id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
32011	Error when calling add() on ManyRelatedManager with intermediary model	Philipp Maino	nobody	"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?"	Bug	closed	Documentation	2.1	Normal	invalid	ManyToMany, ManyRelatedManager		Unreviewed	0	0	0	0	0	0