How to make a field required in Rails?

In Rails, you can make a field required by adding a validation to your model.

Here's an example of how to make the "name" field required in a model named "Product":

class Product < ApplicationRecord
  validates :name, presence: true
end

In this example, the validates method is used to specify a validation for the "name" field. The presence: true option means that the field must have a non-blank value in order for the record to be considered valid.

You can also specify a custom error message for the validation by adding a message option:

class Product < ApplicationRecord
  validates :name, presence: { message: "must be provided" }
end

Now, if a record with a blank "name" field is saved, it will not be valid and the error message "Name must be provided" will be added to the errors collection for the "name" attribute.