Day 10: Cassandra Lab Practice – Data Modeling

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✅ Day 10: Data Modeling in Cassandra

🎯 Objective:

Understand how to model data in Cassandra using query-first design – designing tables based on how you query, not how data is structured relationally.

📘 1. Key Principles of Cassandra Data Modeling

  • Query-based design: Every table supports one query pattern.
  • Denormalization is OK: Duplicate data for different queries.
  • Avoid joins and multi-table operations
  • One table per query pattern is common

📊 2. Real-World Use Case Example

Use Case: Online Learning App

Entities:

  • Students
  • Courses
  • Enrollments
  • Attendance
  • Assessments

🔧 3. Sample Table Designs

➤ Table 1: student_by_id

Query: Get student details by ID

CREATE TABLE test_lab.student_by_id (
  student_id uuid PRIMARY KEY,
  name text,
  email text,
  enrolled_on timestamp
);

➤ Table 2: courses_by_student

Query: List all courses for a student

CREATE TABLE test_lab.courses_by_student (
  student_id uuid,
  course_id text,
  course_name text,
  instructor text,
  PRIMARY KEY ((student_id), course_id)
);

➤ Table 3: attendance_by_class

Query: Get attendance by class and date

CREATE TABLE test_lab.attendance_by_class (
  class_id text,
  attendance_date date,
  student_id uuid,
  status text,
  PRIMARY KEY ((class_id, attendance_date), student_id)
);

⚖️ 4. Denormalized Table for Assessments

CREATE TABLE test_lab.assessments_by_course (
  course_id text,
  student_id uuid,
  exam_type text,
  marks int,
  PRIMARY KEY ((course_id), student_id, exam_type)
);

📌 5. Modeling Guidelines Recap

Relational Concept Cassandra Strategy
Normalize Denormalize
Join Create separate table
Foreign Keys Not used in Cassandra
ACID Transactions Design around partitions

🧪 Day 10 Lab Tasks

  1. Design 3–4 tables for a simple application (blog, app, school, store)
  2. Use proper partition and clustering keys
  3. Avoid joins – assume each table is optimized for a specific query
  4. Practice inserting sample data and running sample queries

✅ Checklist

Task Done
Understood query-first design ✅
Created tables for multiple query patterns ✅
Used compound partition & clustering keys ✅
Avoided relational modeling concepts ✅


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