I have two domain-classes. One is a "Partner" the other is a "Customer". A customer can be a part of a Partner and a Partner can have 1 or more Customers:

class Customer {
    Integer id
    String name
    static hasOne = [partner:Partner]
    static mapping = {
        partner joinTable:[name:'PartnerMap',column:'partner_id',key:'customer_id']
    }
}

class Partner {
    Integer id
    static hasMany = [customers:Customer]
    static mapping = {
        customers joinTable:[name:'PartnerMap',column:'customer_id',key:'partner_id']
    }
}

However, whenever I try to see if a customer is a part of a partner, like this:

def customers = Customer.list()
customers.each {
     if (it.partner) {
          println "Partner!"
     }
}

I get the following error:

org.springframework.dao.InvalidDataAccessResourceUsageException: could not execute query; SQL [select this_.customer_id as customer1_162_0_, this_.company as company162_0_, this_.display_name as display3_162_0_, this_.parent_customer_id as parent4_162_0_, this_.partner_id as partner5_162_0_, this_.server_id as server6_162_0_, this_.status as status162_0_, this_.vertical_market as vertical8_162_0_ from Customer this_]; nested exception is org.hibernate.exception.SQLGrammarException: could not execute query

It looks as if Grails is thinking partner_id is a part of the Customer query, and it's not... It is in the PartnerMap table, which is supposed to find the customer_id, then get the Partner from the corresponding partner_id.

Anyone have any clue what I'm doing wrong?

Edit: I forgot to mention I'm doing this with legacy database tables. So I have a Partner, Customer and PartnerMap table. PartnerMap has simply a customer_id and partner_id field.