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Initial version of MigrationOptimizer and tests
This commit is contained in:
Andrew Godwin
@@ -63,3 +63,16 @@ class Operation(object):
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Outputs a brief summary of what the action does.
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"""
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return "%s: %s" % (self.__class__.__name__, self._constructor_args)
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def __repr__(self):
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return "<%s %s%s>" % (
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self.__class__.__name__,
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", ".join(map(repr, self._constructor_args[0])),
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",".join(" %s=%r" % x for x in self._constructor_args[1].items()),
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)
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def __eq__(self, other):
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return (self.__class__ == other.__class__) and (self.deconstruct() == other.deconstruct())
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def __ne__(self, other):
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return not (self == other)
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@@ -29,6 +29,14 @@ class AddField(Operation):
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def describe(self):
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return "Add field %s to %s" % (self.name, self.model_name)
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def __eq__(self, other):
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return (
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(self.__class__ == other.__class__) and
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(self.name == other.name) and
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(self.model_name == other.model_name) and
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(self.field.deconstruct()[1:] == other.field.deconstruct()[1:])
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)
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class RemoveField(Operation):
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"""
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@@ -92,6 +100,14 @@ class AlterField(Operation):
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def describe(self):
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return "Alter field %s on %s" % (self.name, self.model_name)
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def __eq__(self, other):
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return (
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(self.__class__ == other.__class__) and
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(self.name == other.name) and
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(self.model_name == other.model_name) and
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(self.field.deconstruct()[1:] == other.field.deconstruct()[1:])
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)
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class RenameField(Operation):
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"""
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@@ -32,6 +32,15 @@ class CreateModel(Operation):
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def describe(self):
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return "Create model %s" % (self.name, )
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def __eq__(self, other):
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return (
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(self.__class__ == other.__class__) and
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(self.name == other.name) and
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(self.options == other.options) and
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(self.bases == other.bases) and
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([(k, f.deconstruct()[1:]) for k, f in self.fields] == [(k, f.deconstruct()[1:]) for k, f in other.fields])
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)
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class DeleteModel(Operation):
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"""
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104
django/db/migrations/optimizer.py
Normal file
104
django/db/migrations/optimizer.py
Normal file
@@ -0,0 +1,104 @@
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from django.db import migrations
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class MigrationOptimizer(object):
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"""
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Powers the optimization process, where you provide a list of Operations
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and you are returned a list of equal or shorter length - operations
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are merged into one if possible.
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For example, a CreateModel and an AddField can be optimised into a
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new CreateModel, and CreateModel and DeleteModel can be optimised into
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nothing.
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"""
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def optimize(self, operations):
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"""
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Main optimization entry point. Pass in a list of Operation instances,
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get out a new list of Operation instances.
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Unfortunately, due to the scope of the optimisation (two combinable
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operations might be separated by several hundred others), this can't be
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done as a peephole optimisation with checks/output implemented on
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the Operations themselves; instead, the optimizer looks at each
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individual operation and scans forwards in the list to see if there
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are any matches, stopping at boundaries - operations which can't
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be optimized over (RunSQL, operations on the same field/model, etc.)
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The inner loop is run until the starting list is the same as the result
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list, and then the result is returned. This means that operation
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optimization must be stable and always return an equal or shorter list.
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"""
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# Internal tracking variable for test assertions about # of loops
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self._iterations = 0
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while True:
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result = self.optimize_inner(operations)
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self._iterations += 1
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if result == operations:
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return result
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operations = result
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def optimize_inner(self, operations):
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"""
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Inner optimization loop.
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"""
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new_operations = []
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for i, operation in enumerate(operations):
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# Compare it to each operation after it
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for j, other in enumerate(operations[i+1:]):
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result = self.reduce(operation, other)
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if result is not None:
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# Optimize! Add result, then remaining others, then return
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new_operations.extend(result)
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new_operations.extend(operations[i+1:i+1+j])
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new_operations.extend(operations[i+j+2:])
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return new_operations
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if not self.can_optimize_through(operation, other):
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new_operations.append(operation)
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break
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else:
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new_operations.append(operation)
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return new_operations
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#### REDUCTION ####
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def reduce(self, operation, other):
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"""
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Either returns a list of zero, one or two operations,
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or None, meaning this pair cannot be optimized.
