In this chapter, we will learn how to query documents from the MongoDB collection.
The find() Method
To query data from MongoDB collection, you need to use MongoDB’s find() method.
Syntax
The basic syntax of the find() method is as follows −
>db.COLLECTION_NAME.find()
find() method will display all the documents in a non-structured way.
Example
Assume we have created a collection named mycol as −
> use sampleDB
switched to db sampleDB
> db.createCollection("mycol")
{ "ok" : 1 }
>
And inserted 3 documents in it using the insert() method as shown below −
> db.mycol.insert([
{
title: "MongoDB Overview",
description: "MongoDB is no SQL database",
by: "adglob",
url: "https://www.adglob.in",
tags: ["mongodb", "database", "NoSQL"],
likes: 100
},
{
title: "NoSQL Database",
description: "NoSQL database doesn't have tables",
by: "adglob",
url: "http://adglon.in",
tags: ["mongodb", "database", "NoSQL"],
likes: 20,
comments: [
{
user:"user1",
message: "My first comment",
dateCreated: new Date(2013,11,10,2,35),
like: 0
}
]
}
])
Following method retrieves all the documents in the collection −
> db.mycol.find()
{ "_id" : ObjectId("5dd4e2cc0821d3b44607534c"), "title" : "MongoDB Overview", "description" : "MongoDB is no SQL database", "by" : "adglob", "url" : "https://www.adglob.in", "tags" : [ "mongodb", "database", "NoSQL" ], "likes" : 100 }
{ "_id" : ObjectId("5dd4e2cc0821d3b44607534d"), "title" : "NoSQL Database", "description" : "NoSQL database doesn't have tables", "by" : "adglob", "url" : "https://www.adglob.in", "tags" : [ "mongodb", "database", "NoSQL" ], "likes" : 20, "comments" : [ { "user" : "user1", "message" : "My first comment", "dateCreated" : ISODate("2013-12-09T21:05:00Z"), "like" : 0 } ] }
>
The pretty() Method
To display the results in a formatted way, you can use pretty() method.
Syntax
>db.COLLECTION_NAME.find().pretty()
Example
Following example retrieves all the documents from the collection named mycol and arranges them in an easy-to-read format.
> db.mycol.find().pretty()
{
"_id" : ObjectId("5dd4e2cc0821d3b44607534c"),
"title" : "MongoDB Overview",
"description" : "MongoDB is no SQL database",
"by" : "adglob",
"url" : "https://www.adglob.in",
"tags" : [
"mongodb",
"database",
"NoSQL"
],
"likes" : 100
}
{
"_id" : ObjectId("5dd4e2cc0821d3b44607534d"),
"title" : "NoSQL Database",
"description" : "NoSQL database doesn't have tables",
"by" : "adglob",
"url" : "https://www.adglob.in",
"tags" : [
"mongodb",
"database",
"NoSQL"
],
"likes" : 20,
"comments" : [
{
"user" : "user1",
"message" : "My first comment",
"dateCreated" : ISODate("2013-12-09T21:05:00Z"),
"like" : 0
}
]
}
The findOne() method
Apart from the find() method, there is findOne() method, that returns only one document.
Syntax
>db.COLLECTIONNAME.findOne()
Example
Following example retrieves the document with title MongoDB Overview.
> db.mycol.findOne({title: "MongoDB Overview"})
{
"_id" : ObjectId("5dd6542170fb13eec3963bf0"),
"title" : "MongoDB Overview",
"description" : "MongoDB is no SQL database",
"by" : "adglob",
"url" : "https://www.adglob.in",
"tags" : [
"mongodb",
"database",
"NoSQL"
],
"likes" : 100
}
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>:{$eg;<value>}} | db.mycol.find({“by”:”adglob”}).pretty() | where by = ‘adglob’ |
| Less Than | {<key>:{$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”:{$ne:50}}).pretty() | where likes != 50 |
| Values in an array | {<key>:{$in:[<value1>, <value2>,……<valueN>]}} | db.mycol.find({“name”:{$in:[“Raj”, “Ram”, “Raghu”]}}).pretty() | Where name matches any of the value in :[“Raj”, “Ram”, “Raghu”] |
| Values not in an array | {<key>:{$nin:<value>}} | db.mycol.find({“name”:{$nin:[“Ramu”, “Raghav”]}}).pretty() | Where name values is not in the array :[“Ramu”, “Raghav”] or, doesn’t exist at all |
AND in MongoDB
Syntax
To query documents based on the AND condition, you need to use $and keyword. Following is the basic syntax of AND −
>db.mycol.find({ $and: [ {<key1>:<value1>}, { <key2>:<value2>} ] })
Example
Following example will show all the tutorials written by ‘adglob’ and whose title is ‘MongoDB Overview’.
