mongoose indexing? grouping? - mongodb

Question

I'm kinda new to mongoose, and I'm not sure if it's a right term.
what I'm building is a community site (like redit), and I have a schema like below
const postSchema = new mongoose.Schema({
content: {
type: String,
required: true,
},
title: {
type: String,
required: true,
},
userId: {
type: mongoose.Schema.Types.ObjectId,
required: true,
ref: 'User',
},
board: {
type: String,
required: true,
enum: ['board1','board2'],
},
created_at: {
type: Date,
default: Date.now,
},
updated_at: {
type: Date,
},
})
there are many kinds of 'board'
and I'm not sure if it can be 'indexed'.
purpose of it is for getting posts faster
for example in sql (assume that board column is indexed)
--> select * from post where board = 'board1' ;
I'm confusing about the terms, need some direction..

Answer 1

Short answer:
You need to create an index on the field board by doing:
db.post.createIndex(
{ board: 1 } ,
{ name: "borad index" }
)
Long answer:
Indexing in mongodb uses memory in order to save running time.
Let's take an example: say you have all words in English in your DB. And you are reading a book and from time to time you need to search for a word to check its meaning.
How would you do that? A dictionary. You'll sort the words alphabetically and then you could easily search for every word you wanted.
Indexing apply the same concept. When you create an index on the field board it takes all its values, sort them and save it in a table (and reference for each entry the full document from your collection).
Now when you search for select * from post where board = 'board1' it first use the memorized table of sorted boards, finds the ones that equal to board1 and then by the reference gives you the full documents that belongs to it. You can continue reading here.