GORM and Composite Keys in associations - grails

Question

I have legacy database and some tables have composite ids
class Client {
String id
static hasMany = [
settings: Setting
]
static mapping = {
id column: 'client_id', generator: 'assigned'
}
}
class Setting {
Client client
String nodeId
String ccyPairPattern
Character qualifier
static mapping = {
id composite: ['client', 'nodeId', 'pattern', 'qualifier']
}
}
I want to delete entry from GORM association:
client.get('1').removeFromSettings(settingToRemove)
// settingToRemove.delete(flush: true)
// delete-orphans does not help
This always raises exception after flush
org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect) :
This happens because method removeFrom* sets client property to null and generates query to delete with clientId = null as client is part of composite key
What is the best solution in this case. Looks like GORM has poor support for composite keys or my mapping is incorrect.

Answer 1

When you use hasMany without a belongsTo on the many side, in other words a unidirectional association, you get a join table. For example...
class PurchaseOrder {
static hasMany = [items: Item]
}
class Item { }
Would yield three database tables: purchase_order, item, and purchase_order_items. The purchase_order_items table would contain two columns: purchase_order_id and item_id. You can read more about join tables here.
Since you're dealing with a legacy database, I think the best solution is not to use addTo*() and removeFrom*().
Ensure you don't have a join table. If you have a join table, remove the hasMany association.
You'll need to add/remove Setting instances manually.
Example:
def client = Client.get(1)
// Adding a setting
def setting = new Setting(client: client, nodeId: blah...)
setting.save()
// Removing a setting
/*
The prototype is used to search for a domain instance with a composite primary key.
So simply set the composite key properties accordingly.
*/
def prototype = new Setting(client: client, nodeId: blah...)
def setting = Setting.get(prototype)
setting.delete()
Lacking a hasMany association, you won't be able to access a client's settings via the client.settings property. Instead you'd have to query for them like this:
def settings = Setting.findByClient(client)
A consequence of using a legacy database is that if the database doesn't align with that GORM/Hibernate expects it will be limited in what it can do for you.