myxozoa / mongodb-cheatsheet

MongoDB CheatSheet

(TODO: Impliment in React + Mongo)

Document

---

Analogous to item. A single entry in a collection. A JSON object.

• cannot start with a dollar sign > $ (as this specifies a field path or an operator)
• cannot contain a dot > .
• cannot have null
• maximum size: 16mb

Field

A name-value pair in a document. (Analogous to key-value).

Collection

---

A collection of documents. In my head this is what I think of as a database.

Database

---

Basically a collection (container) of collections. Every database has its own file set.

Indexes

---

Data structures that store small parts of the collection's data that you set so that Mongo can search without scanning every single document in that collection.

// $lt is the query criteria
// users is the collection
db.users.find( { score: { "$lt": 30 } } ).sort( { score: -1 } );

                                       Here
                                        V
+---------------+----------------+---------------+---------------+----------------+
| {             | {              | {             | {             | {              |
|     score: 1  |     score: 15  |     score: 30 |     score: 35 |     score: 100 |
| }             | }              | }             | }             | }              |
+---------------+----------------+---------------+---------------+----------------+

ObjectId

---

12-byte id generated automatically that displays in hexadecimal.

Shard(ing)

---

Distributing a mongo server, to individual shards