CRUD Operations

CRUD stands for Create, Read, Update, Delete. These are the four fundamental operations for working with data in any database. MongoDB provides methods for each one, and they all follow a similar pattern: you call a method on a collection and pass in a document or query.

The examples in this chapter use the Mongo shell (mongosh), but the method names and syntax are the same when using the Node.js driver.

Create

insertOne

insertOne adds a single document to a collection:

db.employees.insertOne({
    name: "Kenji",
    department: "Engineering",
    salary: 72000
})

The result object includes an insertedId field containing the _id that MongoDB assigned to the new document.

insertMany

insertMany adds multiple documents at once. Pass in an array of documents:

db.employees.insertMany([
    { name: "Dana", department: "Marketing", salary: 65000 },
    { name: "Olga", department: "Engineering", salary: 78000 },
    { name: "Carlos", department: "Marketing", salary: 61000 }
])

The result includes an insertedIds object mapping the index of each document to its generated _id.

Read

findOne

findOne returns the first document that matches a query:

db.employees.findOne({ name: "Kenji" })

If no document matches, findOne returns null.

find

find returns all documents that match a query:

db.employees.find({ department: "Engineering" })

With no arguments, find returns every document in the collection:

db.employees.find()

Query Filters

The object you pass to find or findOne is a query filter. It specifies which documents to match. A filter with multiple fields requires all of them to match:

db.employees.find({ department: "Engineering", salary: 72000 })

This returns only documents where the department is "Engineering" and the salary is 72000.

MongoDB also supports comparison operators for more flexible queries. These are covered in the Data Modelling and Queries chapter.

Update

updateOne

updateOne takes two arguments: a filter (which document to find) and an update (what to change):

db.employees.updateOne(
    { name: "Kenji" },
    { $set: { salary: 75000 } }
)

The result includes matchedCount (how many documents matched the filter) and modifiedCount (how many were actually changed).

updateMany

updateMany modifies all documents that match a filter:

db.employees.updateMany(
    { department: "Marketing" },
    { $set: { department: "Growth" } }
)

This renames the department from "Marketing" to "Growth" for every matching employee.

Update Operators

The $set operator replaces the value of a field, or adds the field if it does not exist. MongoDB has several other update operators:

// Give Kenji a raise of 5000
db.employees.updateOne(
    { name: "Kenji" },
    { $inc: { salary: 5000 } }
)

// Add a skill to an employee's skills array
db.employees.updateOne(
    { name: "Olga" },
    { $push: { skills: "Python" } }
)

Delete

deleteOne

deleteOne removes the first document that matches a filter:

db.employees.deleteOne({ name: "Carlos" })

The result includes deletedCount, which tells you how many documents were removed (either 0 or 1).

deleteMany

deleteMany removes all documents that match a filter:

db.employees.deleteMany({ department: "Growth" })

To delete every document in a collection, pass an empty filter:

db.employees.deleteMany({})