Database : MongoDB

# SQL (structured query language) / RDBMS (Relational DBMS)
- Table- row (table format) (tabular design)

- table-table relation (primary, foreign key)

- define schema (schema is collection of DB objects associated with one particular DB username. Logical structure of data.)

- insert, fetch, update, remove (CURD) -> Create, Update, Retrieve, Delete

- Example: MySql, MS-SQL (includes defined property (eg. id, name))

# Distributed DBMS (Non- RDBMS)

- Collection (table )-> documents (but no relation)

- No Schema

- Documents (JSON Objects) within collection

- is highly scalable and can includes various property (eg. id, name, address..), can define field

- Example: No SQL type (MongoDB) and nested object

- MongoDB is a general-purpose, doc-based, distributed DB built for modern app developers and for the cloud era. Global cloud DB on AWS, Azure.

-Mongodb automatically set id (object id) unique key (primary key)

Important Command (MongoDB):

1. mongo (shows version and connect to localhost)
2. show dbs (shows list of dbs)
3. use db_name (creating db)
4. db.col_name.insert({

          name: 'Ram',

          addr:{

               perm: 'bkt',

               temp: ['pokhara', 'ktm']

           }})
     5. db.col_name.find({}).pretty() //shows json format with pretty format with nested object 
        db.col_name.find({}).limit(3)
// To find: find, findOne, findById

     6. db.col_name.count() //count the object
     7. update and insert
        db.col_name.update({query_to_find}, {$set: {key_value_pair}}, {multi: true, upsert:true});
     8. db.col.deleteOne( {"_id": ObjectId("id_number")});

     9. db.users.drop()

# DB (MongoDB use)
1. Native MongoDB (driver install)
2. ODM use (mongoose)
- ODM (Object Document Modelling) - Document based DBMS

• schema based solution
• valiadtion (required, unique, ..)
• data type definition -> string, number, boolean, date, ObjectID
• middleware in db
• highly reusable code - db model
• is mongodb object modelling tool designed to work in asyn env. (ODM)

- ORM (Object Relational Mapping) - RDBMS

ORM
- No sql but we make schema using ORM.
- Relational making
- Sequelize (promise-based ORM for Node.js)

# Mongoose (npm i mongoose --save)
- is object data modeling (ODM) library for MongoDB and Node.js
- it manages relationship between data, provides schema validation and is used to translate between an object in code and the representation of those objects in MongoDB.
- Object mapping between node and mongo DB managed via mongoose.
- Schema-based solution (project vision clear)
Mongoose db Connection

1.Event-based (Standard-based)
- Event trigger makes listeners and listeners do execution. eg: Click event
2. Connect Method
3. Create Connection Method

Web Application Development
1. Client-Side (Front End) eg(google material design, twitter bootstrap)
2. Server Side (Back End)

#Mongoose Command (CRUD Operation)
Connection Command
1. mongoose.connect()
2. mongoose.createConnection()
3. Event based
- ensuring connection -> callback and event based solution (.once(), .on())
Insertion
- dbModel.save(callback)
Find
- dbModel.find({query}, callback) //it returns array
- dbModel.findOne({query}, callback) //it returns object
- dbModel.findById(id, callback)
Update
- dbModel.update({query}, $set: {new property & value}, callback);
- db.dbModel.find({}, callback){
         document.name = 'new name';
         document.save(callback);
}
- db.findByIdAndUpdate(id, {new data to be updated}, callback);
Delete
- dbModel.remove({_id:id}, callback)
- dbModel.findByIdAndRemove(id, callback)

# Backup and Restore
Types:
1. bson data (mongodb to mongodb transfer only)
- mongodump
- bson file will be saved.
Command:
a) mongodump
- cd dump
- code .
- all the dbs will be shown
- myprojectdb(our db)
   - products.bson
   - products.metadata.json
- mongorestore
b) bson data restore
- cd ..

Important:
- cmd -- mongodump (backup all db into default dump folder.)
- mongodump --db_name (backup single db)
- mongodump --db db_name (shorthand -d db_name) -o db/backup/db_name(backup single db with other than default folder)
- cd dump - mongorestore --drop db/backup (drop backup db)
-parseIn() -> parse a string and returns an integer.
2. json data
#Backup cmd
mongoexport --db db_name --collection col_name --o path_to_my_backupFolder with jsonfile (.json extension)
Example:  
mongoexport --db myprojectdb --collection users --o new/backup/users.json
json= object

# Restore cmd
mongoimport --db db_name --collection col_name path_to_json_file
Example:
mongoimport --db myprojectdb --collection students users.json

3. csv
# Backup
cmd export -> mongoexport --db db_name collection col_name --type = csv --fields 'comma, separated header name like name, address, phone' --out path_to_save_csvfile (.csv extension for file )
Example:
mongoexport --db myprojectdb collection students --type = csv --fields 'id, username, password, role' --out backup/users.csv
# Restore
mongoimport --db myprojectdb --collection teachers --type = csv backup/abc.csv --headerline (name will be saved from top row)
Example:
mongoimport --db flipkart --type= csv flipkart.csv --headerline

Note: mongodump (backup) and mongorestore (restore) always comes in pair.
mongoexpert and mongoimport always comes in pair
- mongodump (backup) and mongorestore (restore) can not be done. Likewise, mongoexport (backup) and mongorestore(restore) can not be done.

Note: Robomongo (Robo 3D) - UI based DB
MongoDB (compass UI based DB)