MongoDB and Mongoose Notes

Introduction to MongoDB

1. Definition: MongoDB is an open-source NoSQL database that stores data in JSON-like documents (BSON).

2. NoSQL vs SQL:
   • NoSQL: Developed in late 2000s, focuses on scaling, fast queries, and flexible schemas.
   • SQL: Developed in 1970s, focuses on reducing data duplication, has rigid schemas.

3. Benefits of MongoDB:
   • Flexible data models
   • Horizontal scaling
   • Fast queries
   • Developer-friendly

4. Terminology Comparison:

   RDBMS	MongoDB
   Table	Collection
   Record	Document
   Column	Field
   Joins	Embedded data

5. MongoDB Atlas: Cloud-based database service for MongoDB.

Mongoose ODM

1. Definition: Mongoose is an Object Data Modeling (ODM) library for MongoDB and Node.js.

2. Installation and Setup:

   npm install mongoose
   To use Mongoose in your code:

   const mongoose = require('mongoose');

3. Schema: Defines the structure of documents in a collection.

   Example:

   const companySchema = new Schema({
     companyName: { type: String, unique: true },
     address: String,
     phone: String,
     employeeCount: { type: Number, default: 0 },
     country: String
   });

4. Model: Wrapper for the schema that provides an interface to the database.

   let Company = mongoose.model('companies', companySchema);

5. Connecting to MongoDB:

   mongoose.connect('Your connection string here');

6. Unique Index: Enforces unique values for specific fields.

   Example:

   const userSchema = new Schema({
     username: { type: String, unique: true },
     email: String
   });

   This ensures that no two documents can have the same username.

7. Recursive Schema: Allows nested structures of the same schema.

   Example:

   const commentSchema = new Schema({
     text: String,
     author: String,
     date: { type: Date, default: Date.now }
   });
   commentSchema.add({ replies: [commentSchema] });

   This allows comments to have nested replies.

8. Multiple Connections: Possible to connect to multiple databases.

   Example:

   const conn1 = mongoose.createConnection('mongodb://localhost/db1');
   const conn2 = mongoose.createConnection('mongodb://localhost/db2');
    
   const Model1 = conn1.model('Model1', someSchema);
   const Model2 = conn2.model('Model2', anotherSchema);

   This allows you to work with two different databases simultaneously.

CRUD Operations

1. Create (Save):

   const newCompany = new Company({ ... });
   newCompany.save()
     .then(() => console.log("Saved"))
     .catch(err => console.log(err));

2. Read (Find):

   Company.find({ companyName: 'The Kwik-E-Mart' })
     .exec()
     .then(companies => console.log(companies))
     .catch(err => console.log(err));
   • Can select specific fields: Company.find({}, 'address phone')

3. Update:

   Company.updateOne({ companyName: 'The Kwik-E-Mart' }, { $set: { employeeCount: 3 } })
     .exec()
     .then(() => console.log('Updated'))
     .catch(err => console.log(err));

4. Delete:

   Company.deleteOne({ companyName: 'The Kwik-E-Mart' })
     .exec()
     .then(() => console.log('Deleted'))
     .catch(err => console.log(err));

Best Practices

1. Use .exec() after queries to return a proper promise.

2. Encode passwords with special characters using encodeURIComponent().

   Example:

   const password = "p@ssw0rd!";
   const encodedPassword = encodeURIComponent(password);
   const connectionString = `mongodb+srv://username:${encodedPassword}@cluster0.example.net/mydb`;
   mongoose.connect(connectionString);

   This ensures that special characters in the password don't interfere with the connection string.

3. Handle errors properly in all database operations.

4. Use appropriate update operators like $set, $push, and $addToSet.

   Definition: Update operators are special keys that you can use to modify data in specific ways.

   Examples:

   • $set: Sets the value of a field.

     Company.updateOne({ name: "Acme Inc" }, { $set: { employees: 100 } });

   • $push: Adds an element to an array field.

     User.updateOne({ username: "john" }, { $push: { hobbies: "painting" } });

   • $addToSet: Adds an element to an array field only if it doesn't already exist.

     User.updateOne({ username: "john" }, { $addToSet: { tags: "developer" } });