如何更新文档以在 mongoose 中嵌入来自不同集合的现有文档

Question

I have two schemas called Fruit and Person and their collections are fruits and people respectively. They both belong in the db called fruitsDB .

Fruit schema:

const fruitSchema = new mongoose.Schema({
  name: String,
  score: Number,
  review: String
});

const Fruit = mongoose.model('Fruit', fruitSchema);

Person schema:

const personSchema = new mongoose.Schema({
  name: String,
  age: Number,
  favouriteFruit: fruitSchema //creating a relationship with the fruitschema
});

const Person = mongoose.model('Person', personSchema);

I have already inserted some docs in to the fruits collection and this is how it looks like:

{ "_id" : ObjectId("5f0ef3efcb6ec717ecda8049"), "name" : "Apple", "score" : 8, "review" : "Pretty solid as a fruit.", "__v" : 0 }
{ "_id" : ObjectId("5f0efa8ee37b6309d8d968fe"), "name" : "Kiwi", "score" : 10, "review" : "The best fruit!", "__v" : 0 }
{ "_id" : ObjectId("5f0efa8ee37b6309d8d968ff"), "name" : "Orange", "score" : 4, "review" : "Too sour for me!", "__v" : 0 }
{ "_id" : ObjectId("5f0efa8ee37b6309d8d96900"), "name" : "Banana", "score" : 7, "review" : "It's nice", "__v" : 0 }
{ "_id" : ObjectId("5f11bc01574df316f4072a46"), "name" : "Pineapple", "score" : 8, "review" : "Great fruit!", "__v" : 0 }

And this is how the people collection looks like:

{
        "_id" : ObjectId("5f11b3e1be240f0c50ca3b26"),
        "name" : "John",
        "age" : 37,
        "__v" : 0
}
{
        "_id" : ObjectId("5f11b62c2ae86609ece9287f"),
        "name" : "Amy",
        "age" : 12,
        "__v" : 0
}

If "John" had a favourite fruit, I want to embed one 'fruit' doc (for eg: Kiwi) from the 'fruits' collection for the "John" field as the favouriteFruit field. Like this:

{
                 "_id" : ObjectId("5f11b3e1be240f0c50ca3b26"),
                "name" : "John",
                 "age" : 37,
       "favouriteFruit": {
                             "_id" : ObjectId("5f0efa8ee37b6309d8d968fe"),
                            "name" : "Kiwi",
                            "score" : 10,
                           "review" : "The best fruit!",
                            "__v" : 0
                         },
                "__v" : 0
}

How can I do this in mongoose? How can I update the "John" document that way to embed an existing document "Kiwi" from the fruits collection?

Answer 1

I think there is a workaround for this problem. The whole problem can be broken into 2 parts.

1. Retrieving the desired fruit from fruits collection.
2. Updating the desired document with the retrieved fruit document from step one.

Both the step can be performed using Mongoose.

Fruit.findOne({name: "Kiwi"}, function(err, fruit) {
    if(err) {
        console.log("Error finding Fruit.");
    }
    else {
        Person.updateOne({name: "John"}, {favouriteFruit: fruit }, function(err) {
            if (err) {
                console.log(err);
            } else {
                mongoose.connection.close();
                console.log("Successfully updated document.");
            }
        });
    }
});

Answer 2

This is not an answer, but I wanted to sort out a misunderstanding and the comment box is limited.

favouriteFruit: fruitSchema //creating a relationship with the fruitschema

This above is not a relationship, it's a subdocument using the fruitSchema. If you were to add kiwi as a favourite fruit, then it would be a completely different kiwi, only existing as a subdocument in the Person-document. Updates to the kiwi-document in the fruits-collection would not reflect to this kiwi.

While it's probably not what you want right now, it is still very often the most desirable pattern with mongodb, because you don't have to even think when retrieving data. Duplicate data doesn't matter much. MongoDb is non-relational.

But you can still get related documents by using mongoose populate:

// You make the schema like this:

const personSchema = new mongoose.Schema({
  name: String,
  age: Number,
  favFruit: { type: ObjectId, ref: 'Fruit' } // This will store nothing but the object-id
});

You can still save it as you would normally

const kiwi = await Fruit.findOne({ name: "kiwi" }).exec();
const ben = new Person({ name: "Ben", age: 26 });
person.favFruit = kiwi;
await ben.save(); // The schema will filter away everything but the id from favFruit.

But later when you retrieve Ben again, you'll find that his fav fruit is nothing but an ObjectID::

const ben = await Person.findOne({ name: "Ben" }).exec();
console.log( ben.favFruit );   // ObjectID("abc123...")

So now you need to populate the field when you want to use it:

const ben = await Person.findOne({ name: "Ben" }).populate("favFruit").exec();
console.log( ben.favFruit ); // { _id: ObjectID("abc123..."), name: "Kiwi", .... }

Mongoose will make two db-queries to make this work. (It's still very fast, but one should be aware.)

Answer 3

I used {$set: {favouriteFruit: kiwi}} instead of {favouriteFruit: kiwi} to update the document

Person.updateOne({name: 'John'}, {$set : {favouriteFruit: kiwi}}, (err)=>{
    if(err){
        console.log(err);
    }
    else{
        console.log("successfully updated");
    }
});