Technical Architect Brain: MongoDB

MongoDB

MongoDB Feature Card
Queries: It supports ad-hoc queries and document-based queries.
Index Support: Any field in the document can be indexed.
Replication: It supports Master–Slave replication. MongoDB uses native application to maintain multiple copies of data. Preventing database downtime is one of the replica set’s features as it has self-healing shard.

Multiple Servers: The database can run over multiple servers. Data is duplicated to foolproof the system in the case of hardware failure.
Auto-sharding: This process distributes data across multiple physical partitions called shards. Due to sharding, MongoDB has an automatic load balancing feature.
MapReduce: It supports MapReduce and flexible aggregation tools.
Failure Handling: In MongoDB, it’s easy to cope with cases of failures. Huge numbers of replicas give out increased protection and data availability against database downtime like rack failures, multiple machine failures, and data center failures, or even network partitions.
GridFS: Without complicating your stack, any sizes of files can be stored. GridFS feature divides files into smaller parts and stores them as separate documents.
Schema-less Database: It is a schema-less database written in C++.
Document-oriented Storage: It uses BSON format which is a JSON-like format.
Procedures: MongoDB JavaScript works well as the database uses the language instead of procedures.

MongoDB	RDBMS
Document-oriented and non-relational database	Relational database
Document based	Row based
Field based	Column based
Collection based and key–value pair	Table based
Gives JavaScript client for querying	Doesn’t give JavaScript for querying
Relatively easy to setup	Comparatively not that easy to setup
Unaffected by SQL injection	Quite vulnerable to SQL injection
Has dynamic schema and ideal for hierarchical data storage	Has predefined schema and not good for hierarchical data storage
100 times faster and horizontally scalable through sharding	By increasing RAM, vertical scaling can happen

Database Creation

MongoDB doesn’t have any methods to create a database. It automatically creates a database when you save values into the defined collection for the first time. The following command will create a database named ‘database_name’ if it doesn’t exist. If it does exist, then it will be selected.
Command: Use Database_name

Dropping Databases

The following command is used to drop a database, along with its associated files. This command acts on the current database.
Command: db.dropDatabase()

Creating a Collection

MongoDB uses the following command to create a collection. Normally, this is not required as MongoDB automatically creates collections when some documents are inserted.
Command: db.createCollection(name, options)
Name: The string type which specifies the name of the collection to be created
Options: The document type which specifies the memory size and the indexing of the collection. It is an optional parameter.

Showing Collections

When MongoDB runs the following command, it will display all the collections in the server.
Command: In shell you can type: db.getCollectionNames()

$in Operator

The $in operator selects those documents where the value of a field is equal to the value in the specified array. To use the $in expression, use the following prototype:
Command: { field: { $in: [<value1>, <value2>, … <valueN> ] } }

Projection

Often you need only specific parts of the database rather than the whole database. Find() method displays all fields of a document. You need to set a list of fields with value 1 or 0. 1 is used to show the field and 0 is used to hide it. This ensures that only those fields with value 1 are selected. Among MongoDB query examples, there is one which defines projection as the following query.
Command: db.COLLECTION_NAME.find({},{KEY:1})

Date Operator

This command is used to denote time.
Command:
Date() – It returns the current date as a string.
New Date() – It returns the current date as a date object.

$not Operator

$not does a logical NOT operation on the specified <operator-expression> and selects only those documents that don’t match the <operator-expression>. This includes documents that do not contain the field.
Command: { field: { $not: { <operator-expression> } } }

Delete Commands

- Following are commands which explain MongoDB’s delete capabilities.
- Commands:
  collection.remove() – It deletes a single document that matches a filter. db.collection.deleteOne() – It deletes up to only a single document even if the command selects more than one document.
  db.collection.deletemany() – It deletes all the documents that match the specified filter.

Where Command

To pass either a string which has a JavaScript expression or a full JavaScript function to the query system, the following operator can be used.
Command: $where

The forEach Command