mysql - Django的inspectdb不做ManyToManyField

Question

所以我只是测试了一件事，制作了下表。

# Dump of table driverclass
# ------------------------------------------------------------

CREATE TABLE `driverclass` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(20) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

# Dump of table event
# ------------------------------------------------------------

CREATE TABLE `event` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(20) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

# Dump of table driver
# ------------------------------------------------------------

CREATE TABLE `driver` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(20) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

# Dump of table driver_driverclass_event
# ------------------------------------------------------------

CREATE TABLE `driver_driverclass_event` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `driver_id` int(11) unsigned DEFAULT NULL,
  `event_class_id` int(11) unsigned DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `driver_id` (`driver_id`),
  KEY `event_class_id` (`event_class_id`),
  CONSTRAINT `driver_driverclass_event_ibfk_2` FOREIGN KEY (`event_class_id`) REFERENCES `driverclass_event` (`id`),
  CONSTRAINT `driver_driverclass_event_ibfk_1` FOREIGN KEY (`driver_id`) REFERENCES `driver` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

# Dump of table driverclass_event
# ------------------------------------------------------------

CREATE TABLE `driverclass_event` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `event_id` int(11) unsigned DEFAULT NULL,
  `driverclass_id` int(11) unsigned DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `event_id` (`event_id`),
  KEY `driverclass_id` (`driverclass_id`),
  CONSTRAINT `driverclass_event_ibfk_2` FOREIGN KEY (`driverclass_id`) REFERENCES `driverclass` (`id`),
  CONSTRAINT `driverclass_event_ibfk_1` FOREIGN KEY (`event_id`) REFERENCES `event` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

这应该是ManyToManyField方面的关系。然而，Djangos inspectdb 将其视为具有大量外键的 5 个模型。 Djangos inspectdb 没有考虑ManyToManyFields，还是我的数据库模型错误？

Answer 1

您的数据库架构似乎没问题。然而，正如您所发现的，Django 不会自动创建多对多字段。 driverclass_event 和 ** driver_driverclass_event** 的模型是所谓的“直通”模型。通常，您还可以在关系的两端定义 ManyToManyField 并指定正确的“通过”模型:

class Event(db.Model):
    pass

class DriverClass(db.Model):
    events = db.ManyToManyField(Event, through='DriverClassEvent')

class DriverClassEvent(db.Model):
    driver_class = db.ForeignKeyField(DriverClass)
    event = db.ForeignKeyField(Event)

另请参阅:https://docs.djangoproject.com/en/dev/topics/db/models/#extra-fields-on-many-to-many-relationships

通常，当您想要存储有关关系的信息(例如关系的开始日期)或使用外键引用此关系时，通常会使用直通模型。在您的示例中，您存储哪些驱动程序与DriverClassEvent有关系。因此 DriverClassEvent 应该有一个能够引用它的模型。

class DriverDriverClassEvent(db.Model):
    driver = db.ForeignKeyField(Driver)
    driver_class_event = db.ForeignKeyField(DriverClassEvent)

class Driver(db.Model):
    driver_class_events = db.ManyToManyField(DriverClassEvent, through='DriverDriverClassEvent')

现在您可以删除 DriverDriverClassEvent，因为您不存储有关该关系的任何数据，或者引用其他模型中的关系。所以最后一个例子就变成*:

class Driver(db.Model):
    driver_class_events = db.ManyToManyField(DriverClassEvent, db_table='driver_driverclass_event')

* 请注意，您无法控制字段名称，因此这些名称必须与 Django 自动生成的字段名称相匹配。