1from plain import models
2from plain.models.db import DatabaseError
3from plain.packages.registry import Packages
4from plain.utils.functional import classproperty
5from plain.utils.timezone import now
6
7from .exceptions import MigrationSchemaMissing
8
9
10class MigrationRecorder:
11 """
12 Deal with storing migration records in the database.
13
14 Because this table is actually itself used for dealing with model
15 creation, it's the one thing we can't do normally via migrations.
16 We manually handle table creation/schema updating (using schema backend)
17 and then have a floating model to do queries with.
18
19 If a migration is unapplied its row is removed from the table. Having
20 a row in the table always means a migration is applied.
21 """
22
23 _migration_class = None
24
25 @classproperty
26 def Migration(cls):
27 """
28 Lazy load to avoid PackageRegistryNotReady if installed packages import
29 MigrationRecorder.
30 """
31 if cls._migration_class is None:
32
33 class Migration(models.Model):
34 app = models.CharField(max_length=255)
35 name = models.CharField(max_length=255)
36 applied = models.DateTimeField(default=now)
37
38 class Meta:
39 packages = Packages()
40 package_label = "migrations"
41 db_table = "plainmigrations"
42
43 def __str__(self):
44 return f"Migration {self.name} for {self.app}"
45
46 cls._migration_class = Migration
47 return cls._migration_class
48
49 def __init__(self, connection):
50 self.connection = connection
51
52 @property
53 def migration_qs(self):
54 return self.Migration.objects.using(self.connection.alias)
55
56 def has_table(self):
57 """Return True if the plainmigrations table exists."""
58 with self.connection.cursor() as cursor:
59 tables = self.connection.introspection.table_names(cursor)
60 return self.Migration._meta.db_table in tables
61
62 def ensure_schema(self):
63 """Ensure the table exists and has the correct schema."""
64 # If the table's there, that's fine - we've never changed its schema
65 # in the codebase.
66 if self.has_table():
67 return
68 # Make the table
69 try:
70 with self.connection.schema_editor() as editor:
71 editor.create_model(self.Migration)
72 except DatabaseError as exc:
73 raise MigrationSchemaMissing(
74 "Unable to create the plainmigrations table (%s)" % exc
75 )
76
77 def applied_migrations(self):
78 """
79 Return a dict mapping (package_name, migration_name) to Migration instances
80 for all applied migrations.
81 """
82 if self.has_table():
83 return {
84 (migration.app, migration.name): migration
85 for migration in self.migration_qs
86 }
87 else:
88 # If the plainmigrations table doesn't exist, then no migrations
89 # are applied.
90 return {}
91
92 def record_applied(self, app, name):
93 """Record that a migration was applied."""
94 self.ensure_schema()
95 self.migration_qs.create(app=app, name=name)
96
97 def record_unapplied(self, app, name):
98 """Record that a migration was unapplied."""
99 self.ensure_schema()
100 self.migration_qs.filter(app=app, name=name).delete()
101
102 def flush(self):
103 """Delete all migration records. Useful for testing migrations."""
104 self.migration_qs.all().delete()