Validation in APIs (Ruby on Rails)

Giulliano Bueno
3 min readNov 20, 2023

Validation is a critical aspect of building robust APIs, ensuring that the data received by your application is accurate, secure, and complies with the necessary criteria. In the realm of Ruby on Rails API development, implementing controller action validation is a fundamental step to maintain data integrity. In this blog post, we’ll explore various approaches to implementing validation in Rails API controllers.

Strong Parameters

Rails API controllers can leverage Strong Parameters to protect against mass assignment vulnerabilities. By whitelisting parameters in the controller, you explicitly specify which parameters are allowed for mass assignment, preventing unintended or malicious updates to your models.

class UsersController < ApplicationController
def create
@user = User.new(user_params)
if @user.save
# ...
else
# ...
end
end

private

def user_params
params.require(:user).permit(:name, :email, :password)
end
end

Model Validations

Model validations play a crucial role in API development, allowing you to ensure the integrity of data before it reaches the database. By specifying these validations in your model classes, you can enforce data constraints at the API endpoint level.

class User < ApplicationRecord
validates :name, presence: true
validates :email, presence: true, uniqueness: true
validates :password, presence: true, length: { minimum: 6 }
end

Before Filters

Before filters in Rails API controllers allow you to execute specific actions before the main API action is invoked. This is valuable for performing validation checks, authentication, or other pre-processing steps tailored to your API requirements.

class UsersController < ApplicationController
before_action :find_user, only: [:show, :edit, :update, :destroy]
before_action :validate_params, only: :create

def index
@users = User.all
# Your index action logic here
end

def show
# Your show action logic here
end

def new
@user = User.new
# Your new action logic here
end

def create
@user = User.new(user_params)
if @user.save
# Successful save logic
else
# Handle validation errors
end
end

def edit
# Your edit action logic here
end

def update
if @user.update(user_params)
# Successful update logic
else
# Handle validation errors
end
end

def destroy
@user.destroy
# Your destroy action logic here
end

private

def find_user
@user = User.find(params[:id])
end

def validate_params
render json: { error: 'Invalid parameters' }, status: :unprocessable_entity unless params[:user].present?
end

def user_params
params.require(:user).permit(:name, :email)
end
end

Custom Validation Methods

For intricate validation logic specific to an API endpoint, custom validation methods can be created and called as needed.

class UsersController < ApplicationController
def create
if custom_validation
@user = User.new(user_params)
if @user.save
# ...
else
# ...
end
else
# Handle invalid input
end
end

private

def custom_validation
# Custom validation logic
end
end

In the custom_validation logic, you can either use a simple validation logic that does not make sense to be in the Model class because it is too specific for a scenario strongly connected to the action being executed (create, update, delete, etc.). If you have a complex validation, you should consider creating a Validation service class that will execute all the logic you need to handle that specific case.

In conclusion, these approaches offer a robust strategy for implementing controller action validation in Rails API development. Whether utilizing Strong Parameters, model validations, before filters, or custom methods, selecting the approach aligned with your API’s requirements ensures a secure and reliable data flow.

Stay informed about updates by referring to the official Rails API documentation and guides.

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