CODEWITHSUNDEEP
javascriptmongodbreferencemongoose
Wesley
Wesley

Reputation: 117

Removing Mongo document and all of its references?

At a high level, I'm looking to remove a document from Mongo as well as its referenced documents. Take a look at the following example Schemas:

var studentSchema = mongoose.Schema({
  email: String,
  name: String,
  _class: { type: String, ref: 'Class' },
  books: [{ type: Schema.Types.ObjectId, ref: 'Book' }]
});
module.exports = mongoose.model('Student', studentSchema);


var classSchema = mongoose.Schema({
  gradeLevel: Number,
  students: [{ type: Schema.Types.ObjectId, ref: 'Student' }]
});
module.exports = mongoose.model('Class', classSchema);


var bookSchema = mongoose.Schema({
  author: String,
  subject: String,
  pages: Number
});
module.exports = mongoose.model('Book', bookSchema);

Now, my question is two fold:
1. If I want to .remove() a Class document from my database AND all Student documents referenced to it, what is the best way of doing this? //currently looping through students with the given class id and individually removing, then finally removing the class document.
2. If I want to .remove() a Class document from the db AND all Students AND their Books, is there a way to do this simply through a special remove statement in mongo? //Currently finding all students, removing their books, then remove themselves, then remove their referenced class.


Ideally, I would like a statement the can remove a mongo document, and anything referenced to it, along with any sub-references that sub-document may have. (e.g: Remove a Class and have mongo auto-remove all Students and their Books) Is this possible?

Upvotes: 1

Views: 2881

Answers (1)

Reto
Reto

Reputation: 3141

there is no statement that does what you want in mongoDb or mongoose. MongoDB is not the best choice if such operations that span multiple collections are very important for your application ("no automatically supported joins and referential integrity in MongoDB"). You also might need to model your data more "mongo-like" to achieve what you want.

You can do it more efficiently than looping if you have backreferences. The model.find() function returns a query object, that has a .remove(cb) method

mongooose.model('Student').find({_class: myClassToRemove._id}).remove(function(err) {});

For your books this will not work, because Book does not have a reference to Student. But if you do not share books between different students, then you should just store the books within the student object as "embedded documents" instead of using a different model and references. Then they will be deleted automatically when you delete a student.

If you do share one book instance between multiple students, you can not automatically delete the book when you delete a student, because you don't know whether another student uses the same book instance.

Upvotes: 2

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