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A Rails model is a Ruby class that represents application data and lets your code work with database records through Active Record. To make a first model, generate it with a field, apply the resulting migration to the database, then use the Rails console to create and query records. This walkthrough follows the current Ruby on Rails Getting Started guide; its stated Ruby and Rails requirements apply to that guide’s version, so check the guide for the Rails version installed in your application.
What a Rails model does
Rails is a Ruby web framework organized around the model-view-controller (MVC) pattern. The model is the Ruby-facing data layer: it represents the application’s data and provides a way to work with that data in the database. Rails’ Active Record component maps relational database structures to Ruby code, so application code can work with model instances instead of manually writing SQL for every basic operation.
In the official Getting Started tutorial, SQLite is the default database for the tutorial application. Your application may use a different database, but the model-and-migration workflow remains the central idea: the model describes how Rails works with records, while the database stores them.
Check the guide version before you start
The current official Getting Started guide specifies Ruby 3.2 or newer and Rails 8.1.0 or newer for its example. Those are requirements for that guide, not a timeless requirement for every Rails application. Use the Rails guide matching the version installed in your project, since commands, defaults, and prerequisites can change.
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Generate a model with a field
From your Rails application’s root directory, run the guide’s example command:
bin/rails generate model Product name:stringThis asks Rails to create a Product model with a name field whose database type is a string. The generator creates the model class, a timestamped migration under db/migrate, and model test and fixture files in the guide’s example.
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Understand the generated files
app/models/product.rbcontains the Ruby model class.- A timestamped file in
db/migratedescribes the database structure change for the new model field. - Generated test and fixture files provide places to add model tests and sample test data.
Rails follows a naming convention: the Ruby class is singular, Product, while its database table is plural, products. The name field becomes a column in that table. Rails maps the model to its table by convention, and the column-backed attribute is available on model instances without separately declaring a Ruby attribute for it.
Apply the migration to update the database
A migration is a versioned description of a database structure change. Generating a model creates the migration file, but it does not by itself update the database. Apply the change from the application root:
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bin/rails db:migrateAfter the command runs successfully, the database has the structure described by the migration, including the products table and its name column. The Getting Started guide also demonstrates bin/rails db:rollback to undo the last migration in its example. Treat rollback as a database change, not as a harmless file cleanup: review what the migration changes and the effect on data before using it.
Explore the model in the Rails console
The generated model inherits from ApplicationRecord, which provides the Active Record behavior shared by application models. Start an interactive console in the application root:
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bin/rails consoleAt the console prompt, create and save a product, then query the model:
product = Product.new(name: "Example product")
product.save
Product.allProduct.new builds an in-memory model instance. save attempts to write it to the database, and Product.all asks Active Record for all product records. Active Record translates the query into SQL and returns model instances, so the result is Ruby objects representing database rows.
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Require valid data with a model validation
To prevent products without a name from being saved through the model, add a presence validation to app/models/product.rb:
class Product < ApplicationRecord
validates :name, presence: true
endRails runs validations during save, create, and update operations. If the record is invalid, a save attempt returns false rather than saving it. Inspect the validation details on that instance:
product = Product.new
product.save
product.errors.full_messagesThe errors object holds validation errors, and errors.full_messages returns readable messages that can be shown to a user or used while debugging.
Add associations when the data has a real relationship
Once a single model is clear, associations let model classes express relationships between records. The guide’s example puts has_many :subscribers on Product to represent a product with multiple subscribers:
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has_many :subscribers, dependent: :destroyThe dependent: :destroy option has an important consequence: when a product is destroyed through Active Record, Rails also destroys its associated subscriber records. Use that option only when deleting those associated records is the intended behavior for your application. Associations describe domain relationships; add them when the relationship is part of the data your app needs to represent.
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