Last active
August 29, 2015 14:24
-
-
Save paridin/4b3e13fb1d4a07b1ba1b to your computer and use it in GitHub Desktop.
Compare objects list and get a list of object to inserted or updated
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
""" | |
Problem You have an input json with which you will create a list of objects, you have to validate that the object will be created if it not exists, if exists determine whether to upgrade or discard depending of they have not undergone any changes. | |
Solution 1) With the input json will be created the list of objects of the class that we insert or updatee | |
2) Read all fields in the database, using one of the fields as key to creating a dictionary with the objects in the database | |
3) Compare the objects and determine if it will be updated, inserted or discarded | |
Django problem: by default only compares the level objects using the primary key (id). Compare field by field is the solution to determine if the object has changed. hints: The _state field is present in every object, and it will produce a random memory location, You can find cache fields so you need to remove these begins with underscore _. The fields excluded can be fk, and these fields produce field_id, so you will needs to exclude it | |
class Country(models.Model): # country code 'MX' -> Mexico | |
code = models.CharField(max_length=2) | |
name = models.CharField(max_length=15) | |
class Client(models.Model): # id=1, name=pedro, country.code=MX, rfc=12345 | |
name = models.CharField(max_length=100) | |
country = models.ForeignKey(Country) | |
rfc = models.CharField(max_length=13) | |
Country.objects.create(**{'code': 'MX', 'name': 'Mexico'}) # creating the country | |
Client(**{'id':1, 'name':'pedro', 'country': country, 'rfc':12345}) # creating the client | |
obj_db = Client.objects.get(id=1) | |
country = Country.objects.get(code='MX') | |
obj_no_db = Client(**{'id':1, 'name':'pedro', 'country': country, 'rfc':12345}) | |
obj_db == obj_no_db # True | |
obj_no_db = Client(**{'id':1, 'name':'pedro', 'country': country, 'rfc':1}) | |
obj_db == obj_no_db # True # but isn't True because the rfc has change, how can compare field by field | |
obj_db.rfc == obj_no_db.rfc # False, I was expected this result when compare obj_db == obj_no_db because they are not equal | |
Solution to compare field by field | |
_obj_1 = [(k,v) for k,v in obj_db.__dict__.items() if k != '_state'] | |
_obj_2 = [(k,v) for k,v in obj_no_db.__dict__.items() if k != '_state'] | |
_obj_1 == _obj_2 # False | |
This is only for one object, and you can include in __eq__ method in your model, but what happen if you need compare a list of object to bulk for insert or update with django-bulk-update. | |
Well my snipped pretends solve that. so | |
How can use it. | |
obj_list = [<Object Client>, <Object Client>, <Object Client>, <Object Client>] | |
get_insert_update(Client, 'id', obj_list) | |
exclude_fields = ['country'] | |
get_insert_update(Client, 'id', obj_list, exclude_fields=exclude_fields) | |
""" | |
import re | |
def get_insert_update(obj, key, obj_list, exclude_fields=None): | |
""" | |
:param obj: The object for compare | |
:param key: a the key for compare to determine if we need to update or insert | |
:param obj_list: list objects to compare | |
:return: to_insert, _update | |
""" | |
db = {} | |
to_insert = [] | |
to_update = [] | |
if key == 'pk': # the field pk doesn't exists so we change to id, because its the same | |
key = 'id' | |
if key in exclude_fields: | |
raise Exception('The key "{}" should not be included in exclude_fields -> {}'.format(key, exclude_fields)) | |
exclude_fields = exclude_fields or [] | |
if 'pk' in exclude_fields: | |
exclude_fields[exclude_fields.index('pk')] = 'id' # we change the field pk, because it doesn't exists | |
exclude_fields_ids = ["{}_id".format(i) for i in exclude_fields] | |
# dumping a db into memory | |
for _obj in obj.objects.all(): | |
if isinstance(key, list): # first check if is a list to create a custom key | |
_key = _get_key(_obj, key) | |
else: | |
_key = _obj.__dict__[key] | |
db[_key] = _obj | |
# read local objects to determine if the record will be insert or update | |
for _obj in obj_list: | |
if isinstance(key, list): # first check if is a list to create a custom key | |
_key = _get_key(_obj, key) | |
else: | |
_key = _obj.__dict__[key] | |
if _key in db: # if the key is in db so we check if it esq | |
obj_db = [(k, v) for k, v in db[_key].__dict__.items() if not re.match('^_.*', k) # excluding _state | |
and k not in exclude_fields_ids | |
and k not in exclude_fields] # excluding field and fields_id | |
obj_tmp = [(k, v) for k, v in _obj.__dict__.items() if not re.match('^_.*', k) # not _state, _cache fields | |
and k not in exclude_fields_ids | |
and k not in exclude_fields] | |
if obj_db != obj_tmp: | |
to_update.append(_obj) # if the object has changed, we update it | |
else: | |
pass # if the object is equal, we didn't do it anything | |
else: | |
to_insert.append(_obj) # because we didn't found into the database, we create it | |
return to_insert, to_update | |
def _get_key(obj, lst): | |
""" | |
create a string key using multiples keys | |
Example: obj.id -> 1, obj.name -> 'foo' | |
lst['id', 'name'] | |
:param lst: list of keys | |
:return: 1_foo | |
""" | |
k = [] | |
for t in lst: | |
k.append(str(obj.__dict__[t])) | |
return "_".split(k) |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment