new_contents: from sqlalchemy_utils import UUIDType
  
  from zou.app import db
  from zou.app.models.serializer import SerializerMixin
  from zou.app.models.base import BaseMixin
  
  
  class AssetInstance(db.Model, BaseMixin, SerializerMixin):
      asset_id = db.Column(UUIDType(binary=False), db.ForeignKey('entity.id'))
      shot_id = db.Column(UUIDType(binary=False), db.ForeignKey('entity.id'))
      number = db.Column(db.Integer())
      description = db.Column(db.String(200))
  
      __table_args__ = (
          db.UniqueConstraint(
              'asset_id',
              'shot_id',
              'number',
              name='asset_instance_uc'
          ),
      )
  
subject: Add Asset Instance model