A Grails many-to-many needs a hasMany on each side but one of them also needs a belongsTo to define the owning side. Ordinarily if you omit the belongsTo Grails complains at startup but it doesn't in this case; I'm assuming it's because as of 2.0 there is a real "errors" property (the validation Errors instance) in each domain class, so it's not considering this a proper many-to-many. If you change "errors" to "errs" you will see the startup message.
When trying to work with legacy database it's convenient to run 'grails schema-export' and look at the generated target/ddl.sql file. Keep tweaking the mappings and comparing the generated DDL to the real database until they're equivalent.
Btw - you should remove the semicolons from your code, and also the "Long id" fields since Grails adds those for you.
Burt
meena wrote
I have many-to-many between two existing tables(Error and Attribute) with the joint table(Error_Attribute_Map) in database. I am trying to map them using domain classes. Problem I am facing is when I ask for Attribute from Error GORM query does not include Joint Table hence I dont get back any Attribute Objects for a given Error Object. Please let me know If I am missing any mapping.
Error domain class
class Error {
Long id;
String comment;
static hasMany = [attributes:Attribute]
static constraints = {
id()
comment()
}
static mapping = {
table('error')
id(generator:'identity',name:'id',column:'error_id')
attributes(joinTable:[name:'ERROR_ATTRIBUTE_MAP',key:'error_id', column:'attribute_id'])
}
}
Attribute domain class
class Attribute {
Long id;
String attribute;
static hasMany = [errors:Error]
static constraints = {
}
static mapping = {
table('ATTRIBUTE')
id(generator:'identity',name:'id',column:'attribute_id')
errors(joinTable:[name:'ERROR_ATTRIBUTE_MAP',key:'attribute_id', column:'error_id'])
}
}
Error_Attribute_Map table in Database
34 CREATE TABLE `ERROR_ATTRIBUTE_MAP` (
`error_id` int(10) unsigned NOT NULL default '0',
`attribute_id` int(10) unsigned NOT NULL default '0',
KEY `error_id` (`error_id`),
KEY `attribute_id` (`attribute_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
when I ask
error.attributes
query made by Grails is
select
attributes0_.error_id as error6_3_1_,
attributes0_.attribute_id as attribute1_1_,
attributes0_.attribute_id as attribute1_2_0_,
attributes0_.version as version2_0_,
attributes0_.attribute as attribute2_0_,
from
ATTRIBUTE attributes0_
where
attributes0_.error_id=?
Locked
