Querying a MongoDB Collection in Node.js Applications

Review the following code, which demonstrates how to query documents in MongoDB with Node.js.

Using find()

The find() method is a read operation that returns a cursor to the documents that match the query. The find() method takes a query or filter document as an argument. If you do not specify a query document, the find() method returns all documents in the collection.

In this example, we find all accounts that have a balance greater than or equal to 4700. The find() method accepts a query filter, which we assign to a variable called documentsToFind. We process each document that’s returned from the find() method by iterating the cursor, which is assigned to the variable result.

const dbname = "bank"
const collection_name = "accounts"
 
const accountsCollection = client.db(dbname).collection(collection_name)

// Document used as a filter for the find() method
const documentsToFind = { balance: { $gt: 4700 } }
 
const main = async () => {
 try {
   await connectToDatabase()
   // find() method is used here to find documents that match the filter
   let result = accountsCollection.find(documentsToFind)
   let docCount = accountsCollection.countDocuments(documentsToFind)
   await result.forEach((doc) => console.log(doc))
   console.log(`Found ${await docCount} documents`)
 } catch (err) {
   console.error(`Error finding documents: ${err}`)
 } finally {
   await client.close()
 }
}

main()

Using findOne()

In this example, we return a single document from a query, which is assigned to a variable called documentToFind. We use the findOne() method on the collection object to return the first document that matches the filter criteria, which are defined in the documentToFind variable.

const dbname = "bank"
const collection_name = "accounts"
 
const accountsCollection = client.db(dbname).collection(collection_name)

// Document used as a filter for the findOne() method
const documentToFind = { _id: ObjectId("62a3638521a9ad028fdf77a3") }

const main = async () => {
 try {
   await connectToDatabase()
   // findOne() method is used here to find a the first document that matches the filter
   let result = await accountsCollection.findOne(documentToFind)
   console.log(`Found one document`)
   console.log(result)
 } catch (err) {
   console.error(`Error finding document: ${err}`)
 } finally {
   await client.close()
 }
}

main()