#25105: Migrating multiple CharFields to null=False breaks on PostgreSQL
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Reporter: danielr | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: 1.8
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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Given a model containing multiple CharFields defined as {{{null=True}}},
and at least one row with null data in two or more of those fields, then
change the CharFields to null=False and create a migration with a
temporary default of the empty string.
Running this migration will attempt, for each field, to set the null
values to the empty string, then migrate the field to NOT NULL. However,
the second field will fail with the error {{{psycopg2.OperationalError:
cannot ALTER TABLE "fundraising_donation" because it has pending trigger
events}}}.
Clearly this is the same issue warned against in the
[https://docs.djangoproject.com/en/1.8/ref/migration-operations/#runpython
migration documentation] as caused by mixing RunPython and schema changes
in the same migration; however, here it is a fully automatically-generated
migration which causes the error.
Some possible solutions:
* Do nothing but mention this edge case in the documentation;
* Detect and warn against converting multiple null=False fields in one
migration;
* Detect and deal with the problem in some way, perhaps by committing the
transaction after each field.
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Ticket URL: <https://code.djangoproject.com/ticket/25105>
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