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[1.7.x] Fixed #24110 -- Rewrote migration unapply to preserve intermediate states

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Backport of fdc2cc9487 and be158e3625 from master
This commit is contained in:
Markus Holtermann
2015-01-10 15:18:06 +01:00
parent 1a352fe175
commit ef5889409b
3 changed files with 45 additions and 26 deletions
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40
django/db/migrations/migration.py
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@@ -115,29 +115,39 @@ class Migration(object):
Takes a project_state representing all migrations prior to this one
and a schema_editor for a live database and applies the migration
in a reverse order.
The backwards migration process consists of two phases:
1. The intermediate states from right before the first until right
after the last operation inside this migration are preserved.
2. The operations are applied in reverse order using the states
recorded in step 1.
"""
# We need to pre-calculate the stack of project states
# Construct all the intermediate states we need for a reverse migration
to_run = []
new_state = project_state
# Phase 1
for operation in self.operations:
# If this operation cannot be represented as SQL, place a comment
# there instead
if collect_sql and not operation.reduces_to_sql:
schema_editor.collected_sql.append("--")
schema_editor.collected_sql.append("-- MIGRATION NOW PERFORMS OPERATION THAT CANNOT BE "
"WRITTEN AS SQL:")
schema_editor.collected_sql.append("-- %s" % operation.describe())
schema_editor.collected_sql.append("--")
continue
# If it's irreversible, error out
if not operation.reversible:
raise Migration.IrreversibleError("Operation %s in %s is not reversible" % (operation, self))
new_state = project_state.clone()
# Preserve new state from previous run to not tamper the same state
# over all operations
new_state = new_state.clone()
old_state = new_state.clone()
operation.state_forwards(self.app_label, new_state)
to_run.append((operation, project_state, new_state))
project_state = new_state
# Now run them in reverse
to_run.reverse()
to_run.insert(0, (operation, old_state, new_state))
# Phase 2
for operation, to_state, from_state in to_run:
if collect_sql:
if not operation.reduces_to_sql:
schema_editor.collected_sql.append("--")
schema_editor.collected_sql.append("-- MIGRATION NOW PERFORMS OPERATION THAT CANNOT BE "
"WRITTEN AS SQL:")
schema_editor.collected_sql.append("-- %s" % operation.describe())
schema_editor.collected_sql.append("--")
continue
if not schema_editor.connection.features.can_rollback_ddl and operation.atomic:
# We're forcing a transaction on a non-transactional-DDL backend
with atomic(schema_editor.connection.alias):