如何在 Mongoose.js 中检查前/后更新挂钩中的修改字段

Question

I need to know modified fields or if a specific field was modified in pre or post update hook in a Mongoose schema. I tried the following, but still unable to figure it out:

schema.post('update', function (doc) {
    //check modified fields or if the name field was modified and then update doc
});

I know maybe there is a method isModified like in pre save but I don't know how to do the same with update hooks. Any suggestions will be appreciated.

Answer 1

If you want to know what fields you are modifying, then you need to issue an update command by calling save :

Tank.findById(id, function (err, tank) {
  if (err) return handleError(err);

  tank.set({ size: 'large' });
  tank.save(function (err, updatedTank) {
    if (err) return handleError(err);
    res.send(updatedTank);
  });
});

This way pre-save hook will be invoked and you will be having access to:

Document.prototype.modifiedPaths()

because this in pre-save hook refers to the document:

TankSchema.pre('save', function (next) {
  // ...
  this.modifiedPaths();
  // ...
});

On the other hand, you will not be able to achieve the same result when issuing an update command by calling update :

Tank.update({ _id: id }, { $set: { size: 'large' }}, callback);

because when calling update , document hooks (eg pre-save , post-save ) are not being executed at all. Instead, query hooks are being executed (eg pre-update , post-update ) in that case. And the issue with query hooks is that this inside of them does not reference the document, so this.modifiedPaths === undefined

schema.post('update', function (doc) {
  // `this` refers to model.Query
  // `doc` refers to CommandResult 
});

Answer 2

try it:

 schema.post('update', function () {
     const modifiedFields = this.getUpdate().$set;
     // ...
 });

Answer 3

There is no direct way of doing it. There is a variable called isNew which is being tracked by mongoose to check if a new document is created.

see Document#isNew for information on Document#isNew

However, you can created your own tracker to check in post save hook to identify wether document is updated or not.

schema.pre('save', function (doc) {
    this.isDocUpdated = false;
    if (this.isModified()) {
        this.isDocUpdated = true;
    }
});

schema.post('save', function (doc) {
    if (this.isDocUpdated) {
        console.log('post save hook called');
    }
});

Answer 4

For post()

Schema.post('update', function () {
        const modifiedFields = this.getUpdate().$set;
        console.log(modifiedFields);
});

For pre()

schema.pre('update', function () {
        const modifiedFields = this.getUpdate();
        delete modifiedFields['$set'];
        delete modifiedFields['$setOnInsert'];
        console.log(modifiedFields);
});

Answer 5

Have a look at:

http://mongoosejs.com/docs/api.html#document_Document-modifiedPaths

Returns an array of paths modified.

  schema.pre('save', function (next) {
    //check modified fields or if the name field was modified and then update doc
    var modified_paths = this.modifiedPaths();
    next();
  })