Objection.js: In the many to many relation $beforeInsert in the join table doesn't call when the relation is polymorphic

[rosendi]

I have a polymorphic many to many relation. The polymorphic join table has a $beforeInsert hook:

class Membership extends Model {
  static tableName = 'memberships';

  async $beforeInsert(ctx) {
    await super.$beforeInsert(ctx);

    const now = moment().utc().format();

    this.createdAt = now;
    this.updatedAt = now;
  }
}

class User extends Model {
  static tableName = 'users';

  static className = 'User';

  static get relationMappings() {
    const Organization = require('./Organization').default; // eslint-disable-line global-require
    const Membership = require('./Membership').default; // eslint-disable-line global-require

    return {
      organizations: {
        relation: BaseModel.ManyToManyRelation,
        modelClass: Organization,

        filter: {
          memberType: User.className,
          objectType: Organization.className,
        },

        join: {
          from: `${User.tableName}.id`,
          to: `${Organization.tableName}.id`,

          through: {
            from: `${Membership.tableName}.memberId`,
            to: `${Membership.tableName}.objectId`,

            beforeInsert(model) {
              model.memberType = User.className;
              model.objectType = Organization.className;
            },
          },
        },
      },
    };
  }
}

When I'm trying create a new organization for the user it fails because the Membership's $beforeInsert wasn't called:

user.$relatedQuery('organizations').insert({ name: 'My Org' })

insert into "memberships" ("memberId", "memberType", "objectId", "objectType") values (?, ?, ?, ?) returning "objectId" undefined
error: null value in column "createdAt" violates not-null constraint

[koskimas]

You need to specify the join table model in the relationMapping:

          through: {
            modelClass: Membership,
            from: `${Membership.tableName}.memberId`,
            to: `${Membership.tableName}.objectId`,

            beforeInsert(model) {
              model.memberType = User.className;
              model.objectType = Organization.className;
            },
          }

[rosendi]

@koskimas ahh! thank you!