orm['model'].objects.create(attr=some_value) 导致 IntegrityError

Question

我的模型 Backlog 和实体之间存在一对一的正向关系。每个积压工作都有一个实体。 如果积压缺少一个实体（它在数据库中不存在），我的代码会尝试创建一个实体，并将其链接到缺少实体的积压。

            new_entity = orm['entities.entity'].objects.create(long_name=entity_name)
            if entity_short_name is not None and entity_short_name != '':
                new_entity.name = entity_short_name
            if entity_url is not None:
                new_entity.primary_url = entity_url
            new_entity.save()
            backlog.entity = new_entity
            backlog.save()

每个实体对象都有一个唯一的 ID，称为 guid。 这是我在上面的代码中遇到的错误：

django.db.utils.IntegrityError: duplicate key value violates unique constraint "entities_entity_guid_uniq"
DETAIL:  Key (guid)=(2f49223d-8732-4582-b8a1-7015f515134a) already exists.

实体模型只有一个唯一键：

guid = models.CharField('A globally unique identifier', default = lambda: str(uuid.uuid4()), unique = True, db_index = True)

什么可能导致此完整性错误？检查数据库中是否存在具有此 guid 的实体返回无

**orm 是标准的 django orm 从数据库中获取对象

  File "./manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 399, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 392, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/base.py", line 242, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/base.py", line 285, in execute
    output = self.handle(*args, **options)
  File "/usr/local/lib/python2.7/dist-packages/south/management/commands/migrate.py", line 111, in handle
    ignore_ghosts = ignore_ghosts,
  File "/usr/local/lib/python2.7/dist-packages/south/migration/__init__.py", line 220, in migrate_app
    success = migrator.migrate_many(target, workplan, database)
  File "/usr/local/lib/python2.7/dist-packages/south/migration/migrators.py", line 254, in migrate_many
    result = migrator.__class__.migrate_many(migrator, target, migrations, database)
  File "/usr/local/lib/python2.7/dist-packages/south/migration/migrators.py", line 329, in migrate_many
    result = self.migrate(migration, database)
  File "/usr/local/lib/python2.7/dist-packages/south/migration/migrators.py", line 133, in migrate
    result = self.run(migration, database)
  File "/usr/local/lib/python2.7/dist-packages/south/migration/migrators.py", line 114, in run
    return self.run_migration(migration, database)
  File "/usr/local/lib/python2.7/dist-packages/south/migration/migrators.py", line 84, in run_migration
    migration_function()
  File "/usr/local/lib/python2.7/dist-packages/south/migration/migrators.py", line 60, in <lambda>
    return (lambda: direction(orm))
  File "/usr/local/PATH/0123__.py", line 69, in forwards
    new_entity = orm['entities.entity'].objects.create(long_name=entity_name)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/manager.py", line 157, in create
    return self.get_queryset().create(**kwargs)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/query.py", line 322, in create
    obj.save(force_insert=True, using=self.db)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py", line 545, in save
    force_update=force_update, update_fields=update_fields)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py", line 573, in save_base
    updated = self._save_table(raw, cls, force_insert, force_update, using, update_fields)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py", line 654, in _save_table
    result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py", line 687, in _do_insert
    using=using, raw=raw)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/manager.py", line 232, in _insert
    return insert_query(self.model, objs, fields, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/query.py", line 1514, in insert_query
    return query.get_compiler(using=using).execute_sql(return_id)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/sql/compiler.py", line 903, in execute_sql
    cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/util.py", line 69, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/util.py", line 53, in execute
    return self.cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/utils.py", line 99, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/util.py", line 53, in execute
    return self.cursor.execute(sql, params)
django.db.utils.IntegrityError: duplicate key value violates unique constraint "entities_entity_guid_uniq"
DETAIL:  Key (guid)=(2f49223d-8732-4582-b8a1-7015f515134a) already exists.

Answer 1

guid 字段的问题在于，您将可调用的 uuid.uuid4() 的结果设置为默认值，而不是仅设置每次创建新对象时都会调用的可调用对象，以修复：

def get_unique_id():
    return str(uuid.uuid4())

guid = models.CharField('A globally unique identifier', default=get_unique_id, unique=True, db_index=True)

不要忘记在此更改后运行 makemigrations 和 migrate。