Associations and Embedded Schemas

In relational databases, data is often spread across multiple tables to avoid redundancy and ensure data integrity. Associations in Ecto help you define how these different pieces of data relate to each other.

Think of a blog: A user can write many posts, and each post belongs to one user. Ecto allows you to model these relationships directly in your Elixir schemas.

• Organize related data logically.
• Simplify querying and data retrieval.
• Maintain data consistency.

The most common relationship is one-to-many. For example, one User can have many Posts, but each Post belongs to only one User.

In Ecto, you define this using has_many on the "one" side (e.g., User) and belongs_to on the "many" side (e.g., Post). The belongs_to macro also tells Ecto to add a foreign key (like user_id) to the Post's database table.