196 lines
8.3 KiB
Python
196 lines
8.3 KiB
Python
import os
|
|
from importlib import import_module
|
|
from django.utils.functional import cached_property
|
|
from django.db.models.loading import cache
|
|
from django.db.migrations.recorder import MigrationRecorder
|
|
from django.db.migrations.graph import MigrationGraph
|
|
from django.conf import settings
|
|
|
|
|
|
class MigrationLoader(object):
|
|
"""
|
|
Loads migration files from disk, and their status from the database.
|
|
|
|
Migration files are expected to live in the "migrations" directory of
|
|
an app. Their names are entirely unimportant from a code perspective,
|
|
but will probably follow the 1234_name.py convention.
|
|
|
|
On initialisation, this class will scan those directories, and open and
|
|
read the python files, looking for a class called Migration, which should
|
|
inherit from django.db.migrations.Migration. See
|
|
django.db.migrations.migration for what that looks like.
|
|
|
|
Some migrations will be marked as "replacing" another set of migrations.
|
|
These are loaded into a separate set of migrations away from the main ones.
|
|
If all the migrations they replace are either unapplied or missing from
|
|
disk, then they are injected into the main set, replacing the named migrations.
|
|
Any dependency pointers to the replaced migrations are re-pointed to the
|
|
new migration.
|
|
|
|
This does mean that this class MUST also talk to the database as well as
|
|
to disk, but this is probably fine. We're already not just operating
|
|
in memory.
|
|
"""
|
|
|
|
def __init__(self, connection):
|
|
self.connection = connection
|
|
self.disk_migrations = None
|
|
self.applied_migrations = None
|
|
|
|
@classmethod
|
|
def migrations_module(cls, app_label):
|
|
if app_label in settings.MIGRATION_MODULES:
|
|
return settings.MIGRATION_MODULES[app_label]
|
|
else:
|
|
return '%s.migrations' % cache.get_app_package(app_label)
|
|
|
|
def load_disk(self):
|
|
"""
|
|
Loads the migrations from all INSTALLED_APPS from disk.
|
|
"""
|
|
self.disk_migrations = {}
|
|
self.unmigrated_apps = set()
|
|
self.migrated_apps = set()
|
|
for app in cache.get_apps():
|
|
# Get the migrations module directory
|
|
app_label = app.__name__.split(".")[-2]
|
|
module_name = self.migrations_module(app_label)
|
|
try:
|
|
module = import_module(module_name)
|
|
except ImportError as e:
|
|
# I hate doing this, but I don't want to squash other import errors.
|
|
# Might be better to try a directory check directly.
|
|
if "No module named" in str(e) and "migrations" in str(e):
|
|
self.unmigrated_apps.add(app_label)
|
|
continue
|
|
raise
|
|
else:
|
|
# PY3 will happily import empty dirs as namespaces.
|
|
if not hasattr(module, '__file__'):
