CODEWITHSUNDEEP
mongoose
falah mahmood
falah mahmood

Reputation: 465

Difference between Document and Query in mongoose?

According to the mongoose documentation:

Mongoose models provide several static helper functions for CRUD operations. Each of these functions returns a mongoose Query object.

Models are fancy constructors compiled from Schema definitions.

Mongoose documents represent a one-to-one mapping to documents as stored in MongoDB. Each document is an instance of its Model.

Now, all the static CRUD functions on the Model return a Query. However, in the documents section, under guides, it says "When you load documents from MongoDB using model functions like findOne(), you get a Mongoose document back.".

At one place Model.findOne() is returning a Query object and at a different section its returning a document...Can someone please help explain this.

Upvotes: 5

Views: 610

Answers (2)

Yusuf Isakov
Yusuf Isakov

Reputation: 21

Yesterday I read @Aya Othman's answer several times and understood it only after reading the Mongoose documents a few times. So I thought maybe noobs like myself need a bit different explanation. As I understood, we know that Mongoose models have several functions for CRUD operations such as Model.find(), Model.findById(), Model.findByIdAndDelete(), etc. For example, when User.findById(userId) function is invoked without keyword await it doesn't fetch the user from the database and return document but it returns a query. This query is an object. It has methods. Now if we want to fetch the user we can call exec() method of the query.

const query = User.findById(userId)

// fetch only user's name and age
query.select("name age")

// execute query at a later time
// `await query.exec()` is equivalent to `await User.findById(userId)`
const user = await query.exec()
console.log(user instanceof mongoose.Document) // true

For further details I recommend reading about Queries and Documents.

Upvotes: 1

Aya Othman
Aya Othman

Reputation: 136

Really a good question. Simply creating a query doesn't mean loading the document from the Model. When you use findOne() method you just create a query, it will return Query Object. When you execute this query to load the document from the model, in this case the return is a document Object. Hope the following example will clarify the idea, knowing that this is not the only way to execute the query.

The first part is to create the query

    const query = myModel.findOne({ name })
    console.log(query.constructor.name) // Query
    console.log(query instanceof mongoose.Query) // True
    console.log(query instanceof mongoose.Document) // False

The second part is to execute it

    query.then((document) => {
        console.log(document.constructor.name) // model
        console.log(document instanceof mongoose.Query) // False
        console.log(document instanceof mongoose.Document) // True
        response.json(document)
    }).catch((error) => {
        response.json(error)
    })

Upvotes: 3

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