مخطط Ecto وترحيلات قاعدة البيانات

Welcome to Ecto! It's Elixir's powerful toolkit for interacting with databases. Think of it as your bridge between Elixir data and your database.

Ecto isn't a traditional Object-Relational Mapper (ORM). Instead, it's a data mapper. This means it focuses on mapping data between your Elixir application (using structs) and your database tables, giving you more control and less 'magic'.

Before Ecto maps data to a database, Elixir uses structs to define data shapes. A struct is a special kind of map that ensures a predefined set of keys and default values.

Ecto schemas build upon this idea, extending structs to understand how their fields correspond to database columns.

Try running this simple struct example:

An Ecto schema is an Elixir module that describes how an Elixir struct maps to a database table. It defines the fields, their types, and any special options.

Here's how you'd define a basic User schema, mapping to a users table in your database:

When defining fields in your schema, you specify their type. Ecto provides many common types that map directly to database types:

• :string: For text data (e.g., names, emails).
• :integer: For whole numbers.
• :float or :decimal: For numbers with decimal points.
• :boolean: For true/false values.
• :datetime or :naive_datetime: For date and time values.
• :binary: For raw binary data.

Choosing the right type helps Ecto validate data and create appropriate database columns.

Ecto schemas automatically include a primary key, usually an id column of type :integer. You don't need to define it explicitly.

The timestamps() macro is super handy! It automatically adds two fields to your schema and database table:

• :inserted_at: Stores when the record was created.
• :updated_at: Stores when the record was last modified.

These fields are crucial for tracking changes and are automatically managed by Ecto.

Your Ecto schemas define the *desired* structure of your database. But how do you apply these changes to the actual database?

This is where migrations come in! A migration is an Elixir script that describes changes to your database schema, like creating tables, adding columns, or changing types. They ensure your database schema evolves in a controlled, versioned way.

You create new migration files using the Mix command mix ecto.gen.migration. You provide a descriptive name for the migration:

This command will generate a new Elixir file in your priv/repo/migrations directory. The filename will include a timestamp, ensuring migrations are applied in the correct order.

A migration file contains an Elixir module with a change/0 function. Inside this function, you define your database operations. For example, creating a table:

Once you've defined your migrations, you apply them to your database using another Mix command:

Ecto keeps track of which migrations have been run. If you need to undo the last migration, you can use mix ecto.rollback.

Always run migrations in your development environment first to catch any issues!

Let's check your understanding of Ecto schemas and migrations.

You've taken the first step into Ecto!

• We learned that Ecto schemas define how Elixir structs map to database tables, specifying fields and types.
• We explored how migrations are versioned scripts that apply these schema changes to your actual database.
• You now know how to define a basic schema, generate migration files, and apply them using Mix commands.

Next, we'll dive deeper into interacting with your database using Ecto.Repo and ensuring data integrity with Changesets.