Master MongoDB: From Basics to Advanced Queries and Aggregations

Preface

MongoDB

is a representative NoSQL database, a high‑performance key‑value store often used for crawler storage.

It is built in C++, provides scalable high‑performance data storage for web applications, and combines features of relational databases.

Connection

Format:

mongodb://username:password@host:port/database

mongodb://

: fixed prefix, required. username:password: authentication; password may be omitted. host: required server address. port: defaults to 27017 if omitted. database: defaults to test if omitted.

Creating Database and Collection

Create a database

> use underground_station
switched to db underground_station

If the database exists, the command switches to it; otherwise it creates it.

List databases

> show dbs
admin   0.000GB
config  0.000GB
local   0.000GB

In MongoDB a database appears in the list only after it contains data.

Create a collection

> db.createCollection("Quotations")
{ "ok" : 1 }

The collection is created successfully.

Show collections

> show collections
Quotations

Insert Documents

MongoDB stores data as documents; a collection is analogous to a table.

Insert a single document:

> use underground_station
switched to db underground_station

> db.Quotations.insert({
   name: 'Jia Gui',
   description: 'I owe enough meals for two years',
   createDate: '2021-04-15'
})
WriteResult({ "nInserted" : 1 })

Insert multiple documents:

> db.Quotations.insertMany([
   {name:'Gold Mark', description:'This weight is also boiled', createDate:'2021-04-15'},
   {name:'Jia Gui', description:'I fought him with my head and face', createDate:'2021-04-16'},
   {name:'Hei Teng', description:'Who am I? I am Hei Teng', createDate:'2021-04-16'},
   {name:'Sun Youfu', description:'No water, no fish; no you, no donkey', createDate:'2021-04-17'}
])

Update Documents

Update a single document:

> db.Quotations.update({name:'Hei Teng'}, {$set:{name:'Hei Teng', description:'All traitors are stupid', createDate:'2021-04-16'}})

Update multiple documents (multi flag):

> db.Quotations.update({name:'Jia Gui'}, {$set:{description:'I don\'t know, I just know she looks great', createDate:'2021-04-16'}}, {multi:true})

Upsert (insert if not exists):

> db.Quotations.update({name:'Sae River'}, {$set:{name:'Sae River', description:'Go east, cause trouble'}}, {upsert:true})

Delete Documents

Delete all documents matching a condition:

> db.Quotations.remove({name:'Jia Gui'})
WriteResult({ "nRemoved" : 2 })

Delete all documents in a collection:

> db.Quotations.remove({})

Query Documents

General find syntax: db.collection.find(query, projection) Example: exclude _id field: > db.Quotations.find({}, {'_id':0}) AND query (implicit):

> db.Quotations.find({name:'Gold Mark', createDate:'2021-04-26'})

OR query (explicit):

> db.Quotations.find({$or:[{name:'Jia Gui'},{description:'All traitors are stupid'}]})

Combined AND/OR:

> db.Quotations.find({createDate:'2021-04-18', $or:[{name:'Jia Gui'},{description:'All traitors are stupid'}]})

Advanced Queries

Range operators: $lt, $gt, $lte, $gte, $ne, $in, $nin.

Example: documents with createDate greater than 2021-04-17:

> db.Quotations.find({createDate: {$gt: '2021-04-17'}})

Regular expression query:

> db.Quotations.find({name: {$regex: 'Gold'}})

Aggregation

Sorting

> db.Quotations.find({}, {_id:0}).sort({createDate:-1})

Grouping

Group by name and sum a numeric field forceValue:

> db.Quotations.aggregate([
   {$match:{createDate: {$gt:'2021-04-07'}}},
   {$group:{_id:"$name", forceValue: {$sum:"$forceValue"}}}
])

Similar examples for $avg, multi‑field grouping, and other aggregation operators are shown.

For more advanced usage, refer to the official MongoDB documentation.