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The college enrollment system: Joining JSON Schema

Learning Outcomes:
JOINING JSON Schema

MongoDB Demo Lab: College Enrollment System

1. Collection Structures:

// students collection
{
studentId: String,
name: String,
email: String,
program: String,
enrollmentDate: Date
}

// courses collection
{
courseId: String,
courseName: String,
credits: Number,
department: String,
prerequisites: [String]
}

// enrollments collection
{
enrollmentId: String,
studentId: String,
courseId: String,
semester: String,
grade: String,
status: String
}

2. Demo Queries:

// Find all courses a student is enrolled in
db.enrollments.aggregate([
{
$match: { studentId: "ST101" }
},
{
$lookup: {
from: "courses",
localField: "courseId",
foreignField: "courseId",
as: "courseDetails"
}
}
]);

// Get complete enrollment information by student projected to: course details
db.enrollments.aggregate([
{
$lookup: {
from: "students",
localField: "studentId",
foreignField: "studentId",
as: "studentInfo"
}
},
{
$lookup: {
from: "courses",
localField: "courseId",
foreignField: "courseId",
as: "courseInfo"
}
}
]);


How the College Enrollment System Works

Today, we'll be diving into the College Enrollment System, a practical application of MongoDB to model and manage real-world data.
Understanding how this system works will not only prepare you for managing complex data relationships but will also build the foundation for designing enterprise applications like the United Earth Space Exploration Command system you’ll tackle in your assignment.
Let’s break it down step by step, explaining each component of the system and how it fits together.
⁠

1. Overview of the College Enrollment System

Imagine we are managing a college's enrollment system digitally.
The system keeps track of three key entities:
Students: Who is enrolled at the college.
Courses: What classes the college offers.
Enrollments: The link between students and courses, storing details of which student is taking which course, and additional information like semester and grades.
MongoDB’s ability to store flexible, schema-less data makes it a perfect candidate for managing these interconnected relationships.
⁠

2. Structure of the Data

To handle this system, we create three collections in MongoDB:

a. Students Collection

This stores information about each student:
studentId: Unique identifier for the student.
name: The student’s full name.
email: Their email address.
program: The academic program they are enrolled in.
enrollmentDate: When they joined.
Example document:
{
studentId: "ST101",
name: "John Doe",
email: "john.doe@example.com",
program: "Computer Science",
enrollmentDate: ISODate("2023-09-01")
}

⁠

b. Courses Collection

This represents the courses taught at the college:
courseId: Unique course identifier.
courseName: The name of the course.
credits: The number of credits the course provides.
department: Which academic department it belongs to.
prerequisites: Other courses a student must complete before taking this one.
Example document:
{
courseId: "CS101",
courseName: "Introduction to Programming",
credits: 3,
department: "Computer Science",
prerequisites: []
}

⁠

c. Enrollments Collection

At the heart of the system, this collection links students to the courses they’ve enrolled in:
enrollmentId: Unique ID for each enrollment.
studentId: Links to the studentId field in the students collection.
courseId: Links to the courseId field in the courses collection.
semester: Indicates the semester during which the student is enrolled.
grade: Records their final grade for the course.
status: Whether the enrollment is Active, Dropped, or Completed.
Example document:
{
enrollmentId: "EN1001",
studentId: "ST101",
courseId: "CS101",
semester: "Fall 2023",
grade: "A",
status: "Completed"
}
⁠

3. How the System Works Together

The enrollments collection acts as a bridge between students and courses.
Joining Collections (via $lookup):
A lookup operation allows us to retrieve related data from one collection into another. For example:
To find all courses a specific student is enrolled in.
To enrich enrollment records with detailed information on students and courses.
⁠

4. Examples of Queries

a. Find All Courses Taken by a Student

Here’s how we use $lookup to find all the courses a student is enrolled in:
db.enrollments.aggregate([
{
$match: { studentId: "ST101" } // Filter enrollments for the specific student
},
{
$lookup: {
from: "courses", // The "courses" collection to join with
localField: "courseId", // The field in "enrollments" to match
foreignField: "courseId", // The field in "courses" to match
as: "courseDetails" // Alias for the resulting nested array
}
}
]);
How it works:
The query first filters the enrollments for a specific studentId.
$lookup pulls matching courseId records from the courses collection.
The results include all relevant course details within a courseDetails array.
⁠

b. Enrich Enrollment Data with Student and Course Info

You can join students, enrollments, and courses to create a complete view:
db.enrollments.aggregate([
{
$lookup: {
from: "students",
localField: "studentId",
foreignField: "studentId",
as: "studentInfo"
}
},
{
$lookup: {
from: "courses",
localField: "courseId",
foreignField: "courseId",
as: "courseInfo"
}
}
]);

How it works:
The first $lookup includes detailed information about the student (from the students collection).
The second $lookup pulls in data about the course (from the courses collection).
The enriched enrollment provides a complete picture: the student, the course, and how they connect.
⁠

5. Advantages of MongoDB for This System

Here’s why MongoDB works so well for this type of system:
Flexibility:
MongoDB handles schema-less data, so you can easily add new fields or relationships as the system evolves.
Efficiency:
$lookup provides powerful ways to fetch related data directly, eliminating the need for multiple queries.
Scalability:
Collections can handle large amounts of data, perfect for growing student and course datasets.
Real-World Modeling:
The flexibility of JSON-like documents maps well to how real-world entities interact (students taking courses, etc.).
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