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Initial version of MigrationOptimizer and tests

This commit is contained in:
Andrew Godwin 2013-10-02 17:33:41 +01:00
parent 75bb6ba966
commit a80d9ab0fe
5 changed files with 237 additions and 0 deletions
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13
django/db/migrations/operations/base.py
View File

@ -63,3 +63,16 @@ class Operation(object):
Outputs a brief summary of what the action does.
"""
return "%s: %s" % (self.__class__.__name__, self._constructor_args)
def __repr__(self):
return "<%s %s%s>" % (
self.__class__.__name__,
", ".join(map(repr, self._constructor_args[0])),
",".join(" %s=%r" % x for x in self._constructor_args[1].items()),
)
def __eq__(self, other):
return (self.__class__ == other.__class__) and (self.deconstruct() == other.deconstruct())
def __ne__(self, other):
return not (self == other)

16
django/db/migrations/operations/fields.py
View File

@ -29,6 +29,14 @@ class AddField(Operation):
def describe(self):
return "Add field %s to %s" % (self.name, self.model_name)
def __eq__(self, other):
return (
(self.__class__ == other.__class__) and
(self.name == other.name) and
(self.model_name == other.model_name) and
(self.field.deconstruct()[1:] == other.field.deconstruct()[1:])
)
class RemoveField(Operation):
"""
@ -92,6 +100,14 @@ class AlterField(Operation):
def describe(self):
return "Alter field %s on %s" % (self.name, self.model_name)
def __eq__(self, other):
return (
(self.__class__ == other.__class__) and
(self.name == other.name) and
(self.model_name == other.model_name) and
(self.field.deconstruct()[1:] == other.field.deconstruct()[1:])
)
class RenameField(Operation):
"""

9
django/db/migrations/operations/models.py
View File

@ -32,6 +32,15 @@ class CreateModel(Operation):
def describe(self):
return "Create model %s" % (self.name, )
def __eq__(self, other):
return (
(self.__class__ == other.__class__) and
(self.name == other.name) and
(self.options == other.options) and
(self.bases == other.bases) and
([(k, f.deconstruct()[1:]) for k, f in self.fields] == [(k, f.deconstruct()[1:]) for k, f in other.fields])
)
class DeleteModel(Operation):
"""

104
django/db/migrations/optimizer.py Normal file
View File

@ -0,0 +1,104 @@
from django.db import migrations
class MigrationOptimizer(object):
"""
Powers the optimization process, where you provide a list of Operations
and you are returned a list of equal or shorter length - operations
are merged into one if possible.
For example, a CreateModel and an AddField can be optimised into a
new CreateModel, and CreateModel and DeleteModel can be optimised into
nothing.
"""
def optimize(self, operations):
"""
Main optimization entry point. Pass in a list of Operation instances,
get out a new list of Operation instances.
Unfortunately, due to the scope of the optimisation (two combinable
operations might be separated by several hundred others), this can't be
done as a peephole optimisation with checks/output implemented on
the Operations themselves; instead, the optimizer looks at each
individual operation and scans forwards in the list to see if there
are any matches, stopping at boundaries - operations which can't
be optimized over (RunSQL, operations on the same field/model, etc.)
The inner loop is run until the starting list is the same as the result
list, and then the result is returned. This means that operation
optimization must be stable and always return an equal or shorter list.
"""
# Internal tracking variable for test assertions about # of loops
self._iterations = 0
while True:
result = self.optimize_inner(operations)
self._iterations += 1
if result == operations:
return result
operations = result
def optimize_inner(self, operations):
"""
Inner optimization loop.
"""
new_operations = []
for i, operation in enumerate(operations):
# Compare it to each operation after it
for j, other in enumerate(operations[i+1:]):
result = self.reduce(operation, other)
if result is not None:
# Optimize! Add result, then remaining others, then return
new_operations.extend(result)
new_operations.extend(operations[i+1:i+1+j])
new_operations.extend(operations[i+j+2:])
return new_operations
if not self.can_optimize_through(operation, other):
new_operations.append(operation)
break
else:
new_operations.append(operation)
return new_operations
#### REDUCTION ####
def reduce(self, operation, other):
"""
Either returns a list of zero, one or two operations,
or None, meaning this pair cannot be optimized.
"""
submethods = [
(migrations.CreateModel, migrations.DeleteModel, self.reduce_model_create_delete),
(migrations.AlterModelTable, migrations.DeleteModel, self.reduce_model_alter_delete),
(migrations.AlterUniqueTogether, migrations.DeleteModel, self.reduce_model_alter_delete),
(migrations.AlterIndexTogether, migrations.DeleteModel, self.reduce_model_alter_delete),
]
for ia, ib, om in submethods:
if isinstance(operation, ia) and isinstance(other, ib):
return om(operation, other)
return None
def reduce_model_create_delete(self, operation, other):
"""
Folds a CreateModel and a DeleteModel into nothing.
"""
if operation.name == other.name:
return []
return None
def reduce_model_alter_delete(self, operation, other):
"""
Folds an AlterModelSomething and a DeleteModel into nothing.
"""
if operation.name == other.name:
return [other]
return None
#### THROUGH CHECKS ####
def can_optimize_through(self, operation, other):
"""
Returns True if it's possible to optimize 'operation' with something
the other side of 'other'. This is possible if, for example, they
affect different models.
"""
return False

