How to Execute Database Query in MongoDB

MongoDB is an open-source, cross-platform, document-oriented database. It is a NoSQL database. It works on collection and documentation.

A single MongoDB database has multiple databases. In MongoDB, data is stored in JSON-style documents.

MySQL vs MongoDB

1) MySQL contains tables, but MongoDB contains collections.

2) MySQL contains rows, but MongoDB contains documents.

3) MySQL contains columns, but MongoDB contains fields.

4) MySQL contains Table joins, but MongoDB contains Embedded Documents.

5) In MySQL, we define one column as the primary key, but in MongoDB primary key (default key _id) is provided by MongoDB itself.

Useful Database Queries in MongoDB:

1) use the DATABASE_NAME command is used to create a database.

Example:

>use hdfc
switched to db mydb

2) db command is used to check the currently selected database.

Example:

>db
mydb

3) show the dbs command to check all database lists.

Example:

>show dbs
local     0.78125GB
test      0.23012GB

In the above example database, name is not shown in the list. To display the list, you have to insert at least one document in hdfc database.

Example:

>db.customer.insert({name:"customerName",amount:20000})
>show dbs
local      0.78125GB
mydb      0.23012GB
test       0.23012GB

Note: By default database in MongoDB is a test, if you don’t create any database, then the collection will be stored in the test database.

4) db.dropDatabase() command is used to drop a currently working database.

Example: 

>use hdfc
switched to db mydb
>db.dropDatabase()
>{ "dropped" : "mydb ", "ok" : 1 }
>

5) db.createCollection(name, options) command is used to create collection. The collection works here similarly to the table works in MYSQL.

Collections are created automatically when we insert data into the database. There is no need to create a collection in the database.

Example:

>use test
switched to db test
>db.createCollection("customer")
{ "ok" : 1 }
>

6) show collections command is used to show all collections/tables.

Example:

>show collections
customer
>

7) db.collection.drop() command is used to drop a collection from the database. drop() method will return true if the selected collection is dropped successfully, otherwise, it will return false.

Example:

db.customer.drop()
true
>

8) db.COLLECTION_NAME.insert(document) command is used to insert data in MongoDB collection. It is used when you don’t have any _id in the document. If you have _id in the document then the save() method will be used.

Example:

db.customer.insert([
{
name: ' customerName ',
amount: 20000
},
{
name: ' customerName 2',
amount: 10000
}
])

Example:

db.customer.save([
{
_id: ObjectId(7df78ad8902c),
name: ' customerName ',
amount: 20000
},
{
_id: ObjectId(7df78ad8902c),
name: ' customerName 2',
amount: 10000
}
])

9) db.COLLECTION_NAME.find() command is used to get all data of collection. It displays data in a non-structural way.

Example:

>db.customer.find()

10) db.COLLECTION_NAME.find().pretty() command is used to get all data of collection in a structural way.

Example:

>db.customer.find().pretty()
{
_id: ObjectId(7df78ad8902c),
name: ' customerName ',
amount: 20000
}
>

11) db.COLLECTION_NAME.update(SELECTION_CRITERIA, UPDATED_DATA) command is used to update values in the Document/Row. By default update() method in MongoDB, update only one Document. If we want to update multi Documents/Rows at a time, we need to set the parameter ‘multi’ to true.

Example of single Document updation:

>db.mycol.update({'name':'Jorge’},{$set:{'name':'Dan’}}

Example of Multi Documents updation:

>db.mycol.update({'name':'Jorge},
{$set:{'name':’Dan '}},{multi:true})

12) db.COLLECTION_NAME.save({_id:ObjectId(),NEW_DATA}) command is used to save a new document in place of an existing document.

Example:

>db.mycol.save(
{
"_id" : ObjectId(7df78ad8902c), "name":"Dan",
"amount":10000
}
)

13) db.COLLECTION_NAME.remove(DELLETION_CRITTERIA, JUSTONE) command is used to remove the document from the collection.

DELLETION_CRITTERIA(optional): DELLETION_CRITTERIA parameter includes a document that will be removed according to the criteria.

Example:

>db.mycol.remove({'name': customerName '})

JUSTONE(optional): JUSTONE parameter includes true or 1. It removes only one document. JUSTONE parameter deletes only one record at a time in multiple records.

Example:

>db.mycol.remove({'name':' customerName '},1)

If we don’t write any parameter inside remove() method then MongoDB deletes all documents from the collection. This works as a TRUNCATE command works in MYSQL.

Example:

>db.mycol.remove()

14) db.COLLECTION_NAME.find().limit(NUMBER) command set the limit of the document that we want to be displayed.

Example:

>db.mycol.find({},{"name":1,_id:0}).limit(2)
{"name":" customerName "}
{"name":" customerName 2"}
>

We hope you understand the overview of MongoDB and can implement MongoDB in projects easily. Contact us if you want to implement MongoDB in your application.