String IDs in grails - how exactly can it be done?

Can somebody show me clear, complete, 100% working way to set string-typed field 开发者_如何学Pythonas ID in grails? I've read the docs, then read all similar ranting on the web, but failed to create a working prototype.

Here is one of my attempts to make you believe I'm not just lazily waiting for somebody to do the job )))

    class User {
  String login
  static hasMany = [apps : Application]

  static constraints = { 
  }

  static mapping = { 
    id generator: 'assigned', name: "login"
  }

}

When you use a natural id you have to use the findBy method instead of the get method as demonstrated in this test:

def user = new User(login: "test")
assertNotNull user.save(flush: true)

user = User.findByLogin("test")
assertNotNull user
assertEquals "test", user.login

Alternately you could use a single field composite id mapping:

class User implements Serializable {
    String login

    static hasMany = [apps: Application]

    static constraints = {
    }

    static mapping = {
        id composite: ['login']
    }
}

Note that composite id domain classes are required to implement Serializable.

The test for the composite id would be:

def user = new User(login: "test")
assertNotNull user.save(flush: true)

user = User.get(new User(login: "test"))
assertNotNull user
assertEquals "test", user.login

I'm assuming you are talking about mapping a String primary key (normally a natural key) to the primary key in a grails domain object.

This answer is derived from information found here: http://dsommerville.blogspot.com/2009/09/mapping-natural-keys-using-gorm.html and here: http://gr8fanboy.wordpress.com/2010/04/08/adding-a-natural-key-to-a-database-table-using-straight-gorm/

For example, you have a table Users defined with the following schema:

username    varchar(40) not null pimary key,
firstname   varchar(40) not null,
lastname    varchar(40) not null

To do this in grails, you have to massage the definition a little.' First, you have to map the id to the given column in your database. With a generator "assigned"

Then, for usability, you may want to add the transient field username so that you can use user.username = . Otherwise, I believe you'd have to access the field using id. The getter and setter for this transient property set the appropriate "id" field, which in turn updates the database.

class User {
  String id
  String password
  String fullName

  static transients = ['username']

  static constraints = {
    id(unique:true,blank:false)
    password(nullable:true,maxSize:20)
    fullName(nullable:true,maxSize:20)
  }

  static mapping = {
    table 'users'
    id column: 'username', generator: 'assigned'
    version false
  }

  //
  void setUsername(String username) {
    id = username
  }

  String getUsername() {
    return id
  }
}

Note: Scaffolding doesn't recognize the transient field, so you'll have to work the generated controllers/views if you want your code to more closely model your db.