> db.mycol.find({$and:[{"by":"adglob"},{"title": "MongoDB Overview"}]}).pretty()
{
"_id" : ObjectId("5dd4e2cc0821d3b44607534c"),
"title" : "MongoDB Overview",
"description" : "MongoDB is no SQL database",
"by" : "adglob",
"url" : "https://www.adglob.in",
"tags" : [
"mongodb",
"database",
"NoSQL"
],
"likes" : 100
}
>
For the above given example, equivalent where clause will be ‘ where by = ‘adglob’ 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. Following is the basic syntax of OR −
>db.mycol.find(
{
$or: [
{key1: value1}, {key2:value2}
]
}
).pretty()
Example
Following example will show all the tutorials written by ‘adglob’ or whose title is ‘MongoDB Overview’.
>db.mycol.find({$or:[{"by":"adglob"},{"title": "MongoDB Overview"}]}).pretty()
{
"_id": ObjectId(7df78ad8902c),
"title": "MongoDB Overview",
"description": "MongoDB is no sql database",
"by": "adglob",
"url": "https://www.adglob.in",
"tags": ["mongodb", "database", "NoSQL"],
"likes": "100"
}
>
Using AND and OR Together
Example
The following example will show the documents that have likes greater than 10 and whose title is either ‘MongoDB Overview’ or by is ‘adglob’. Equivalent SQL where clause is ‘where likes>10 AND (by = ‘adglob’ OR title = ‘MongoDB Overview’)’
>db.mycol.find({"likes": {$gt:10}, $or: [{"by": "adglob"},
{"title": "MongoDB Overview"}]}).pretty()
{
"_id": ObjectId(7df78ad8902c),
"title": "MongoDB Overview",
"description": "MongoDB is no sql database",
"by": "adglob",
"url": "https://www.adglob.in",
"tags": ["mongodb", "database", "NoSQL"],
"likes": "100"
}
>
NOR in MongoDB
Syntax
To query documents based on the NOT condition, you need to use $not keyword. Following is the basic syntax of NOT −
>db.COLLECTION_NAME.find(
{
$not: [
{key1: value1}, {key2:value2}
]
}
)
Example
Assume we have inserted 3 documents in the collection empDetails as shown below −
db.empDetails.insertMany(
[
{
First_Name: "Radhika",
Last_Name: "Sharma",
Age: "26",
e_mail: "radhika_sharma.123@gmail.com",
phone: "9000012345"
},
{
First_Name: "Rachel",
Last_Name: "Christopher",
Age: "27",
e_mail: "Rachel_Christopher.123@gmail.com",
phone: "9000054321"
},
{
First_Name: "Fathima",
Last_Name: "Sheik",
Age: "24",
e_mail: "Fathima_Sheik.123@gmail.com",
phone: "9000054321"
}
]
)
Following example will retrieve the document(s) whose first name is not “Radhika” and last name is not “Christopher”
> db.empDetails.find(
{
$nor:[
40
{"First_Name": "Radhika"},
{"Last_Name": "Christopher"}
]
}
).pretty()
{
"_id" : ObjectId("5dd631f270fb13eec3963bef"),
"First_Name" : "Fathima",
"Last_Name" : "Sheik",
"Age" : "24",
"e_mail" : "Fathima_Sheik.123@gmail.com",
"phone" : "9000054321"
}
NOT in MongoDB
Syntax
To query documents based on the NOT condition, you need to use $not keyword following is the basic syntax of NOT −
>db.COLLECTION_NAME.find(
{
$NOT: [
{key1: value1}, {key2:value2}
]
}
).pretty()
Example
Following example will retrieve the document(s) whose age is not greater than 25
> db.empDetails.find( { "Age": { $not: { $gt: "25" } } } )
{
"_id" : ObjectId("5dd6636870fb13eec3963bf7"),
"First_Name" : "Fathima",
"Last_Name" : "Sheik",
"Age" : "24",
"e_mail" : "Fathima_Sheik.123@gmail.com",
"phone" : "9000054321"
}
