Data

Tools

Indexes

Applications

Experiments

Awesome

An open API service indexing awesome lists of open source software.

https://github.com/cheatsheet-lang/mongodb

Cheatsheet for MongoDB
https://github.com/cheatsheet-lang/mongodb

cheatsheet database drop hacktoberfest hacktoberfest2020 mongodb mongotop nosql pipeline retrieve-data schema-less stage syntax

Last synced: about 1 year ago
JSON representation

Cheatsheet for MongoDB

Awesome Lists containing this project

README 

          
# MongoDB Cheatsheet



### General Commands

#### Opens the monogDB shell



```mongo

$ mongo

```



## Commands

### Basics

#### Create and Use Database

```mongo

use ;

```



#### See Default database

```mongo

db;

```



#### Create Collection

```mongo

db.createCollection("");

```



#### Inserting One Document

```mongo

db..insert({name: "Bob", age: 20, desg: "Analytics"});         // Inserting One Document

```



#### Inserting Many Documents

```mongo

db..insertMany([{name: "Alice", age: 30, desg: "Devops"}, {name: "Sue", age: 35, desg: "Full stack"}]);

```



#### Display all Documents

```mongo

db..find();

```



#### Display Documents in JSON Format

```mongo

db..find().pretty();

```



#### Display Distinct

```mongo

db..distinct("name");

```



#### Update Collection

```mongo

db..update({ refKey : "refValue" }, { $set : { changeKey : "changeValue"}})

```

`refKey` and `refValue` refers to the key and value pair from the document which needs to be updated.

`changeKey` and `changeValue` refers to the actual content which needs to be updated.



#### Drop Collection

```mongo

db..drop();

```



### Operations 

#### Projection

When we want to retrieve only specific number of fields from a set of documents, this method is used. 

The fields(keys) we wish to retrieve are passed in find method with true Boolean condition.

If we don’t want to retrieve _id we can hide it by giving false Boolean value to it.

```

db..find({}, key:1, _id:0)

```

#### Limit

If we want to retrieve first specific number of document from a collection this method is used.

The number of elements we wish to retrieve is passed in the limit method.

```

db..find({}, key:1, _id:0).limit(number)

```



#### Skip

Imagine skipping a particular number of documents from a collection while retrieving data.

In such cases, skip method is useful.

```

Query:  db..find({}, key:1, _id:0).skip(number)

```



#### Sort

As the name suggests this method is useful when we wish to retrieve data in a particular manner.

If we want to retrieve data an ascending order, 1 is passed or -1 if descending order. 

```

db..find().sort(refKey:num)

```



### Projection Methods

#### Aggregation :

Aggregations operations process data records and return computed results.

Aggregation operations group values from multiple documents together, and can perform a variety of operations on the grouped data to return a single result.

For the aggregation in MongoDB, you should use `aggregate()` method. 

```

db..aggregate(Aggregate_operation)

```



#### `$project` method :

Passes along the documents with only the specified fields to the next stage in the pipeline. This may be the existing fields from the input documents or newly computed fields.

 

```

{ “$project”: {  } }

```



#### `$match` method :

Filters the documents to pass only the documents that match the specified condition(s) to the next pipeline stage.

```

{ “$match” : {  } }

```



#### `$group` method :

$group is used to group the documents by some specified expression.

```

{ $group: { _id: , : {  :  } } }

```



### Indexing

An index in MongoDB is a special data structure that holds the data of few fields of documents on which the index is created.

####  Apply a new indexing

```

db.collection_name.createIndex({key: 1 or -1})

```

Here, '1' represents ascending order of indexing whereas '-1' descending.



#### Retrieve the index

```

db..getIndexes()

```

####  Drop the existing index

```

db..dropIndexes()

```



### Replication

Replication is the process of synchronizing data across multiple servers. Replication provides redundancy and increases data availability with multiple copies of data on different database servers.

#### Set Up a Replica Set

```

mongod --port "PORT" --dbpath "YOUR_DB_DATA_PATH" --replSet "REPLICA_SET_INSTANCE_NAME"

```

#### Add Members to Replica Set

```

>rs.add(HOST_NAME:PORT)



### Sharding

Sharding is the process of storing data records across multiple machines and it is MongoDB's approach to meeting the demands of data growth.



### Create Backup

#### Dump MongoDB Data

```

>mongodump

```



#### Restore data

```

>mongorestore

```

### Deployment

#### When you are preparing a MongoDB deployment, you should try to understand how your application is going to hold up in production.



```

mongostat

```

#### This command checks the status of all running mongod instances and return counters of database operations.



#### To run the command, start your mongod instance. In another command prompt, go to bin directory of your mongodb installation and type mongostat.

```

D:\set up\mongodb\bin>mongostat

```



```

mongotop

```

#### This command tracks and reports the read and write activity of MongoDB instance on a collection basis. By default, mongotop returns information in each second, which you can change it accordingly.

#### To run the command, start your mongod instance. In another command prompt, go to bin directory of your mongodb installation and type mongotop.

```

D:\set up\mongodb\bin>mongotop

```

#### To change mongotop command to return information less frequently, specify a specific number after the mongotop command.

```mongo

D:\set up\mongodb\bin>mongotop 30

```

#### The above example will return values every 30 seconds.



### Running the commands

To run a command against the current database, use

```mongo

db.runCommand( {  } )

```



To run an administrative command against the admin database, use

```mongo

db.adminCommand( {  } )

```