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from __future__ import unicode_literals
from django.apps.registry import apps as global_apps
from django.db import migrations
from .loader import MigrationLoader
from .recorder import MigrationRecorder
from .state import ProjectState
class MigrationExecutor(object):
"""
End-to-end migration execution - loads migrations, and runs them
up or down to a specified set of targets.
"""
def __init__(self, connection, progress_callback=None):
self.connection = connection
self.loader = MigrationLoader(self.connection)
self.recorder = MigrationRecorder(self.connection)
self.progress_callback = progress_callback
def migration_plan(self, targets, clean_start=False):
"""
Given a set of targets, returns a list of (Migration instance, backwards?).
"""
plan = []
if clean_start:
applied = set()
else:
applied = set(self.loader.applied_migrations)
for target in targets:
# If the target is (app_label, None), that means unmigrate everything
if target[1] is None:
for root in self.loader.graph.root_nodes():
if root[0] == target[0]:
for migration in self.loader.graph.backwards_plan(root):
if migration in applied:
plan.append((self.loader.graph.nodes[migration], True))
applied.remove(migration)
# If the migration is already applied, do backwards mode,
# otherwise do forwards mode.
elif target in applied:
# Don't migrate backwards all the way to the target node (that
# may roll back dependencies in other apps that don't need to
# be rolled back); instead roll back through target's immediate
# child(ren) in the same app, and no further.
next_in_app = sorted(
n for n in
self.loader.graph.dependents.get(target, set())
if n[0] == target[0]
)
for node in next_in_app:
for migration in self.loader.graph.backwards_plan(node):
if migration in applied:
plan.append((self.loader.graph.nodes[migration], True))
applied.remove(migration)
else:
for migration in self.loader.graph.forwards_plan(target):
if migration not in applied:
plan.append((self.loader.graph.nodes[migration], False))
applied.add(migration)
return plan
def migrate(self, targets, plan=None, fake=False):
"""
Migrates the database up to the given targets.
Django first needs to create all project states before a migration is
(un)applied and in a second step run all the database operations.
"""
if plan is None:
plan = self.migration_plan(targets)
migrations_to_run = {m[0] for m in plan}
# Create the forwards plan Django would follow on an empty database
full_plan = self.migration_plan(self.loader.graph.leaf_nodes(), clean_start=True)
# Holds all states right before and right after a migration is applied
# if the migration is being run.
states = {}
state = ProjectState(real_apps=list(self.loader.unmigrated_apps))
if self.progress_callback:
self.progress_callback("render_start")
state.apps # Render all real_apps -- performance critical
if self.progress_callback:
self.progress_callback("render_success")
# Phase 1 -- Store all required states
for migration, _ in full_plan:
if migration in migrations_to_run:
states[migration] = state.clone()
state = migration.mutate_state(state) # state is cloned inside
# Phase 2 -- Run the migrations
for migration, backwards in plan:
if not backwards:
self.apply_migration(states[migration], migration, fake=fake)
else:
self.unapply_migration(states[migration], migration, fake=fake)
def collect_sql(self, plan):
"""
Takes a migration plan and returns a list of collected SQL
statements that represent the best-efforts version of that plan.
"""
statements = []
state = None
for migration, backwards in plan:
with self.connection.schema_editor(collect_sql=True) as schema_editor:
if state is None:
state = self.loader.project_state((migration.app_label, migration.name), at_end=False)
if not backwards:
state = migration.apply(state, schema_editor, collect_sql=True)
else:
state = migration.unapply(state, schema_editor, collect_sql=True)
statements.extend(schema_editor.collected_sql)
return statements
def apply_migration(self, state, migration, fake=False):
"""
Runs a migration forwards.
"""
if self.progress_callback:
self.progress_callback("apply_start", migration, fake)
if not fake:
# Test to see if this is an already-applied initial migration
applied, state = self.detect_soft_applied(state, migration)
if applied:
fake = True
else:
# Alright, do it normally
with self.connection.schema_editor() as schema_editor:
state = migration.apply(state, schema_editor)
# For replacement migrations, record individual statuses
if migration.replaces:
for app_label, name in migration.replaces:
self.recorder.record_applied(app_label, name)
else:
self.recorder.record_applied(migration.app_label, migration.name)
# Report progress
if self.progress_callback:
self.progress_callback("apply_success", migration, fake)
return state
def unapply_migration(self, state, migration, fake=False):
"""
Runs a migration backwards.
"""
if self.progress_callback:
self.progress_callback("unapply_start", migration, fake)
if not fake:
with self.connection.schema_editor() as schema_editor:
state = migration.unapply(state, schema_editor)
# For replacement migrations, record individual statuses
if migration.replaces:
for app_label, name in migration.replaces:
self.recorder.record_unapplied(app_label, name)
else:
self.recorder.record_unapplied(migration.app_label, migration.name)
# Report progress
if self.progress_callback:
self.progress_callback("unapply_success", migration, fake)
return state
def detect_soft_applied(self, project_state, migration):
"""
Tests whether a migration has been implicitly applied - that the
tables it would create exist. This is intended only for use
on initial migrations (as it only looks for CreateModel).
"""
# Bail if the migration isn't the first one in its app
if [name for app, name in migration.dependencies if app == migration.app_label]:
return False, project_state
if project_state is None:
after_state = self.loader.project_state((migration.app_label, migration.name), at_end=True)
else:
after_state = migration.mutate_state(project_state)
apps = after_state.apps
found_create_migration = False
# Make sure all create model are done
for operation in migration.operations:
if isinstance(operation, migrations.CreateModel):
model = apps.get_model(migration.app_label, operation.name)
if model._meta.swapped:
# We have to fetch the model to test with from the
# main app cache, as it's not a direct dependency.
model = global_apps.get_model(model._meta.swapped)
if model._meta.db_table not in self.connection.introspection.table_names(self.connection.cursor()):
return False, project_state
found_create_migration = True
# If we get this far and we found at least one CreateModel migration,
# the migration is considered implicitly applied.
return found_create_migration, after_state
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