Find Method with Conditions

The find() Method

To query data from MongoDB collection, you need to use MongoDB's find() method.

Syntax

Basic syntax of find() method is as follows

>db.COLLECTION_NAME.find()

find() method will display all the documents in a non structured way.

The pretty() Method

To display the results in a formatted way, you can use pretty() method.

Syntax:

>db.mycol.find().pretty()

Example

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

Apart from find() method there is findOne() method, that reruns only one document.

RDBMS Where Clause Equivalents in MongoDB

To query the document on the basis of some condition, you can use following operations

Operation	Syntax	Example	RDBMS Equivalent
Equality	{<key>:<value>}	db.mycol.find({"by":"tutorials point"}).pretty()	where by = 'tutorials point'
Less Than	{<key>:{$lt:<value>}}	db.mycol.find({"likes":{$lt:50}}).pretty()	where likes < 50
Less Than Equals	{<key>:{$lte:<value>}}	db.mycol.find({"likes":{$lte:50}}).pretty()	where likes <= 50
Greater Than	{<key>:{$gt:<value>}}	db.mycol.find({"likes":{$gt:50}}).pretty()	where likes > 50
Greater Than Equals	{<key>:{$gte:<value>}}	db.mycol.find({"likes":{$gte:50}}).pretty()	where likes >= 50
Not Equals	{<key>:{$ne:<value>}}	db.mycol.find({"likes":{$ne:50}}).pretty()	where likes != 50

AND in MongoDB

Syntax:

In the find() method if you pass multiple keys by separating them by ',' then MongoDB treats it AND condition. Basic syntax of AND is shown below:

>db.mycol.find({key1:value1, key2:value2}).pretty()

Example

Below given example will show all the tutorials written by 'tutorials point' and whose title is 'MongoDB Overview'

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

For the above given example equivalent where clause will be ' where by='tutorials point' AND title='MongoDB Overview' '. You can pass any number of key, value pairs in find clause.

OR in MongoDB

Syntax:

To query documents based on the OR condition, you need to use $or keyword. Basic syntax of OR is shown below:

>db.mycol.find(
   {
      $or: [
      {key1: value1}, {key2:value2}
      ]
   }
).pretty()

Example

Below given example will show all the tutorials written by 'tutorials point' or whose title is 'MongoDB Overview'

>db.mycol.find({$or:[{"by":"tutorials point"},{"title": "MongoDB Overview"}]}).pretty()
{
   "_id": ObjectId(7df78ad8902c),
   "title": "MongoDB Overview", 
   "description": "MongoDB is no sql database",
   "by": "tutorials point",
   "url": "http://www.tutorialspoint.com",
   "tags": ["mongodb", "database", "NoSQL"],
   "likes": "100"
}
>

Using AND and OR together

Example

Below given example will show the documents that have likes greater than 100 and whose title is either 'MongoDB Overview' or by is 'tutorials point'. Equivalent sql where clause is'where likes>10 AND (by = 'tutorials point' OR title = 'MongoDB Overview')'

>db.mycol.find({"likes": {$gt:10}, $or: [{"by": "tutorials point"},{"title": "MongoDB Overview"}]}).pretty()
{
   "_id": ObjectId(7df78ad8902c),
   "title": "MongoDB Overview", 
   "description": "MongoDB is no sql database",
   "by": "tutorials point",
   "url": "http://www.tutorialspoint.com",
   "tags": ["mongodb", "database", "NoSQL"],
   "likes": "100"
}
>

---

The insert() Method in MongoDB

The insert() Method

To insert data into MongoDB collection, you need to use MongoDB's insert() orsave()method.

Syntax

Basic syntax of insert() command is as follows:

>db.COLLECTION_NAME.insert(document)

Example

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

Here mycol is our collection name, as created in previous tutorial. If the collection doesn't exist in the database, then MongoDB will create this collection and then insert document into it.

In the inserted document if we don't specify the _id parameter, then MongoDB assigns an unique ObjectId for this document.

_id is 12 bytes hexadecimal number unique for every document in a collection. 12 bytes are divided as follows:

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

To insert multiple documents in 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: 'http://www.tutorialspoint.com',
   tags: ['mongodb', 'database', 'NoSQL'],
   likes: 100
},
{
   title: 'NoSQL Database', 
   description: 'NoSQL database doesn't have tables',
   by: 'tutorials point',
   url: 'http://www.tutorialspoint.com',
   tags: ['mongodb', 'database', 'NoSQL'],
   likes: 20, 
   comments: [ 
      {
         user:'user1',
         message: 'My first comment',
         dateCreated: new Date(2013,11,10,2,35),
         like: 0 
      }
   ]
}
])

To insert the document you can use db.post.save(document) also. If you don't specify _idin the document then save() method will work same as insert() method. If you specify _id then it will replace whole data of document containing _id as specified in save() method.

---

The drop() Method in MongoDB

The drop() Method

MongoDB's db.collection.drop() is used to drop a collection from the database.

Syntax:

Basic syntax of drop() command is as follows

db.COLLECTION_NAME.drop()

Example:

First, check the available collections into your database mydb

>use mydb
switched to db mydb
>show collections
mycol
mycollection
system.indexes
tutorialspoint
>

Now drop the collection with the name mycollection

>db.mycollection.drop()
true
>

Again check the list of collections into database

>show collections
mycol
system.indexes
tutorialspoint
>

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

---

The createCollection() Method in MongoDB

The createCollection() Method

MongoDB db.createCollection(name, options) is used to create collection.

Syntax:

Basic syntax of createCollection() command is as follows

db.createCollection(name, options)

In the command, name is name of collection to be created. Options is a document and used to specify configuration of collection

Parameter	Type	Description
Name	String	Name of the collection to be created
Options	Document	(Optional) Specify options about memory size and indexing

Examples:

Basic syntax of createCollection() method without options is as follows

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

You can check the created collection by using the command show collections

>show collections
mycollection
system.indexes

Following example shows the syntax of createCollection() method with few important options:

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

In mongodb you don't need to create collection. MongoDB creates collection automatically, when you insert some document.

>db.tutorialspoint.insert({"name" : "tutorialspoint"})
>show collections
mycol
mycollection
system.indexes
tutorialspoint
>

The dropDatabase() Method in MongoDB

The dropDatabase() Method

MongoDB db.dropDatabase() command is used to drop a existing database.

Syntax:

Basic syntax of dropDatabase() command is as follows:

db.dropDatabase()

This will delete the selected database. If you have not selected any database, then it will delete default 'test' database

Example:

First, check the list available databases by using the command show dbs

>show dbs
local      0.78125GB
mydb       0.23012GB
test       0.23012GB
>

If you want to delete new database <mydb>, then dropDatabase() command would be as follows:

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

Now check list of databases

>show dbs
local      0.78125GB
test       0.23012GB
>

---

The use Command in MongoDB

The use Command

MongoDB use DATABASE_NAME is used to create database. The command will create a new database, if it doesn't exist otherwise it will return the existing database.

Syntax:

Basic syntax of use DATABASE statement is as follows:

use DATABASE_NAME

Example:

If you want to create a database with name <mydb>, then use DATABASE statement would be as follows:

>use mydb
switched to db mydb

To check your currently selected database use the command db

>db
mydb

If you want to check your databases list, then use the command show dbs.

>show dbs
local     0.78125GB
test      0.23012GB

Your created database (mydb) is not present in list. To display database you need to insert atleast one document into it.

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

In mongodb default database is test. If you didn't create any database then collections will be stored in test database.