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"""
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submethods = [
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(migrations.CreateModel, migrations.DeleteModel, self.reduce_model_create_delete),
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(migrations.AlterModelTable, migrations.DeleteModel, self.reduce_model_alter_delete),
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(migrations.AlterUniqueTogether, migrations.DeleteModel, self.reduce_model_alter_delete),
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(migrations.AlterIndexTogether, migrations.DeleteModel, self.reduce_model_alter_delete),
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]
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for ia, ib, om in submethods:
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if isinstance(operation, ia) and isinstance(other, ib):
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return om(operation, other)
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return None
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def reduce_model_create_delete(self, operation, other):
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"""
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Folds a CreateModel and a DeleteModel into nothing.
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"""
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if operation.name == other.name:
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return []
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return None
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def reduce_model_alter_delete(self, operation, other):
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"""
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Folds an AlterModelSomething and a DeleteModel into nothing.
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"""
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if operation.name == other.name:
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return [other]
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return None
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#### THROUGH CHECKS ####
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def can_optimize_through(self, operation, other):
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"""
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Returns True if it's possible to optimize 'operation' with something
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the other side of 'other'. This is possible if, for example, they
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affect different models.
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"""
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return False
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95
tests/migrations/test_optimizer.py
Normal file
95
tests/migrations/test_optimizer.py
Normal file
@@ -0,0 +1,95 @@
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# encoding: utf8
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import operator
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from django.test import TestCase
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from django.db.migrations.optimizer import MigrationOptimizer
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from django.db import migrations
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from django.db import models
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class OptimizerTests(TestCase):
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"""
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Tests the migration autodetector.
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"""
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def optimize(self, operations):
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"""
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Handy shortcut for getting results + number of loops
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"""
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optimizer = MigrationOptimizer()
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return optimizer.optimize(operations), optimizer._iterations
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def assertOptimizesTo(self, operations, expected, exact=None, less_than=None):
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result, iterations = self.optimize(operations)
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self.assertEqual(expected, result)
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if exact is not None and iterations != exact:
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raise self.failureException("Optimization did not take exactly %s iterations (it took %s)" % (exact, iterations))
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if less_than is not None and iterations >= less_than:
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raise self.failureException("Optimization did not take less than %s iterations (it took %s)" % (less_than, iterations))
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def test_operation_equality(self):
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"""
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Tests the equality operator on lists of operations.
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If this is broken, then the optimizer will get stuck in an
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infinite loop, so it's kind of important.
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"""
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self.assertEqual(
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[migrations.DeleteModel("Test")],
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[migrations.DeleteModel("Test")],
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)
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self.assertEqual(
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[migrations.CreateModel("Test", [("name", models.CharField(max_length=255))])],
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[migrations.CreateModel("Test", [("name", models.CharField(max_length=255))])],
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)
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self.assertNotEqual(
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[migrations.CreateModel("Test", [("name", models.CharField(max_length=255))])],
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[migrations.CreateModel("Test", [("name", models.CharField(max_length=100))])],
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)
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self.assertEqual(
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[migrations.AddField("Test", "name", models.CharField(max_length=255))],
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[migrations.AddField("Test", "name", models.CharField(max_length=255))],
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)
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self.assertNotEqual(
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[migrations.AddField("Test", "name", models.CharField(max_length=255))],
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[migrations.AddField("Test", "name", models.CharField(max_length=100))],
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)
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self.assertNotEqual(
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[migrations.AddField("Test", "name", models.CharField(max_length=255))],
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[migrations.AlterField("Test", "name", models.CharField(max_length=255))],
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)
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def test_single(self):
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"""
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Tests that the optimizer does nothing on a single operation,
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and that it does it in just one pass.
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"""
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self.assertOptimizesTo(
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[migrations.DeleteModel("Foo")],
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[migrations.DeleteModel("Foo")],
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exact = 1,
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)
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def test_create_delete_model(self):
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"""
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CreateModel and DeleteModel should collapse into nothing.
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"""
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self.assertOptimizesTo(
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[
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migrations.CreateModel("Foo", [("name", models.CharField(max_length=255))]),
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migrations.DeleteModel("Foo"),
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],
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[],
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)
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def test_create_alter_delete_model(self):
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"""
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CreateModel, AlterModelTable, AlterUniqueTogether, and DeleteModel should collapse into nothing.
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"""
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self.assertOptimizesTo(
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[
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migrations.CreateModel("Foo", [("name", models.CharField(max_length=255))]),
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migrations.AlterModelTable("Foo", "woohoo"),
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migrations.AlterUniqueTogether("Foo", [["a", "b"]]),
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migrations.DeleteModel("Foo"),
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],
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[],
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)
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