The difference between update, updateOne and updateMany functions in Mongoose

• Model.updateMany()

Same as update(), except MongoDB will update all documents that match filter (as opposed to just the first one) regardless of the value of the multi option.

• Model.updateOne()

Same as update(), except it does not support the multi or overwrite options.

Take a look at the source code of these three methods:

update:

Model.update = function update(conditions, doc, options, callback) {
  _checkContext(this, 'update');

  return _update(this, 'update', conditions, doc, options, callback);
};

updateMany:

Model.updateMany = function updateMany(conditions, doc, options, callback) {
  _checkContext(this, 'updateMany');

  return _update(this, 'updateMany', conditions, doc, options, callback);
};

updateOne:

Model.updateOne = function updateOne(conditions, doc, options, callback) {
  _checkContext(this, 'updateOne');

  return _update(this, 'updateOne', conditions, doc, options, callback);
};

They call the _update function with different op parameter finally.

_update:

/*!
 * Common code for `updateOne()`, `updateMany()`, `replaceOne()`, and `update()`
 * because they need to do the same thing
 */

function _update(model, op, conditions, doc, options, callback) {
  const mq = new model.Query({}, {}, model, model.collection);

  callback = model.$handleCallbackError(callback);
  // gh-2406
  // make local deep copy of conditions
  if (conditions instanceof Document) {
    conditions = conditions.toObject();
  } else {
    conditions = utils.clone(conditions);
  }
  options = typeof options === 'function' ? options : utils.clone(options);

  const versionKey = get(model, 'schema.options.versionKey', null);
  _decorateUpdateWithVersionKey(doc, options, versionKey);

  return mq[op](conditions, doc, options, callback);
}

Source code