95
tests/migrations/test_optimizer.py Normal file
View File

@ -0,0 +1,95 @@
# encoding: utf8
import operator
from django.test import TestCase
from django.db.migrations.optimizer import MigrationOptimizer
from django.db import migrations
from django.db import models
class OptimizerTests(TestCase):
"""
Tests the migration autodetector.
"""
def optimize(self, operations):
"""
Handy shortcut for getting results + number of loops
"""
optimizer = MigrationOptimizer()
return optimizer.optimize(operations), optimizer._iterations
def assertOptimizesTo(self, operations, expected, exact=None, less_than=None):
result, iterations = self.optimize(operations)
self.assertEqual(expected, result)
if exact is not None and iterations != exact:
raise self.failureException("Optimization did not take exactly %s iterations (it took %s)" % (exact, iterations))
if less_than is not None and iterations >= less_than:
raise self.failureException("Optimization did not take less than %s iterations (it took %s)" % (less_than, iterations))
def test_operation_equality(self):
"""
Tests the equality operator on lists of operations.
If this is broken, then the optimizer will get stuck in an
infinite loop, so it's kind of important.
"""
self.assertEqual(
[migrations.DeleteModel("Test")],
[migrations.DeleteModel("Test")],
)
self.assertEqual(
[migrations.CreateModel("Test", [("name", models.CharField(max_length=255))])],
[migrations.CreateModel("Test", [("name", models.CharField(max_length=255))])],
)
self.assertNotEqual(
[migrations.CreateModel("Test", [("name", models.CharField(max_length=255))])],
[migrations.CreateModel("Test", [("name", models.CharField(max_length=100))])],
)
self.assertEqual(
[migrations.AddField("Test", "name", models.CharField(max_length=255))],
[migrations.AddField("Test", "name", models.CharField(max_length=255))],
)
self.assertNotEqual(
[migrations.AddField("Test", "name", models.CharField(max_length=255))],
[migrations.AddField("Test", "name", models.CharField(max_length=100))],
)
self.assertNotEqual(
[migrations.AddField("Test", "name", models.CharField(max_length=255))],
[migrations.AlterField("Test", "name", models.CharField(max_length=255))],
)
def test_single(self):
"""
Tests that the optimizer does nothing on a single operation,
and that it does it in just one pass.
"""
self.assertOptimizesTo(
[migrations.DeleteModel("Foo")],
[migrations.DeleteModel("Foo")],
exact = 1,
)
def test_create_delete_model(self):
"""
CreateModel and DeleteModel should collapse into nothing.
"""
self.assertOptimizesTo(
[
migrations.CreateModel("Foo", [("name", models.CharField(max_length=255))]),
migrations.DeleteModel("Foo"),
],
[],
)
def test_create_alter_delete_model(self):
"""
CreateModel, AlterModelTable, AlterUniqueTogether, and DeleteModel should collapse into nothing.
"""
self.assertOptimizesTo(
[
migrations.CreateModel("Foo", [("name", models.CharField(max_length=255))]),
migrations.AlterModelTable("Foo", "woohoo"),
migrations.AlterUniqueTogether("Foo", [["a", "b"]]),
migrations.DeleteModel("Foo"),
],
[],
)