MongoDB is a document-oriented NoSQL database used for high-volume data storage. It came into light around the mid-2000s.
Each database contains collections which in turn contain documents.
- Each document can be different, with a varying number of fields.
The document structure aligns with how developers construct their classes and objects in their respective programming languages.
The rows (or documents as called in MongoDB) don’t need to have a schema defined beforehand. Instead, the fields can be created on the fly.
The data model available within MongoDB allows you to represent hierarchical relationships, to store arrays, and other more complex structures more quickly.

Components

_id: – This is a field required in every MongoDB document.
- The _id field represents a unique value and is like the document’s primary key.
- If you create a new document without an _id field, MongoDB will automatically create the field.
Collection: This is a grouping of MongoDB documents.
- It is the equivalent of a table that is created in any other RDMS.
- A collection exists within a single database.
Cursor: This is a pointer to the result set of a query.
- Clients can iterate through a cursor to retrieve results.
Database: This is a container for collections like in RDMS wherein it is a container for tables.
- Each database gets its own set of files on the file system.
Document: A record in a MongoDB collection and in turn, it will consist of field names and values.
Field: A name-value pair in a document.
- A document has zero or more fields.
- Fields are analogous to columns in relational databases.

Collections

MongoDB creates new collections when you first store data for the collections.
By default, a collection does not require its documents to have the same schema.
- Starting in MongoDB 3.2, you can enforce document validation rules for a collection during update and insert operations.

A MongoDB view is a read-only queryable object whose contents are defined by an aggregation pipeline on other collections or views.
- MongoDB does not persist the view contents to disk. A view's content is computed on-demand when a client queries the view.
- MongoDB provides two different view types: standard views and on-demand materialized views.
- Standard views are computed when you read the view and are not stored on disk.
- On-demand materialized views are stored on and read from disk.

MongoDB stores data records as BSON documents.
- BSON is a binary representation of JSON documents, though it contains more data types than JSON.