CRUD Operations in Mongo (Shell)

Create, Read, Update, Delete in Mongo (Shell)

Situation: This is a summary of basic Mongo operations in shell. These commands can be used in create, seed test databases outside of the production database.

Basic commands

# show available databases
show dbs

# use a database
use db_name

# show collections within database
show collections

Delete an entire collection

db.collectionName.drop()

Insert one document into a collection

Create a collection and insert one document. Copy a document (i.e., an object or python dictionary) and paste in argument of .insertOne(). What’s inserted is a single object.

db.newCollectionName.insertOne({})

note: MongoServerError: _id fields may not contain '$'-prefixed fields: $oid is not valid for storage. Because mongo shell automatically inserted ids:

Example of two ObjectIds being inserted:

{
  acknowledged: true,
  insertedIds: {
    '0': ObjectId("618d1fb2f5975b1a2ed10b91"),
    '1': ObjectId("618d1fb2f5975b1a2ed10b92")
  }
}

Insert many documents into a collection

note: to avoid MongoServerError with '$'oid is not valid for storage error, edit in VSCode before pasting in mongo shell.

Note, parameter is an array of objects.

db.newCollectionName.insertMany([{}, {}])

Count document(s) inside a collection

db.collection.countDocuments()

Find document where integer value > 9000

Using $gt (greater than) as an example from the Bounty Board project.

Alternatives:

• $lt less than
• $gte greater than or equal to

db.bounties2.find({"reward.amount": {$gt: 9000} }).pretty()

Update one document

Updating season from 1 to 2:

db.bounties2.updateOne({_id: ObjectId("618d2585f5975b1a2ed10b93")}, {$set: {season: 2}})

ReplaceOne instead update

Note: This is more tedious than updating just one field; with replaceOne() you have to update all fields otherwise, they get deleted. Arguably, this makes it more explicit (and safe) way to update.

This replaces key-value pairs in the document with a specific _id to only have 2 key-value pairs (erasing all others).

db.bounties2.replaceOne({_id: ObjectId("618d1cddf5975b1a2ed10b8f")}, {season: 2, "title": "Implement Changes"})

Print more than just 20 documents

bountyboard> db.bounties2.find().forEach((bounties2Data) => {printjson(bounties2Data)})

Return only one field in a document

Here we’re returning “title”, then “reward.amount”.

# return title
db.bounties2.find({}, {title: 1, _id: 0}).pretty()

# return reward.amount
db.bounties2.find({}, {"reward.amount": 1, _id: 0}).pretty()

Joining two collections

Note: Join two collections by customerId

db.bounties2.aggregate([{ $lookup: { from: "customers", localField: "customerId", foreignField: "customerId", as: "customerId" } }])

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