No mixins pattern

gistfile1.js

const createModelHelpers = (model) => {
  const query = (trx) => model.query(trx).withSchema('workout');

  const getById = ({ trx, id }) => query(trx).findById(id);

  const insert = async ({ trx, input }) => query(trx).insert(input).returning('*');

  return {
    query,
    getById,
    insert,
  };
};

const {
  query,
  getById,
  insert,
} = createModelHelpers(TrainerModel);

export const createLoader = ({ knex }) => {
  TrainerModel.knex(knex);

  return {
    // Exposing getById
    getById,

    // Custom insert implementation
    insert: async ({ input }) => {
      // Validate input

      const inserted = await insert({ input });

      return inserted;
    },

    custom: async ({ id }) => {
      // Start a new transaction
      const result = await transaction(TrainerModel, async (TransactionModel, trx) => {
        // Use the bound version of the transaction model directly
        const trainer = await TransactionModel.findById(id);

        // Use the bound version or the transaction in the query helper
        const other = await query(TransactionModel).findById(id);
        const third = await query(trx).findById(id);

        // Update any random table
        const inserted = await trx('random_table').insert({ stuff: trainer.updatedAt });

        return { inserted, other, third };
      });

      // custom return type for some reason
      return {
        ...result,
        custom: 'stuff',
      };
    },
  };
};