Who should read it: It is for you if you are looking for an overview of this topic for a project, to conduct/appear in an interview, or in general. As I learn more, we will update this article.

MongoDB is a document based, schema-less, and a highly available NOSQL database. Let’s look at some high level details about it.

Basic Terms:

• document: is a basic unit of data equivalent of a row in an RDBMS table.
• collection: is equivalent to a table in an RDBMS database.
• database: A single MongoDB instance can have multiple instances of databases.
• mongo shell: it’s a shell that helps in administrative tasks.

Basic Operations:

CREATE:

• Use insertOne() operation.
• If we need to insert many documents into a collection, use insertMany().
• MongoDB also provide a Bulk Write API, that affects a single collection. It has db.collection.bulkWrite() method which by default performs ordered operations. It also has an option to turn off ordering.

READ:

• Use find() or findOne() operation.

DELETE:

• Use deleteOne() to delete a single document.
• Use deleteMany() to delete all eligible matching documents.

UPDATE:

• For update, we can use updateOne(), updateMany(), or replaceOne().
• updateOne() and updateMany() takes a filter document and a modifier document, as the second parameter.
• replaceOne() expects a document with which it will replace the document with the first input document.

DROP:

• It is possible to use deleteMany() to drop all matching documents in a collection. It can also be used to delete all documents in a collection.
• To clear an entire collection, use of drop() is faster.

UPSERT:

• It is equivalent to update-else-insert. Means, update a matching document. If no matching document found, insert a new document.

Supported Data types: Null, Boolean, Number, String, Date, Regular expression, Array, Embedded document, Object ID, Binary Data, Code

ACID operations: ACID (Atomicity, Consistency, Isolation, Durability) operations in MongoDB are at a document level. Below are some basics of ACID operations:

• Atomicity: zero or none operations.
• Consistency: ensure data is persisted in all nodes.
• Isolation: Any reads or writes are not impacted with other reads or writes.
• Durability: Commits are performed successfully.

References:

• MongoDB: The Definitive Guide, 3rd Edition by by Kristina Chodorow; Eoin Brazil; Shannon Bradshaw
• https://docs.mongodb.com/manual/core/bulk-write-operations/