db_manager many-to-many error

from peewee import *

if __name__ == '__main__':

    # DATABASE SETUP
    database = SqliteDatabase('test_db.db')

    class BaseModel(Model):
        class Meta:
            database = database


    class Block(BaseModel):
        text = TextField(null=True)


    class SelectorID(BaseModel):
        name = CharField(unique=True)

    class SelectorName(BaseModel):
        name = CharField(unique=True)

    class Selector(BaseModel):
        block = ForeignKeyField(Block, backref='selectors')
        selector_id = ForeignKeyField(SelectorID, backref='selectors')
        name = ForeignKeyField(SelectorName, backref='selectors')

    class SelecClass(BaseModel):
        selectors = ManyToManyField(Selector, backref='selector_classes')
        name = CharField(unique=True)

    def create_tables():
        database.connect()
        with database:
            database.create_tables([Block,
                SelectorID, SelectorName, Selector,
                SelecClass,
                SelecClass.selectors.get_through_model()])
        database.close()

    create_tables()


    # DATA
    block = {'text': 'test'}
    selectors = [
        {
            "classes": [
                "wrapper"
            ],
            "id": "",
            "name": "div"
        },
        {
            "classes": [
                "row"
            ],
            "id": "",
            "name": "div"
        },
        {
            "classes": [
                "row" # When I try to insert this selector's class_obj, a duplicate, I get an IntegrityError
            ],
            "id": "",
            "name": "div"
        },
    ]


    # DATA INSERT
    block_object = Block.create(text=block['text'])

    selectors_and_classes = []

    with database.atomic():

        for selector in selectors:

            selector_id, _ = SelectorID.get_or_create(name=selector['id'])
            selector_name, _ = SelectorName.get_or_create(name=selector['name'])

            selector_obj = Selector.create(
                block=block_object,
                selector_id=selector_id,
                name=selector_name,
                )

            s2bc_class_objs = []

            for s2bc_class in selector['classes']:
                selector_class_obj, _ = SelecClass.get_or_create(name=s2bc_class)

                s2bc_class_objs.append(selector_class_obj)

            selectors_and_classes.append((selector_obj, s2bc_class_objs))


    with database.atomic():

        for selector_and_classes in selectors_and_classes:

            selector = selector_and_classes[0]
            selector_class_objs = selector_and_classes[1]

            Selector = Selector.get(selector_obj)

            for class_obj in selector_class_objs:
                Selector.selector_classes.add(class_obj)


# Traceback (most recent call last):
#   File "C:\h\envs\mlpc\lib\site-packages\peewee.py", line 2936, in execute_sql
#     cursor.execute(sql, params or ())
# sqlite3.IntegrityError: UNIQUE constraint failed: selecclass_selector_through.selecclass_id, selecclass_selector_through.selector_id

# During handling of the above exception, another exception occurred:

# Traceback (most recent call last):
#   File "test.py", line 108, in <module>
#     Selector.selector_classes.add(class_obj)
#   File "C:\h\envs\mlpc\lib\site-packages\peewee.py", line 6810, in add
#     accessor.through_model.insert_many(inserts).execute()
#   File "C:\h\envs\mlpc\lib\site-packages\peewee.py", line 1778, in inner
#     return method(self, database, *args, **kwargs)
#   File "C:\h\envs\mlpc\lib\site-packages\peewee.py", line 1849, in execute
#     return self._execute(database)
#   File "C:\h\envs\mlpc\lib\site-packages\peewee.py", line 2567, in _execute
#     return super(Insert, self)._execute(database)
#   File "C:\h\envs\mlpc\lib\site-packages\peewee.py", line 2316, in _execute
#     cursor = database.execute(self)
#   File "C:\h\envs\mlpc\lib\site-packages\peewee.py", line 2949, in execute
#     return self.execute_sql(sql, params, commit=commit)
#   File "C:\h\envs\mlpc\lib\site-packages\peewee.py", line 2943, in execute_sql
#     self.commit()
#   File "C:\h\envs\mlpc\lib\site-packages\peewee.py", line 2725, in __exit__
#     reraise(new_type, new_type(*exc_args), traceback)
#   File "C:\h\envs\mlpc\lib\site-packages\peewee.py", line 183, in reraise
#     raise value.with_traceback(tb)
#   File "C:\h\envs\mlpc\lib\site-packages\peewee.py", line 2936, in execute_sql
#     cursor.execute(sql, params or ())
# peewee.IntegrityError: UNIQUE constraint failed: selecclass_selector_through.selecclass_id, selecclass_selector_through.selector_id