This function lets you save an instance of a model to another database based on a connection argument. Useful when doing data migrations across databases. Connection is anything that would work as a django.db.connection
I'm not sure if this handles proxy models or model inheritance properly, though.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 | def save_using_connection(instance, connection, force_insert=False, force_update=False, raw=False):
model = instance.__class__
cls = instance.__class__
meta = cls._meta
origin = cls
if not meta.proxy:
non_pks = [f for f in meta.local_fields if not f.primary_key]
# First, try an UPDATE. If that doesn't update anything, do an INSERT.
pk_val = instance._get_pk_val(meta)
pk_set = pk_val is not None
record_exists = True
manager = cls._base_manager
if pk_set:
# Determine whether a record with the primary key already exists.
if (force_update or (not force_insert and
manager.filter(pk=pk_val).extra(select={'a': 1}).values('a').order_by())):
# It does already exist, so do an UPDATE.
if force_update or non_pks:
values = [(f, None, (raw and getattr(instance, f.attname) or f.pre_save(instance, False))) for f in non_pks]
q = manager.filter(pk=pk_val)
q.query.connection = connection
rows = q._update(values)
if force_update and not rows:
raise DatabaseError("Forced update did not affect any rows.")
else:
record_exists = False
if not pk_set or not record_exists:
if not pk_set:
if force_update:
raise ValueError("Cannot force an update in save() with no primary key.")
values = [(f, f.get_db_prep_save(raw and getattr(instance, f.attname) or f.pre_save(instance, True))) for f in meta.local_fields if not isinstance(f, AutoField)]
else:
values = [(f, f.get_db_prep_save(raw and getattr(instance, f.attname) or f.pre_save(instance, True))) for f in meta.local_fields]
if meta.order_with_respect_to:
field = meta.order_with_respect_to
values.append((meta.get_field_by_name('_order')[0], manager.filter(**{field.name: getattr(instance, field.attname)}).count()))
record_exists = False
update_pk = bool(meta.has_auto_field and not pk_set)
if values:
# Create a new record.
result = _insert(model, connection, values, return_id=update_pk)
else:
# Create a new record with defaults for everything.
result = _insert(model, connection, [(meta.pk, connection.ops.pk_default_value())], return_id=update_pk, raw_values=True)
if update_pk:
setattr(instance, meta.pk.attname, result)
|
More like this
- Template tag - list punctuation for a list of items by shapiromatron 8 months, 3 weeks ago
- JSONRequestMiddleware adds a .json() method to your HttpRequests by cdcarter 9 months ago
- Serializer factory with Django Rest Framework by julio 1 year, 3 months ago
- Image compression before saving the new model / work with JPG, PNG by Schleidens 1 year, 4 months ago
- Help text hyperlinks by sa2812 1 year, 5 months ago
Comments
Please login first before commenting.