In this tutorial, we will find quick answers to the some of the basic questions related with MongoDB database.
All the MongoDB statements given in this article is tested in MongoDB shell version 2.2.2.
Listing all the existing databases in MongoDB?
>show dbs
Creating a new MongoDB database?
>use university
The above command opens the database university , if it exists. Other wise a new database will be created with the name university, provided a new collection is created in it before exiting Mongo shell.
Exiting Mongo shell?
>exit
Showing currently opened database?
>db
Creating a new collection in MongoDB database?
Syntax
db.createCollection(name, { size : ..., capped : ..., max : ... } )
Example
>db.createCollection("students")
Inserting a document into a collection with insert() method?
Syntax
db.students.insert(obj)
Example
>db.students.insert(
... {
... name:"Rajesh",
... age:21,
... gender:"M",
... course:"BTECH",
... marks:81
... }
... )
Retrieving all the existing documents from a collection?
Syntax
db.students.find([query],[fields])
Example
>db.students.find()
{ "_id" : ObjectId("50cd99b62e85f03ba01adafb"), "name" : "Rajesh", "age" : 21, "gender" : "M", "course" : "BTECH", "marks" : 81 }
Inserting a document into a collection with save() method?
Syntax
db.students.save(obj)
Example
>db.students.save(
... {
... name:"John",
... age:21,
... gender:"M",
... course:"BTECH",
... marks:79
... })
Inserting multiple documents into a collection with single statement?
Syntax
db.students.insert(obj)
Example
>db.students.insert([
... { name:"Firoz", age:22,gender:"M",course:"BTECH",marks:88 },
... { name:"Alan", age:21, gender:"M", course:"BTECH", marks:68 },
... { name:"Dev", age:20, gender:"M", course:"MBA", marks:61 } ,
... { name:"Aishwarya", age:21, gender:"F", course:"MBA", marks:72 }
... ])
Retrieving all the existing documents from a collection?
Syntax
db.students.find([query],[fields])
Example
>db.students.find()
{ "_id" : ObjectId("50cd99b62e85f03ba01adafb"), "name" : "Rajesh", "age" : 21, "gender" : "M", "course" : "BTECH", "marks" : 81 }
{ "_id" : ObjectId("50cd99f22e85f03ba01adafc"), "name" : "John", "age" : 21, "gender" : "M", "course" : "BTECH", "marks" : 79 }
{ "_id" : ObjectId("50cd9b38d0262f1b85a3fc57"), "name" : "Firoz", "age" : 22, "gender" : "M", "course" : "BTECH", "marks" : 88 }
{ "_id" : ObjectId("50cd9b38d0262f1b85a3fc58"), "name" : "Alan", "age" : 21, "gender" : "M", "course" : "BTECH", "marks" : 68 }
{ "_id" : ObjectId("50cd9b38d0262f1b85a3fc59"), "name" : "Dev", "age" : 20, "gender" : "M", "course" : "MBA", "marks" : 61 }
{ "_id" : ObjectId("50cd9b38d0262f1b85a3fc5a"), "name" : "Aishwarya", "age" : 21, "gender" : "F", "course" : "MBA", "marks" : 72 }
Updating documents in a collection of MongoDB database?
Syntax
>db.students.update(query,object<,options>)
Example : Updating marks of Dev to 67
>db.students.update(
... { name:"Dev" },
... { $set:{marks:67} },
... { upsert:true, multi:true }
... )
Note :
If upsert is true, then new row will be inserted provided no matching document corresponding to query is found.
If multi is true, then multiple documents matching the query will be updated.
Deleting documents from a collection?
Syntax
db.collection.remove( <query>, <justOne> )
Example : Deleting all MBA students
>db.students.remove({course:"MBA"},false)
Note :
If <justOne> is true, then only one row will be deleted.
If <justOne> is false, then multiple rows will be deleted.
Final list of documents in students collection
>db.students.find()
{ "_id" : ObjectId("50cebdcc984024d0901bad60"), "name" : "Rajesh", "age" : 21, "gender" : "M", "course" : "BTECH", "marks" : 81 }
{ "_id" : ObjectId("50cebe81984024d0901bad61"), "name" : "John", "age" : 21, "gender" : "M", "course" : "BTECH", "marks" : 79 }
{ "_id" : ObjectId("50cebeccb73c3219ce6f4bb4"), "name" : "Firoz", "age" : 22, "gender" : "M", "course" : "BTECH", "marks" : 88 }
{ "_id" : ObjectId("50cebeccb73c3219ce6f4bb5"), "name" : "Alan", "age" : 21, "gender" : "M", "course" : "BTECH", "marks" : 68 }
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