118👍
Update Django 4.0
Django 4.0 documentation recommends using UniqueConstraint with the constraints option instead of unique_together.
Use UniqueConstraint with the constraints option instead.
UniqueConstraint provides more functionality than unique_together. unique_together may be deprecated in the future.
class Hop(models.Model):
migration = models.ForeignKey('Migration')
host = models.ForeignKey(User, related_name='host_set')
class Meta:
constraints = [
models.UniqueConstraint(
fields=['migration', 'host'], name='unique_migration_host_combination'
)
]
Original Answer
I would implement this slightly differently.
I would use a default primary key (auto field), and use the meta class property, unique_together
class Hop(models.Model):
migration = models.ForeignKey('Migration')
host = models.ForeignKey(User, related_name='host_set')
class Meta:
unique_together = (("migration", "host"),)
It would act as a "surrogate" primary key column.
If you really want to create a multi-column primary key, look into this app
28👍
Currently, Django models only support a single-column primary key. If you don’t specify primary_key = True
for the field in your model, Django will automatically create a column id
as a primary key.
The attribute unique_together
in class Meta
is only a constraint for your data.
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5👍
If you should use Django on a legacy database, you can’t modify db_schema.
There is a workaround (ugly) method to fix this issue:
Override the models save or delete function:
# Use a raw SQL statement to save or delete the object
class BaseModel(models.Model):
def get_max_length_unique_key(self):
max_len_unique_key = []
for unique_key in self._meta.unique_together:
if len(unique_key) > len(max_len_unique_key):
max_len_unique_key = unique_key
return max_len_unique_key
def get_db_conn(self):
db_cnn = DbManage(db_ip, db_port, DATABASES_USER, DATABASES_PASSWORD, self._meta.db_table)
db_cnn.connect()
return db_cnn
def save(self, *args, **kwargs):
self.delete()
cnn, databasename = self.get_db_conn()
update_tables = self._meta.db_table
key_list = ""
values_list = ""
for field in self._meta.fields:
key_list += "%s," % field.name
values_list += "\'%s\'," % str(getattr(self, field.name))
key_list = key_list[:len(key_list) - 1]
values_list = values_list[:len(values_list) - 1]
sql = "insert into %s(%s) values(%s)" % (update_tables, key_list, values_list)
logger.info("insert new record to %s" % databasename)
cnn.excute_sql(sql)
cnn.close()
def delete(self, *args, **kwargs):
cnn = self.get_db_conn()
update_tables = self._meta.db_table
sql = "delete from %s where " % update_tables
for uk in self.get_max_length_unique_key():
sql += "%s=\'%s\' and " % (uk, getattr(self, uk))
sql = sql[:len(sql) - 4]
logger.info("delete record from %s" % update_tables)
cnn.excute_sql(sql)
cnn.close()
pass
class Meta:
abstract = True
class ImageList(BaseModel):
field1 = models.CharField(primary_key=True, max_length=30)
field2 = models.CharField(primary_key=True, max_length=30)
field3 = models.CharField(primary_key=True, max_length=30)
body = models.CharField(max_length=2000, blank=True, null=True)
updated_on = models.DateTimeField(blank=True, null=True)
class Meta:
managed = True
db_table = 'image_list'
unique_together = (('field1', 'field2', 'field3'),)
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3👍
Since the latest version of Django (4.0.4 at this time) suggests that the unique_together may be deprecated in the future, a more up-to-date solution would be to use the constraints
option of the Meta class together with the UniqueConstraint
class:
class Hop(models.Model):
migration = models.ForeignKey('Migration')
host = models.ForeignKey(User, related_name='host_set')
class Meta:
constraints = [
UniqueConstraint(fields=['migration', 'host'], name='unique_host_migration'),
]
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