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Cover image for MongoDB: Nooks and Crannies
Abayomi Ogunnusi
Abayomi Ogunnusi

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MongoDB: Nooks and Crannies

#mongodb #beginners #devjournal #tutorial

Database manipulation and querying can be time-consuming, and as developers, we require a database that is both flexible and capable of speeding up our development process.

Today, we'll look at how to use MongoDB, one of the most popular NoSQL databases.



Table Of Content


Prerequisite

🎯 MongoDB and mongoshell installed. Download

🎯 Add MongoDB path to your environment variable

Checking MongoDB is installed correctly

To check if you have MongoDB correctly installed and added to your environment variable, run mongo --version in your terminal.

Result:
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Start a MongoDB server

Method 1:

You can also run mongosh on your terminal if you install the new mongo shell. Click here to download

Result:
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Method 2:

On your terminal run mongo.exe
Result:
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Now that we have confirmed MongoDB installation let's see how we can navigate around MongoDB .

To view db 

 show dbs
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To view collections 

show collections
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To use a db: 

use [database name]
use blog
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Delete an entire db 

db.dropDatabase()
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Exit out of the terminal 

exit 
Ctrl + C
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Data Types in Mongodb

Mongodb uses BSON i.e key value pairs

{
    string:"strings",
    int:405,
    double: 3.565,
    boolean: true, || false
    array: [1,23,4,5]
    object:{attr1: "", attr2:"",attr3:""},
    date:new Date("YYYY-mm-dd"),
    no_value: null
}
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Create collection 

db.createCollection([collection name])
db.createCollection("students")
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Drop a collection 

db.students.drop()
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Insert One document (a json object) into A COLLECTION 

db.students.insertOne({name: "Abayomi", age:4, email:"joe@gmail.com"})
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Result: The _id is the unique identifier.

Breakdown: the {name: "Abayomi"} is called a Document and it lives inside the collection i.e every object stored in a collection in db is called a document.

Insert nested object 

db.students.insertOne({name: "yomi", age:56, address:{street:"ajaka makun"}, hobbies:["gyming"]})
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clear screen 

(Ctrl + L)
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You can generate custom id 

db.students.insertOne({name: "joan", age:56, _id:256})
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Adding arrays 

db.students.insertOne({name: "jinx", hobbies: ["sking", "fighting"]})

db.students.insertOne({name: "jinx", hobbies: ["sking", "fighting"], contact: 0808083423, startDate: new Date("2020-08-89")})
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Insert multiple records using arrays of objects 

db.students.insertMany([{name: "jude", age:9}, {name: "james", age:78}, {name: "amry", age:239}])
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Finding and querying Documents

Find all: 

db.students.find({})
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Turn a specific field off 

db.students.find({}, {_id:0})
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Limit query 

db.students.find({}, {_id:0}).limit(2)
This removes all _id
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Sort query 

db.students.find({}, {_id:0}).sort({name: 1})
1 means ascending order
-1 means descending order
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The name is arranged alphabetically
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Sort by multiple fields 

db.students.find({}, {_id:0}).sort({age: -1, name: 1})
1= asacending order
-1 = descending order
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Find using filtering using where queries 

db.students.find({age: 4}, {_id:0}).sort({name: 1, age:-1})
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Skipping entries 

db.students.find().skip(1).sort({age: 1, name: 1}).limit(2)
This skips the first entry gotten from he database
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Filtering using multiple fields 

db.students.find({name: "joan", age: 56})
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Select syntax 

db.students.find({}, {name: 1, age: 1, _id: 0})
This selects only the name and age property it will not populate other info like address and hobbies and also omits the _id property
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OR operator $or logic 

db.students.find({$or: [{name:"abayomi"}, {age:56}]}, {_id:0})
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Greater operator $gt than logic 

db.students.find({age:{$gt: 10}})
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This gets every fields with age grater than 10.
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Less than or equal to $lte 

db.students.find({age:{$lte: 10}}).sort({age: -1})
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Other comparison operator worth of note: $eq, $ne,


In operator $in 

db.students.find({name: {$in:["Abayomi", "joan"]}})
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  • Finds every data that has name has Abayomi and joan

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Mixing complex queries 

db.students.find({age:{ $gte:9, $lt:240} })
Here we are saying age is less than 10, greater than 36
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Not query 

db.students.find({age:{$not:{$lte:34}}})
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* This gets all ages not less than or equal to 34

