Method increment

src/model.js:3452–3533

* Increment the value of one or more columns. This is done in the database, which means it does not use the values currently stored on the Instance. The increment is done using a * ``` SET column = column + X WHERE foo = 'bar' ``` query. To get the correct value after an increment into the Instan

(fields, options)

   * @returns {Promise<Model[],?number>} returns an array of affected rows and affected count with `options.returning` true, whenever supported by dialect
   */
  static async increment(fields, options) {
    options = options || {};
    if (typeof fields === 'string') fields = [fields];
    if (Array.isArray(fields)) {
      fields = fields.map(f => {
        if (this.rawAttributes[f] && this.rawAttributes[f].field && this.rawAttributes[f].field !== f) {
          return this.rawAttributes[f].field;
        }
        return f;
      });
    } else if (fields && typeof fields === 'object') {
      fields = Object.keys(fields).reduce((rawFields, f) => {
        if (this.rawAttributes[f] && this.rawAttributes[f].field && this.rawAttributes[f].field !== f) {
          rawFields[this.rawAttributes[f].field] = fields[f];
        } else {
          rawFields[f] = fields[f];
        }
        return rawFields;
      }, {});
    }

    this._injectScope(options);
    this._optionsMustContainWhere(options);

    options = Utils.defaults({}, options, {
      by: 1,
      where: {},
      increment: true
    });
    const isSubtraction = !options.increment;

    Utils.mapOptionFieldNames(options, this);

    const where = { ...options.where };

    // A plain object whose keys are the fields to be incremented and whose values are
    // the amounts to be incremented by.
    let incrementAmountsByField = {};
    if (Array.isArray(fields)) {
      incrementAmountsByField = {};
      for (const field of fields) {
        incrementAmountsByField[field] = options.by;
      }
    } else {
      // If the `fields` argument is not an array, then we assume it already has the
      // form necessary to be placed directly in the `incrementAmountsByField` variable.
      incrementAmountsByField = fields;
    }

    // If optimistic locking is enabled, we can take advantage that this is an
    // increment/decrement operation and send it here as well. We put `-1` for
    // decrementing because it will be subtracted, getting `-(-1)` which is `+1`
    if (this._versionAttribute) {
      incrementAmountsByField[this._versionAttribute] = isSubtraction ? -1 : 1;
    }

    const extraAttributesToBeUpdated = {};