I'm using with Django 0.96 a custom Q object to make joins between
models, here's an example:
class Product(models.Model):
group = models.IntegerField() # primary key
code = models.CharField() # primary key
name = models.CharField()
...
class CartItem(models.Model):
product_group = models.IntegerField() # product foreign key
product_code = models.CharField() # product foreign key
quantity = models.IntegerField()
...
items = CartItem.objects.filter(
QJoin(Product, 'p', Q(group='product_group',
code='product_code'))).extra(
select={
'p.name': 'product__name'
})
for this to work i've translated this:
"Q(group='product_group', code='product_code')"
into this:
"ON (cartitem.product_group=p.group AND
cartitem.product_code=p.code)"
taking advantage of django.db.models.quey.Query._get_sql_clause
method:
if joins:
sql.append(" ".join(["%s %s %s ON %s" % (join_type, table,
alias, condition)
for (alias, (table, join_type, condition))
in joins.items()]))
Now on the new django.db.models.sql.query.BaseQuery i can add new
joins with the "join" method, but on "get_from_clause" the joins
construction does not allow me to construct a join on multiple
columns, here's the code from this method:
if join_type and not first:
result.append('%s %s%s ON (%s.%s = %s.%s)'
% (join_type, qn(name), alias_str, qn(lhs),
qn2(lhs_col), qn(alias), qn2(col)))
The solution i can think of is to subclass de BaseQuery and overwrite
the "get_from_clause" method.
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