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Accessing nested objects and getting specific array 

db.students.find({"address.street": "ajaka makun"})
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Count documents 

db.students.countDocuments({age:{$lte: 23}})
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Update data 

db.students.updateOne({name: "joan"}, {$set:{name:"Joana Sisily"}})
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Update with id 

db.students.updateOne({_id: ObjectId("622875510fc8edaf452c0e13")}, {$set:{age:459}})
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Find by id 

db.students.findOne({_id: ObjectId("6199abeeb73c785f519a29e3")})
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* Returns null if id not found

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Increment 

db.students.updateOne({_id: ObjectId("622875f90fc8edaf452c0e15")}, {$inc:{age:9}})
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This increment the age value by 9, the initial value is 9, final value will be 18

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#### Renaming fields

db.students.updateOne({_id: ObjectId("622875f90fc8edaf452c0e15")}, {$rename:{age:"studentAge"}}))
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Not-in operator

This negates the output

db.students.find({name: {$nin:["Abayomi", "joan"]}})
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Check if field or data exists 

1) db.students.find({name: {$exists: true}})
2) db.students.find({major: {$exists: false}}, {_id:0})
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  • Ex 2: Returns nothing


BSON indexing

To return data type using BSON indexing i.e strings is 2.

db.students.find({name: {$type: 2}})
2 means strings: this will return all name fields that is strings
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source


Check specific array entries

i.e target specific element in an array

Get arrays size

i.e if an elements has 4 , 5, 6 etc elem in it

db.students.find({hobbies: {$size: 2}})
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Element Match

Check match and return a matching element in an array

db.students.find({hobbies: {$elemMatch: {$eq: "sking"}}})
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Update many records 

updates all instance of the name:mimi
db.students.updateMany({name: "mimi"},{$set: {name:"miracle"}})
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Replace a field completely 

db.students.replaceOne({name: "Abayomi"},{name: "Joseph abayomi", age: 90, student: true})
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Delete records

db.collectionName.action

db.students.deleteMany({}) ==> deletes all
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Delete with a query params 

db.students.deleteMany({name: "xu"})
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Delete one 

db.students.deleteOne({name: "xu"})
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Bulk Write

perform multiple action update, delete, insert in one command

db.students.bulkWrite(
      [
         { insertOne :
            {
               "document" :
               {
                  name: "James", occupation: "Developer"
               }
            }
         },
         { insertOne :
            {
               "document" :
               {
                  name: "Travesy", occupation: "backend"
               }
            }
         },
         { updateOne :
            {
               filter : { name : "James" },
               update : { $set : { occupation: "content-writer"} }
            }
         },
         { deleteOne :
            { filter : { name : "Abayomi"} }
         },
         { replaceOne :
            {
               filter : { name : "James" },
               replacement : { name: "James Bond", }
            }
         }
    ],
    {ordered: false}
   );
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Text indexing

This is synonymous to a search bar on the client-side


db.students.insertMany([{name: "John", desc: "Young and fair"},{name: "Doe", desc: "fair but young and silly"}, {name: "Dare", desc: "young and beautiful "}])
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Create text indexing 

db.students.createIndex( { name: "text", desc: "text" } )
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db.students.find({ $text: {$search: "fair" } })
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Let's attach precedence score to search query
db.students.find(
   { $text: { $search: "Young and fair" } },
   { score: { $meta: "textScore" } }
).sort( { score: { $meta: "textScore" } } )
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Aggregation 


db.students.insertMany([{item : "pencil", total: 10.75, student: "Wick"}, {item : "pen", total: 50, student: "John"}, {item : "book", total: 11.33, student: "Thanos"}, {item : "ruler", total: 8.50, student: "Thanos"}, {item : "book", total: 4.75, student: "James"}, {item : "pen", total: 4.75, student: "Wick"}, {item : "bag", total: 4.75, studstudent: "John"}])
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Get total counts of books 

db.students.countDocuments({item: "pen"})
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Get total amount of money spent by a student 

db.students.aggregate(
     [
          {$match: {} },
          {$group: {_id: "$student", total: { $sum: "$total"} } }
     ]
)
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Find how much has been spent on each item and sort it by price 

db.students.aggregate(
     [
          {$match: {} },
          {$group: {_id: "$item", total: { $sum: "$total"} } },
          {$sort: {total: -1}}
     ]
)
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Find how much money each customer has spent on book and pen 

db.students.aggregate(
     [
          {$match: {item: {$in: ["book", "pen"]} } },
          {$group: {_id: "$item", total: { $sum: "$total"} } },
     ]
)
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Resources

Bson types reference
Aggregation Reference
mongodb website
Mike Dane

Top comments (2)

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marcomoscatelli profile image
Marco Moscatelli •

This is a great tutorial for beginners, well done!

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drsimplegraffiti profile image
Abayomi Ogunnusi •

@moscatellimarco Thanks

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