#19385: Add support for multiple-column join
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Reporter: cseibert | Owner: nobody
Type: New feature | Status: new
Component: Database layer | Version: 1.4
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: join | Needs documentation: 0
Has patch: 1 | Patch needs improvement: 1
Needs tests: 0 | UI/UX: 0
Easy pickings: 0 |
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Comment (by akaariai):
The names_to_path_to_fields stuff is in master now.
I think the next step is the possibility to have multiple columns per
join, then try to fix all the possible places which break under
multicolumn joins in the ORM. Here is a partial list:
- IN lookups
- What other lookups to support and how to do this
- Subquery support (we should use EXISTS instead of IN subqueries)
- Join trimming
- Representation of the foreign key in the model's _meta.
I am sure I am missing half of the complications.
I think we will want to abandon the get_join_clause() approach. This means
there will be too little information available in the ORM, and we would
need to move stuff like "can we trim this join" into fields which doesn't
seem right. However, we will likely want to support the case of _no_ join
columns, so that one can generate the whole clause in the
field.get_extra_join_sql(). (Also, we might want to reconsider the name
AND implementation of the get_extra_join_sql() method before 1.6...)
It seems the work done in
https://github.com/jtillman/django/compare/ticket_19385 is a good basis
for doing further work on the ORM changes. We should also see what
koniiiik has done so that we won't be duplicating or invalidating his work
here.
--
Ticket URL: <https://code.djangoproject.com/ticket/19385#comment:18>
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