Let Us see how to Perform simple MongoDB Queries such as create, insert, update, delete, drop

In this section, we will see how to create a database and collection in MongoDB.

Create MongoDB Database

The use Command

MongoDB use DATABASE_NAME is used to make a database. The command will create a new database if it does not exist, otherwise, it’ll return the present database.

Syntax For Creating New Database

The Basic syntax of use database statement is as follows –

use DATABASE_NAME

for Example, if you want to use the database names as `movie_collection` then the following statement will be used

>use movie_collection
switched to db movie_collection

If you want to check which database is been currently used. you can use this following statement –

>db
movie_collection

and if you want to check all the list of the database, you can use this following command

>show dbs
local     0.78125GB
test      0.23012GB

Your created database (movie_collection) is not present in the list. To display database, you need to insert at least one document into it.

>db.movie.insert({"name":"Crypto"})
>show dbs
local      0.78125GB
mydb       0.23012GB
test       0.23012GB

The createCollection() Method In MongoDB

for creating a collection in MongoDB the method createCollection(name, options) is used.
For Example

db.createCollection(name, options)

In the above method, the name is the name of collection which needs to b created. where else option is the document and is used to specify the configuration of a collection.

Following table shows the list of options you can use in method createCollection(name, options) .

MongoDB initial checks size field of capped collection, then it checks max field while inserting the document

Examples

The basic syntax of the method createCollection() without options is as follows −

>use movie_collection
switched to db movie_collection
>db.createCollection("popular_movies")
{ "ok" : 1 } 

The method createCollection() without options is as follows −

>db.createCollection("mycol", { capped:true, autoIndexId:true, size:6142800, max:10000 } )
{ "ok" : 1 }
>

In this section, we will see how to drop a database and collection in MongoDB.

Drop MongoDB Database

The dropDatabase() Method

To drop an existing database in MongoDB db.dropDatabase() method is used.

Syntax –

db.dropDatabase()   

The above method will delete the selected database. If you haven’t selected any database, then it will delete the default ‘test’ database.

The drop() Method In MongoDB

To drop an existing collection in MongoDB db.collection.drop() method is used.

Syntax –

>db.movie_collection.drop()
true 

drop() method will return true, if the selected collection is dropped successfully, otherwise it will return false.

In this section, we will see how to insert a document in MongoDB.

The insert() Method In MongoDB

We can use insert() or save() method to insert data into MongoDB collection

Example –

>db.mycol.insert({
    _id: ObjectId(7df78ad8902c),
    title: 'MongoDB Overview', 
    description: 'MongoDB is no sql database',
    by: 'tutorials point',
    url: 'https://www.geekstrick.com',
    tags: ['mongodb', 'database', 'NoSQL'],
    likes: 100
})

Here mycol is our collection name, as created in the previous chapter. If the collection does not exist within the database, then MongoDB can create this collection and then insert a document into it.
In the inserted document, if we do not specify the aid parameter, then MongoDB assigns a unique ObjectId for this document.
_id is twelve bytes hex number unique for every document in a collection. twelve bytes are divided as follows

_id: ObjectId(4 bytes timestamp, 3 bytes machine id, 2 bytes process id, 3 bytes incrementer)

Passing Array of document

To insert multiple documents in a single query, you can pass an array of documents in insert() command.

Example –

>db.post.insert([
{
    title: 'MongoDB Overview', 
    description: 'MongoDB is no sql database',
    by: 'tutorials point',
    url: 'https://www.geekstrick.com',
    tags: ['mongodb', 'database', 'NoSQL'],
    likes: 100
},   
{
    title: 'NoSQL Database', 
    description: "NoSQL database doesn't have tables",
    by: 'tutorials point',
    url: 'https://www.geekstrick.com',
    tags: ['mongodb', 'database', 'NoSQL'],
    likes: 20, 
    comments: [	
        {
            user:'user1',
            message: 'Its a comment',
            dateCreated: new Date(2013,11,10,2,35),
            like: 0 
        }
    ]
}
])

To insert the document you’ll be able to use db.post.save(document) also. If you do not specify child in the document then save() method will work same as insert() method. If you specify child then it will replace whole data of document containing child as specified in save() method.

MongoDB Update() Method

MongoDB’s update() and save() methods are used to update document into a collection. The update() method updates the values in the existing document while the save() method replaces the existing document with the document passed in save() method.

Example

Consider the mycol collection has the following data.

{ "_id" : ObjectId(5983548781331adf45ec5), "title":"MongoDB Overview"}
{ "_id" : ObjectId(5983548781331adf45ec6), "title":"NoSQL Overview"} 

Following example will set the new title ‘New MongoDB Tutorial’ of the documents whose title is ‘MongoDB Overview’.

>db.mycol.update({'title':'MongoDB Overview'},{$set:{'title':'New MongoDB Tutorial'}})
>db.mycol.find()
{ "_id" : ObjectId(5983548781331adf45ec5), "title":"New MongoDB Tutorial"}
{ "_id" : ObjectId(5983548781331adf45ec6), "title":"NoSQL Overview"} 
>

To update multiple documents, you need to set a parameter ‘multi’ to true.

>db.mycol.update({'title':'MongoDB Overview'},
{$set:{'title':'New MongoDB Tutorial'}},{multi:true}) 

The remove() Method in MongoDB

In this section we will see how to delete a document using MongoDB.

MongoDB’s remove() method is used to remove a document from the collection. remove() method accepts 2 parameters. One is deletion criteria and second is justOne flag.

• deletion criteria – (Optional) deletion criteria according to documents will be removed.
• justOne – (Optional) if set to true or 1, then remove only one document.

Remove Only One

If there are multiple records and you want to delete only the first record, then set justOne parameter in remove() method.

>db.COLLECTION_NAME.remove(DELETION_CRITERIA,1)

Remove All Documents

If you don’t specify deletion criteria, then MongoDB will delete whole documents from the collection. This is equivalent of SQL’s truncate command.

>db.mycol.remove()
>db.mycol.find()
>

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