Basic Operations in MongoDB

Examples

Below are various MongoDB statements.

Three database commands you should know.

show dbs – List all databases.

use db_name – Switches to db_name.

show collections – List all tables in the current selected database.

Help:

At last, uses help() to guide you how to do things in MongoDB.

All available commands.

db.help() – Shows help on db.
db.collection.help() – Shows help on collection (table).
db.collection.function.help() – Shows help on function.

Create:

Implicitly created on first insert() operation. The primary key_id is automatically added if _id field is not specified.

db.users.insert( {
    user_id: "abc123",
    age: 55,
    status: "A"
 } )

However, you can also explicitly create a collection:
db.createCollection("users")

Alter:

Collections do not describe or enforce the structure of its documents; i.e. there is no structural alteration at the collection level. However, at the document level,
update() operations can add fields to existing documents using the $set operator.
db.users.update(
    { },
    { $set: { join_date: new Date() } },
    { multi: true }
)
update() operations can remove fields from documents using the $unset operator.

db.users.update(
    { },
    { $unset: { join_date: "" } },
    { multi: true }
)

Create Index:

db.users.ensureIndex( { user_id: 1 } )

db.users.ensureIndex( { user_id: 1, age: -1 } )

db.users.ensureIndex({username:1},{unique:true});

Fetch Indexes:

db.users.getIndexes()

Drop Index:
db.users.dropIndex({username:1})

Drop Collection:
db.users.drop()

Select:
db.users.find ()

db.users.find (
    { },    { user_id: 1, status: 1 }
)
db.users.find (   
 { },    { user_id: 1, status: 1, _id: 0 }
)
db.users.find ({ status: "A" })

Specified Columns:
db.users.find(
    { status: "A" },    { user_id: 1, status: 1, _id: 0 }
)

Not Equal:
db.users.find(
    { status: { $ne: "A" } }
)

AND:
db.users.find(
    { status: "A",
      age: 50 }
)

OR:
db.users.find(
    { $or: [ { status: "A" } ,
             { age: 50 } ] }
)

Greater:
db.users.find(
    { age: { $gt: 25 } }

)

Less:

db.users.find(

   { age: { $lt: 25 } }

)

Greater and Less:
db.users.find(
   { age: { $gt: 25, $lte: 50 } }
)

Like:
db.users.find( { user_id: /bc/ } )
db.users.find( { user_id: /^bc/ } )

Sort ASC:
db.users.find( { status: "A" } ).sort( { user_id: 1 } )

Sort DESC:
db.users.find( { status: "A" } ).sort( { user_id: -1 } )

Count:
db.users.count()
or
db.users.find().count()

db.users.count( { user_id: { $exists: true } } )
or
db.users.find( { user_id: { $exists: true } } ).count()

db.users.count( { age: { $gt: 30 } } )
or
db.users.find( { age: { $gt: 30 } } ).count()

Distinct:
db.users.distinct( "status" )

Limited Results:
db.users.findOne()
or
db.users.find().limit(1)

db.users.find().limit(5).skip(10)

Explain:

db.users.find( { status: "A" } ).explain()

Update Records:
db.users.update(
   { age: { $gt: 25 } },
   { $set: { status: "C" } },
   { multi: true }
)
db.users.update(
   { status: "A" } ,
   { $inc: { age: 3 } },
   { multi: true }
)
Delete Rcords:
db.users.remove( { status: "D" } )
db.users.remove({})