This document discusses schema design and CRUD operations in MongoDB. It compares MongoDB and MySQL, and covers how to create databases and collections in MongoDB. It then describes various CRUD operations like create, read, update and delete. Finally, it discusses schema design considerations like one-to-one, one-to-many and many-to-many relationships, and recommends denormalizing data for better read performance.

1. Schema Design & CRUD
Ahmed Elbassel
Email: elbassel.n13@gmail.com
Skype: ahmed_elbassel

2. Schema design & CRUD
- MongoDB Vs MySql
- Create database and collection
- MongoDB client
- CRUD operations
- Schema Design
- Denormalizing for schema design

3. MongoDB Vs MySql
MySql MongoDB
Table Collection
Row Document
Column Field
Joins Embedded documents, linking

4. Create Database
- Connect to MongoDB, open terminal and run:
- > mongo
- Then you’re using the mongo console, and you’re able to run mongo queries
- To show all databases: > show dbs
- To connect or create a database: > use myDB
- To show collections: > show collections
- To create a collection: > db.createCollection(‘collection name’)

5. - RoboMongo
- MongoBooster
- MongoChef
MongoDB client

6. CRUD Operations - Create
- Create a document:
- db.users.insertOne({name:'ahmed',lname:'bassel'});
- To insert many: db.users.insert([ {..........},{ ..........}, {...........}]);
- If you tried to insert a document with existing _id, it will throw duplicate _id error
- Insert using save: > db.users.save({......})
- If the inserted object does not have an id, then a new object will be inserted.
- If the object has an id, it will replace the object that match the id in the
database.

7. CRUD Operations - Read
- Reading documents, use find({query}) method:
- > db.users.find()
- To make it look pretty: > db.users.find().pretty()
- To get users by name: db.users.find{'name':'ahmed'}
- And Operator: - Or operator
- Using And & Or together
- Get by name and (email or username)

8. CRUD Operations - Update
- We can use save and update methods.
- Save method is the same previous one.
- Update:
- Query: The selection criteria for the update.
- Update: The modifications to apply.
- Options:
- upsert: Optional. If set to true, creates a new document when no document matches the
query criteria. The default value is false.
- multi: Optional. If set to true, updates multiple documents that meet the query criteria. If
set to false, updates one document, The default value is false.
- writeConcern and collation: advanced, will be discussed in a MongoDB course.

9. CRUD Operations - Update
- The update() method either modifies specific fields in existing documents or
replaces an existing document entirely.
- Update Specific Fields: to use update operator such as, $set
- Update operators: https://docs.mongodb.com/manual/reference/operator/update/#id1
- Replace a document entirely:

10. CRUD Operations - Delete
- To delete a document, use this method:
- Query: The selection criteria for the update.
- justOnce:To limit the deletion to just one document, set to true. Omit to use the default value
of false.
- writeConcern and collation: advanced.

11. Schema Design - One to One
- It’s better to embed it one document into the other.
- You should have a logical reason why you make them individually.

12. Schema Design - One to Many
- You should know how much Many:
- One to few(less than 100): then embed the
few into the one
- One to Many(Thousands): then add array of
foreign keys into the one

13. Schema Design - One to Many
- One to Too many:
- Then you add a foreign key into the many.

14. Denormalization for Schema design
- You can mix between the three previous methods, putting foreign keys in both
one and many.
- Trade off: Reading VS Writing:
- If you need to read more than write, then denormalize your data.
- In other words store what you query for.

15. Questions