MongoDB Query Language

MongoDB Query Language is used for CRUD operations to a MongoDB Database. CRUD stands for Create, Read, Update, Delete.

Query Language works with both MongoDB Compass and MongoDB Shell.

Prerequisites: JSON format knowledge, installed MongoDB Compass and Shell.

Let us consider this JSON string. This is a sample document in one collection about movie. You can see the value type of one field is flexible. An array does not have to contain elements in the same type. A document can contain nested documents.

To use the below methods, you first need to

1. Open MongoDB Shell
2. Connect to your cluster, for my example, input mongo "mongodb+srv://learningcluster-mntmv.mongodb.net/test" --username [myUserName]
3. Show databases inside this cluster by inputting show dbs
4. Use one database by typing use [databaseName]
5. Show collections inside this database by typing show collections

From now, the command shall follow this structure:

db.[collectionName].[methodName](param 1, param 2, ...).

where params are defined by particular method signatures.

1) InsertOne

In MongoDB Shell, after connecting to a collection, you can insert one document by typing this command:

db.[collectionName].insertOne({JSON param 1})

where param 1 is a new JSON document being inserted

ex: db.movieDetails.insertOne({"title":"Frozen 2","year":2019,"countries":["USA","Ireland"]})

If the operation succeed, the MongoDB Shell should return:

{

  "acknowledged" : true,

  "insertedId" : ObjectId("5df15d9d59dafddeaca090a5")   <---- This is an unique ID for the created document

}

2) InsertMany

You can insert many documents at once with this command:

db.[collectionName].insertMany([JSON Array], {ordered : true/false})

where [JSON Array] is a new array containing many documents being inserted by this structure

[{document1}, {document2}, {document3}, ...]

{Ordered Param} is to decide to continue or stop inserting new documents if a run time error caused

true: stop inserting when encountering an error; false: continue inserting even encountering errors.

ex: db.movieDetails.insertMany([ {"title" : "Frozen 4"}, {"title" : "Enchanted"}, {"title" : "Brave"} ],{ordered:true})

// Square brackets indicate Array type