Do any task using all the items in a Sequlize model. Just write the task alone. ItemMaper will take care about batch execution and limit

sequelize-forEach-batch.js

class ItemMaper{
  constructor( { model, batchSize, limit }, sequelizeOpts ){
    this.model = model;
    this.batchSize = batchSize || 10;
    this.limit = limit || Infinity;
    this.sequelizeOpts = sequelizeOpts || {};
  }

  async forEachBatch( fn ){
    let offset = -this.batchSize,
      items;
    do{
      offset += this.batchSize;
      items = await this.model.findAll( Object.assign({ offset, limit: this.batchSize }, this.sequelizeOpts ) );
      await fn( items );
    } while( ( items.length === this.batchSize ) && ( offset < this.limit-this.batchSize ) );
    return offset + items.length;
  }

  forEachItem( fn, opts ){
    return this.forEachBatch( items => Promise.map(items, fn, opts ) );
  }
}