Sequelize BelongsToManyAddAssociationMixin performing update instead of insert in polymorphic table

Question

I'm having a problem within my application that is related to multiple tables/models arranged in a Many:Many relationship but also leverages polymorphic columns and is using the BelongsToManyAddAssociationMixin. I am unable to insert multiple records in a M:N relationship because I'm unable to tell Sequelize to change the unique fields to include roleableId

Essentially I have a User model, a Role model, a relationship table called UserRole and other models which are "roleable" (For the sake of this example, one model is a Facility)

So essentially my UserRole model looks like

export class UserRole extends Model {
  public readonly id!: UUID
  public RoleId!: UUID
  public UserId!: UUID
  public roleableType!: string
  public roleableId!: string

  public readonly User!: User
  public readonly Role!: Role

  public getUser!: BelongsToGetAssociationMixin<User>
  public getRole!: BelongsToGetAssociationMixin<Role>
}

export const initializeUserRole = (sequelize: Sequelize) => {
  UserRole.init(
    {
      RoleId: {
        type: DataTypes.UUID,
        allowNull: false,
        validate: {
          isUUID: 4,
        },
        field: 'role_id',
      },
      UserId: {
        type: DataTypes.UUID,
        allowNull: false,
        validate: {
          isUUID: 4,
        },
        field: 'user_id',
      },
      roleableId: {
        type: DataTypes.UUID,
        field: 'roleable_id',
        validate: {
          isUUID: 4,
        },
      },
      roleableType: {
        type: DataTypes.STRING,
        field: 'roleable_type',
      },
    },
    {
      timestamps: false,
      sequelize,
      tableName: TableNames.USER_ROLES,
    }
  )
}

In my scenario, I would have a role named Sales Rep and it's primary key is a UUID

In theory, I would like to create a new record for the user to have the SalesRep role twice in my UserRole table, one with values for roleableId & roleableType and one where those values are null.

Using mixins, I'm able to add these roles with something like

const randomUser = await userFactory()
const salesRepRole = await roleFactory({ roleName: 'Sales Rep' })

await randomUser.addRole(salesRepRole)

^^^ This works properly

But if I try to do something like:

const randomUser = await userFactory()
const randomFacility = await facilityFactory()
const salesRepRole = await roleFactory({ roleName: 'Sales Rep' })

await randomUser.addRole(salesRepRole)
await randomuser.addRole(salesRepRole, { through: { roleableId: randomFacility.id, roleableType: 'facility' }})

What will happen is that instead of performing a new insert into my UserRole table, instead Sequelize will identify that there is already a record based upon User.id & Role.id and will perform an UPDATE instead, resulting in only one record being returned.

I'm not sure how to indicate to Sequelize that instead of putting a unique constraint on User.id & Role.id, I really need it to be User.id, Role.id & roleableId

My work around right now has been to simply just roll my own add<Model> function which will perform an INSERT properly (adding an index on my DB to check for unique instances of user_id,role_id,roleable that throw an error if this combination already exists) but this feels a bit dirty and I'd rather try to utilize the mixin as much as possible, especially if I also have to add a BelongsToManyAddAssociationsMixin version as well for addRoles

Does anyone have any ideas? I'm happy to elaborate more if that helps.

Thanks!