The Mongo Shell
Open the command prompt and navigate to
the /bin folder of the MongoDB using the cd command and execute the command mongod there. This will initiate the MongoDB server. We have to
keep this command prompt window alive, as this is running MongoDB.
To stop the MongoDB server, simply enter exit and press Enter.
Now, Open another command prompt and navigate
to the /bin folder of the MongoDB again and execute the
command mongo. This will open up the client to run the MongoDB commands. Please
note that you can exit the Mongo shell by running quit() and the Mongo
daemon by pressing Ctrl + C at any time.
MongoDB: Creating a Database
In the command prompt window in which we ran
the mongo command, after successfully connecting to the mongodb,
just type the command the following :
use database_name
This will create a new database with the
name database_name if there is no database already present
with the same name. If a database already exists with the mentioned name, then
it just connects to that database.
> use studentdb
switched to db studentdb
>
In the above picture, it creates a new database called studentdb and will also connect to the same.
To check the currently connected database, type
in db in the command prompt window, and you will get the name of
the current database as a result.
> db
studentdb
>
To see the list of all the databases in
MongoDB, use command show dbs
> show dbs
admin 0.000GB
config 0.000GB
local 0.000GB
>
Please note that the newly created database studentdb
has not been listed after running the above command. This is because, there
is no records have been inserted into that database yet. Just insert one
record and then run the command again as shown below:
To Insert data, run the following command. Don’t
worry about it, we will learn this in detail in next lessons.
db.studentdb.insert({name : "Pankaj Kapoor" })
NOTE: In
MongoDB, test will be the default database. If no database is created,
then all the data will be stored in the test database.
MongoDB: Drop a
Database
First check the list of databases available as
shown below, using the show dbs command.
> show dbs
admin 0.000GB
config 0.000GB
local 0.000GB
studentdb 0.000GB
test 0.000GB
>
If you want to delete newly created
database studentdb. Run the below command to delete the database.
Before deleting the database, connect to the required database which is to be
deleted.
db.dropDatabase()
> use studentdb
switched to db studentdb
> db.dropDatabase()
{ "dropped" : "studentdb", "ok" : 1 }
>
Now again check the list of databases, to
verify whether the database is deleted or not.
> show dbs
admin 0.000GB
config 0.000GB
local 0.000GB
test 0.000GB
>
Note that the database studentdb has been deleted and hence, it will not be listed in the list of the databases.
MongoDB:
Creating a Collection
In traditional databases, we generally use schema (or tables), but there's no such hard and fast rule for NoSQL Databases. We have Collections instead of Tables. Basically, collections hold the documents or records.
In MongoDB a
collection is automatically created when it is referenced in any command. For
example, if you run an insert command :
db.employee.insert({
name: "Pankaj Kapoor"
})
MongoDB: Creating Collection Explicitly
Above command
will create a collection named student if
it doesn't exist already in the database. But we can explicitly create a
collection using the createCollection() command. The syntax of createCollection method is:
db.createCollection(name, options)
In the above command, name will be the name of the collection and options is a document which can be used to specify configurations for the collection.
Following are the available configuration options for creating a collection in MongoDB:
|
Field |
Type |
Description |
|
capped |
boolean |
(Optional) To create
a capped collection, where in we specify the the maximum size or document
counts to prevent it from growing beyond a set maximum value. |
|
size |
number |
(Optional) To
specify the maximum size in bytes for a capped collection. If a collection is
capped and reaches its maximum size limit, MongoDB then removes older
documents from it to make space for new. |
|
max |
number |
(Optional) This can
be used to specify the maximum number of documents allowed in a capped
collection. |
|
validator |
document |
(Optional) Validates
any document inserted or updated against provided validation rules. |
MongoDB: Creating a Capped Collection
We can create a capped collection using the
following command.
db.createCollection("employee", { capped : true, size : 5242880, max : 2000 } )
This will create a collection named student,
with a maximum size of 5 megabytes and a maximum of 2000 documents.
MongoDB: Drop a Collection
Any collection in a database in MongoDB can be
dropped easily using the following command:
db.collection_name.drop()
drop() method will return true is the collection is dropped
successfully, else it will return false.
