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Understand relationships in Rell

In this course, we will explore data modelling and creating relationships between entities using the Rell language. Our goal is to help you understand table relationships and use them to build efficient and scalable applications.

We assume you have a basic understanding of SQL, including table relationships and joins. We will show you how to implement these concepts using Rell, a powerful language for managing data structures. You will learn to translate your SQL knowledge into Rell and create robust and scalable data models.

By the end of this course, you will have a solid understanding of data modelling with Rell, enabling you to build advanced applications with efficient data architecture. Get ready to enhance your skills and take your applications to the next level!

What we will learn​

In this course, we will explore how to implement different types of relationships in Rell:

  • One-to-one
  • One-to-many
  • Many-to-many

We will discuss creating and using these relationships to build functional applications. Additionally, we will cover the following types of joins:

  • Inner Join
  • Outer Join

Concept and structure of our application​

We will create a library management application that will include the following main entities:

  • Library: Information about the library, its address, and shelves.
  • Shelf: The number of the shelf and the books it holds.
  • Book: The title, authors, and reviews of the book.
  • Author: The name of the author and the books they have written.
  • Member: The name of the member and the books they have borrowed.
  • Loan: Information about borrowed books, including loan and return dates.

Implementation details​

  1. One-to-one relationship
    • Library - address: Each library has one address.
  2. One-to-many relationship
    • Library - shelves: A library can have many shelves.
    • Shelf - books: A shelf can hold many books.
  3. Many-to-many relationship
    • Book - authors: A book can have many authors, and an author can write many books.
    • Member - loans: A member can borrow many books, and many members can borrow a book through loans.

Entity-relationship diagram​

Advantages of Rell​

  • Simplicity: Rell syntax is clean and easy to understand. You can define relationships without getting bogged down by the complexities of foreign keys and constraints.
  • Readability: Rell code is more readable and maintainable, making it easier to understand the structure of your database at a glance.
  • Error reduction: By abstracting away the manual management of keys and constraints, Rell reduces the potential for errors and inconsistencies in your database design.

The complete code repository for this course is available here: Relationships course repository.

What's next?​

In the following lessons, we will examine these entities and their relationships in detail. We will learn how to create these relationships in Rell and perform different operations with the records. By the end of the course, you will be able to create a fully functional library management application demonstrating your understanding of relational database relationships.