#22325: Defining a custom user model in an app and having relations between it
and
other models in the app causes circular dependencies
----------------------------+--------------------------------------
Reporter: melinath | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: master
Severity: Normal | Resolution:
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by nliberg):
As far as I can see the error is in the `build_graph` method of the
`MigrationLoader` class.
The `self.graph.root_nodes(...)` method seems to be invoked before the
graph is fully built resulting in some extra nodes in the returned set
that are root nodes in the current partial graph but are not root nodes in
the final graph. Since the parent of the dependency relationship is drawn
from this set of nodes one can end up with an incorrect loop from the node
to itself in the graph. This results in a CircularDependencyError
exception at a later stage.
The problem seem to be fixed by building the graph in two steps: first
handling all normal nodes and then the `"__first__"` nodes (that get
remapped to a root node). Someone with a deeper understanding of the
relevant code will have to be the judge of whether this is a partial or
complete fix. At least the patch above fixes the problem for me.
--
Ticket URL: <https://code.djangoproject.com/ticket/22325#comment:2>
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