|
|
continue
|
|
# Module is not a package (e.g. migrations.py).
|
|
if not hasattr(module, '__path__'):
|
|
continue
|
|
self.migrated_apps.add(app_label)
|
|
directory = os.path.dirname(module.__file__)
|
|
# Scan for .py[c|o] files
|
|
migration_names = set()
|
|
for name in os.listdir(directory):
|
|
if name.endswith(".py") or name.endswith(".pyc") or name.endswith(".pyo"):
|
|
import_name = name.rsplit(".", 1)[0]
|
|
if import_name[0] not in "_.~":
|
|
migration_names.add(import_name)
|
|
# Load them
|
|
south_style_migrations = False
|
|
for migration_name in migration_names:
|
|
try:
|
|
migration_module = import_module("%s.%s" % (module_name, migration_name))
|
|
except ImportError as e:
|
|
# Ignore South import errors, as we're triggering them
|
|
if "south" in str(e).lower():
|
|
south_style_migrations = True
|
|
break
|
|
raise
|
|
if not hasattr(migration_module, "Migration"):
|
|
raise BadMigrationError("Migration %s in app %s has no Migration class" % (migration_name, app_label))
|
|
# Ignore South-style migrations
|
|
if hasattr(migration_module.Migration, "forwards"):
|
|
south_style_migrations = True
|
|
break
|
|
self.disk_migrations[app_label, migration_name] = migration_module.Migration(migration_name, app_label)
|
|
if south_style_migrations:
|
|
self.unmigrated_apps.add(app_label)
|
|
|
|
def get_migration(self, app_label, name_prefix):
|
|
"Gets the migration exactly named, or raises KeyError"
|
|
return self.graph.nodes[app_label, name_prefix]
|
|
|
|
def get_migration_by_prefix(self, app_label, name_prefix):
|
|
"Returns the migration(s) which match the given app label and name _prefix_"
|
|
# Make sure we have the disk data
|
|
if self.disk_migrations is None:
|
|
self.load_disk()
|
|
# Do the search
|
|
results = []
|
|
for l, n in self.disk_migrations:
|
|
if l == app_label and n.startswith(name_prefix):
|
|
results.append((l, n))
|
|
if len(results) > 1:
|
|
raise AmbiguityError("There is more than one migration for '%s' with the prefix '%s'" % (app_label, name_prefix))
|
|
elif len(results) == 0:
|
|
raise KeyError("There no migrations for '%s' with the prefix '%s'" % (app_label, name_prefix))
|
|
else:
|
|
return self.disk_migrations[results[0]]
|
|
|
|
@cached_property
|
|
def graph(self):
|
|
"""
|
|
Builds a migration dependency graph using both the disk and database.
|
|
"""
|
|
# Make sure we have the disk data
|
|
if self.disk_migrations is None:
|
|
self.load_disk()
|
|
# And the database data
|
|
if self.applied_migrations is None:
|
|
recorder = MigrationRecorder(self.connection)
|
|
self.applied_migrations = recorder.applied_migrations()
|
|
# Do a first pass to separate out replacing and non-replacing migrations
|
|
normal = {}
|
|
replacing = {}
|
|
for key, migration in self.disk_migrations.items():
|
|
if migration.replaces:
|
|
replacing[key] = migration
|
|
else:
|
|
normal[key] = migration
|
|
# Calculate reverse dependencies - i.e., for each migration, what depends on it?
|
|
# This is just for dependency re-pointing when applying replacements,
|
|
# so we ignore run_before here.
|
|
reverse_dependencies = {}
|
|
for key, migration in normal.items():
|
|
for parent in migration.dependencies:
|
|
reverse_dependencies.setdefault(parent, set()).add(key)
|
|
# Carry out replacements if we can - that is, if all replaced migrations
|
|
# are either unapplied or missing.
|
|
for key, migration in replacing.items():
|
|
# Do the check
|
|
can_replace = True
|
|
for target in migration.replaces:
|
|
if target in self.applied_migrations:
|
|
can_replace = False
|
|
break
|
|
if not can_replace:
|
|
continue
|
|
# Alright, time to replace. Step through the replaced migrations
|
|
# and remove, repointing dependencies if needs be.
|
|
for replaced in migration.replaces:
|
|
if replaced in normal:
|
|
# We don't care if the replaced migration doesn't exist;
|
|
# the usage pattern here is to delete things after a while.
|
|
del normal[replaced]
|
|
for child_key in reverse_dependencies.get(replaced, set()):
|
|
normal[child_key].dependencies.remove(replaced)
|
|
normal[child_key].dependencies.append(key)
|
|
normal[key] = migration
|
|
# Finally, make a graph and load everything into it
|
|
graph = MigrationGraph()
|
|
for key, migration in normal.items():
|
|
graph.add_node(key, migration)
|
|
for key, migration in normal.items():
|
|
for parent in migration.dependencies:
|
|
graph.add_dependency(key, parent)
|
|
return graph
|
|
|
|
|
|
class BadMigrationError(Exception):
|
|
"""
|
|
Raised when there's a bad migration (unreadable/bad format/etc.)
|
|
"""
|
|
pass
|
|
|
|
|
|
class AmbiguityError(Exception):
|
|
"""
|
|
Raised when more than one migration matches a name prefix
|
|
"""
|
|
pass
|