Northwind Elixir Traders
Northwind Elixir Traders
A practical tutorial on databases with Elixir, Ecto, and SQLite
About the Book
This is a book for the curious and the explorers.
Step back into the nostalgic realm of 90s database exploration and learning with a modern twist! Remember the "Northwind Traders" database from the early days of Microsoft Access? It's back and ready for a reimagining in the dynamic world of the Elixir programming language and its Ecto database layer.
Join me on a learning exploration as we transform the familiar "Northwind Traders" into the captivating "Northwind Elixir Traders" through database migrations, table alterations, schema definitions, CRUD operations, references, queries, changesets and the core of what you need to use Ecto productively.
This isn't your typical Ecto tutorial. Instead of pursuing the usual "happy path" reflected in the official documentation and "Getting Started" guide, we'll dive into the complexities and nuances of database implementation, offering a refreshing exploration that goes beyond the ordinary.
Our adventure begins by embracing the simplicity of SQLite3 over the conventional choice of Postgres. This deliberate trade-off in favor of simplicity against feature-completeness introduces challenges and roadblocks that will enrich your learning experience as we navigate through the intricacies of schema design, migrations, primary and foreign keys, relational structures between the different tables, and queries that return meaningful insights.
Discover the joy of experimentation as we encounter unexpected hurdles and exercize our Elixir skills in figuring out why things don't work as expected, and how to still get things done, regardless. Through these challenges, you'll gain invaluable insights into problem-solving and critical thinking with Elixir and Ecto.
Embrace the ethos of fearless exploration as we delve deeper into Ecto's capabilities, focusing on the art of reading documentation and adapting to unforeseen obstacles. With each chapter, you'll elevate your understanding of Ecto, empowering yourself to tackle real-world database projects with confidence and finesse instead of with copy-paste operations and hopes and wishes that it all works out in the end.
For a curious Elixir newcomer delving into the world of building databases for a microservice, a backend, or a Phoenix or Phoenix LiveView app, "Northwind Elixir Traders" promises an immersive learning experience that's both enriching and unforgettable.
About the Author
Reader Testimonials
Petros Papapanagiotou, PhD
Head of Development
This rare gem of a technical book is a must-read for anyone wanting to build practical skills in modeling databases with Elixir and Ecto. But it’s not only about coding—it also emphasizes real-world problem-solving, learning by doing, and tackling development roadblocks head-on with confidence, in a relentless pursuit of understanding. Truly, an invaluable resource for everyone tired of cookie-cutter tutorials and theoretical fluff!
Table of Contents
- Before we begin
- About this book
- Our journey along the book’s chapters
- Foreword
- Preface
- Chapter 1: Our objective, the application and the repo
- Creating the repository (the “repo”)
- The need for a supervision tree
- Summary and outlook
- Chapter 2: Creating the database schema
- Building the Northwind Elixir Traders database
- Preparing and using the data structure of a Category
- Persisting data successfully
- Deleting records
- Basic queries
- Auto-incrementing integer primary keys
- Summary and outlook
- Chapter 3: Refining the table schema
- More options for the table
- To create is to destroy; to alter is to preserve
- Investigating the impact of our alterations
- Summary and outlook
- Chapter 4: Introducing constraints
- Constraints with SQLite
- Considering database portability
- Changesets: intended changes to data
- Changesets and validation rules
- Turning validation errors into helpful messages
- Summary and outlook
- Chapter 5: Changesets in modules with schemas
- Custom validation functions
- More than one changeset function
- Creating another migration
- Conditionally persisting data in the repo
- Summary and outlook
- Chapter 6: Uniqueness constraints
- Unique indices and unique constraints
- New insights about Ecto and SQLite3
- Ecto migration rollbacks
- Summary and outlook
- Chapter 7: Basic table associations
- Fields with numbers
- A one-to-many association using a foreign key
- Dealing with SQLite’s limitations on foreign key constraints
- A custom validation function for a foreign key constraint
- Summary and outlook
- Chapter 8: Associations with Ecto.Schema
- Interlude: exploration vs. exploitation
- The N+1 query problem vs. Ecto’s
preload/3
- One-to-many relationships and
has_many
- Creating the flip-side of a one-to-many relationship
- Improving upon an existing association
- Summary and outlook
- Chapter 9: Casting and putting associations
- Casting an associated field (unsuccessfully)
- Putting an association
- Creating a new record using
cast_assoc/4
- Casting the reverse association
- Summary and oulook
- Chapter 10: Importing data from a dynamic repository
- Using a dynamic Ecto repo
- Implementing a data importer module
- Importing data in bulk
- Validating that our data importing is robust
- Summary and conclusion
- Chapter 11: Modeling further tables, and data cleansing
- SIPOC of the task of modeling a table
- Data cleansing: dealing with phone numbers
- Importing data from an online CSV data source
- Extracting country names and dial codes
- Creating the Countries table
- Finalizing our automatic generation of the
Countriestable
- Converting phone numbers to the international format
- Creating a validation function for phone numbers
- Tearing down the database and re-importing data
- Modeling the
CustomersandOrderstables
- Defining the new
Ordermodule
- The cherry on top: country name validation
- Reaping the rewards: enabling the
has_manycalls
- Summary and outlook
- Chapter 12: Modeling a join table
- Using
belongs_toandhas_many
- Using
many_to_many
- Summary and outlook
- Using
- Chapter 13: Cleaning up
- Discovering some loose ends
- Tying some loose ends with a table dependency graph
- Implementing a Depth-First Search algorithm
- Restarting from a blank slate
- Summary and outlook
- Chapter 14: Insights from data with queries
- Taking inspiration from a real situation
- Elixir functions vs. database functions
- Simple joins
- The woes of money amounts and floating-point numbers
- Sidequest: rudimentary parallelization using Elixir tasks
- Floating-point values for prices? No, thanks.
- Converting our database to integer prices
- Using a subquery
- Sidequest: customers’ share of revenue, and business resilience
- Left joins: customers without orders
- Dynamic queries
- Virtual fields and fragments
- Top categories and suppliers
- Summary and outlook
- Chapter 15: More and more-advanced queries
- Chapter 16: Bits and pieces: the leftovers
- Chapter 17: Towards “Northwind Elixir Traders 2.0”
- Ideas and exercises
- Summary and outlook
- About the Author
- Before we begin
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