#32011: Error when calling add() on ManyRelatedManager with intermediary model
-------------------------------------+-------------------------------------
Reporter: Philipp | Owner: nobody
Maino |
Type: Bug | Status: new
Component: | Version: 2.1
Documentation | Keywords: ManyToMany,
Severity: Normal | ManyRelatedManager
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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Django is not managing our databases for us, therefor I created the table
RulesetRuleMap to handle the ManyToMany relationship between Ruleset and
Rule: Each Ruleset can consist of multiple Rules and each Rule can be used
in multiple Rulesets.
**Models**
{{{
class Rule(models.Model):
id = models.BigAutoField(primary_key=True)
percentage_of_total = models.FloatField(blank=False, null=False)
_rule_parameter = models.ForeignKey('RuleParameter',
models.DO_NOTHING, blank=False, null=False)
class Meta:
managed = False
db_table = '_rule'
class Ruleset(models.Model):
id = models.BigAutoField(primary_key=True)
name = models.CharField(max_length=300, blank=False, null=False)
description = models.CharField(max_length=300, blank=False,
null=False)
rules = models.ManyToManyField('Rule', through="RulesetRuleMap")
class Meta:
managed = False
db_table = '_ruleset'
class RulesetRuleMap(models.Model):
id = models.BigAutoField(primary_key=True)
_rule = models.ForeignKey('Rule', models.CASCADE)
_ruleset = models.ForeignKey('Ruleset', models.CASCADE)
class Meta:
managed = False
db_table = '_ruleset_rule_map'
}}}
**Serializers**
{{{
class RulesetRuleMapSerializer(serializers.ModelSerializer):
class Meta:
model = db_models.RulesetRuleMap
fields = '__all__'
class RuleSerializer(serializers.ModelSerializer):
class Meta:
model = db_models.Rule
fields = '__all__'
class RulesetSerializer(serializers.ModelSerializer):
rules = RuleSerializer(many=True)
class Meta:
model = db_models.Ruleset
fields = '__all__'
def create(self, validated_data):
rules_data = validated_data.pop('rules')
ruleset = db_models.Ruleset.objects.create(**validated_data)
rules_storage =[]
for rule_data in rules_data:
rule, created =
db_models.Rule.objects.get_or_create(**rule_data)
rules_storage.append(rule)
ruleset.rules.add(*rules_storage, through_defaults={})
return ruleset
}}}
On a homepage the user can add/modify a Ruleset and add/modify the
assosiated Rules. On submission we receive a payload like this:
{{{
{
"id": None,
"name": "Split_50.0_Param1_50.0_Param2",
"description": "test",
"rules": [
{
"id": None,
"percentage_of_total": "50",
"tc_rule_parameter": "3"
},
{
"id": None,
"percentage_of_total": "50",
"tc_rule_parameter": "2"
}
]
}
}}}
As described in [https://www.django-rest-framework.org/api-guide/relations
/#writable-nested-serializers/ DRF] I defined a custom create() for the
nested RulesetSerializer to handle the creation of multiple objects.
According to [https://docs.djangoproject.com/en/3.1/topics/db/models
/#extra-fields-on-many-to-many-relationships / Django] one should be able
to
----
use add(), create(), or set() to create relationships, as long as you
specify through_defaults for any required fields.
----
When executing ruleset.rules.add(*rules_storage, through_defaults={}) I
get the error
**''{TypeError}add() got an unexpected keyword argument
'through_defaults'''**
When executing ruleset.rules.add(*rules_storage) I get the error
**''{AttributeError}Cannot use add() on a ManyToManyField which specifies
an intermediary model.Use database_models.TcRulesetRuleMap's Manager
instead.''**
Is there a mistake in my model and/or serializer set up or is there a bug
in django?
--
Ticket URL: <https://code.djangoproject.com/ticket/32011>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
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