explicitly trying to reference something from a @Transaction, so doing def fname = cm.member.firstName wasn't throwing said exception, because the @Transaction was thought of as a success, and I was simply trying to read a null value, which resulted in no error message whatsoever other than termination of the function in which the error occurred. Talk about some serious bull#$&%!

Anyways, to FIX this ridiculous issue, add this to the objects you are having null issues with

class CommitteeMember {

    Member member
    Committee committee
    etc......

    static mapping = {
        member lazy: false
        committee lazy: false
    }

}

I REALLY hope that anyone else who has a problem like this finds this post. This has cost me loads of time on something so ridiculous. Lazy evaluation is super nice in some situations. Database operations, IMO, are not those type of situations. Anyways, cheers.