Formulating MongoDB Queries - database

Question

Hello members of stackoverflow, I'm totally new to mongoDB hence I'm having trouble with formulating some queries in it. I've been trying to do it for quite some time but have failed to do so. Please refer to the following code:
#create database
use db_m_1
#create collection (all tables in database)
db.createCollection('articles')
#this is your article in noSQL
#change this according to your info
article = {
_id: '1',
title: 'article1',
date_published: ISODate("2014-09-17T23:25:56.314Z"),
written_by: [{
_id: '1',
name: 'Osama'
}],
comments: [{
_id: '1',
content: 'This is very good article',
date: ISODate("2014-09-17T23:25:56.314Z"),
comment_by: {
_id: '1',
name: 'Osama'
password: 'pass'
}
}]
}
#this is used to insert
db.articles.insert(article)
#queries
#1-- know which comments were made on article 'a beginning' and by whom
#create query
let q1 = {
title: 'a beginning'
}
#create projection
db.articles.find(q1, {"Comments.username": 1, "Comments.comment_content": 1})
#2-- which staff members were working on article 'sample'
let q2 = {
title: 'sample'
}
let p2 = {
written_by: 1
}
db.articles.find(q2, p2);
#5-- which articles were written in 2014
let q5 = {
date_published: new Date("2014-10-01T00:00:00.000Z")}
}
q5 = {date_published: new Date("2014-05-13T00:00:00.000+00:00")}
let p5 = {
title: 1,
written_by: 1
}
I need help with query 3 and 4.
3-- how many articles has each staff member worked on?
4-- which staff members have worked on more than one article with maximum number of article writing staff on top
Thank you. :)

Answer 1

3-- how many articles has each staff member worked on?
4-- which staff members have worked on more than one article with
maximum number of article writing staff on top
These two aggregations solve the queries 3 and 4 respectively.
# 3
db.articles.aggregate( [
{
$unwind: "$written_by"
},
{
$group: {
_id: "$written_by.name",
count: { $sum: 1 }
}
},
{
$project: {
name: "$_id",
_id: 0,
count: 1
}
}
] )
# 4
db.articles.aggregate( [
{
$unwind: "$written_by"
},
{
$group: {
_id: "$written_by.name",
count: { $sum: 1 }
}
},
{
$match: {
count: { $gt: 1 }
}
},
{
$project: {
name: "$_id",
_id: 0,
count: 1
}
},
{
$sort: { count: -1 }
}
] )
Some test data:
article1 = {
_id: '1',
title: 'article1',
date_published: ISODate("2014-09-17T23:25:56.314Z"),
written_by: [ {
_id: '1',
name: 'Osama'
} ],
comments: [ {
_id: '1',
content: 'This is very good article',
date: ISODate("2014-09-17T23:25:56.314Z"),
comment_by: {
_id: '1',
name: 'Osama',
password: 'pass'
}
} ]
}
article2 = {
_id: '2',
title: 'article2',
written_by: [ {
_id: '9',
name: 'Krish'
},
{
_id: '1',
name: 'Osama'
} ],
comments: "..."
}

Answer 2

the data structure you use isn't proper for this kind of queries. I recommend you to have one collection per your entities, for this example we need 3 collections with these schema:
// article doc schema
{
_id: int,
title: String,
date_published: ISODate,
};
// writer doc schema
{
_id: int,
name: String,
articles_ids: [int]
};
// comment doc schema
{
_id: int,
content: String,
date: ISODate,
by_id: int,
article_id: int
};
by this way you can make complex queries, and you have to use aggregate query for your need. here is some examples:
// Query 03
// how many articles has each staff member worked on?
let piplines = [
{
// separate writers by their names
$group: {
_id: "$name",
totalArticles: { $size: "$articles_ids" }
}
}
];
let arrayOfStaffStates = writerCollection.aggregate(piplines);
// Query 04
// which staff members have worked on more than one article
let piplines = [
{
// separate writers by their names
$group: {
_id: "$name",
totalArticles: { $size: "$articles_ids" }
},
// match they who have more than 1 articles
$match: {
totalArticles: { $gte: 1 }
}
}
];
let stuffs = writerCollection.aggregate(piplines);