Creating and Testing Uniqueness Validations
In this demonstration, I will show how to use the Rails model validation helper, uniqueness, to enforce that the value of a specified model attribute must be unique (i.e., not already assigned to some other record in the database) in order to be saved in the database. We will continue to build upon the QuizMe project from the previous demos.
In particular, we will use the uniqueness validation helper to ensure that the question attribute for each McQuestion object stored in the database is unique. The idea here is that we do not want the same question to appear twice in the database.
1. Adding a uniqueness Validation to the McQuestion Model Class
In the the McQuestion model class, update the validation for the question attribute by inserting a uniqueness validation, like this:
validates :question,
presence: true,
uniqueness: true
Note that we also inserted line breaks and indentation into the validates :question declaration above to enhance its readability.
Verify that we didn’t accidentally introduce a syntax error into the model class by running the valid McQuestion fixture tests, like this:
rails test
If no syntax errors were made, the tests should run with no failures and no errors.
2. Testing the uniqueness Validation in the McQuestion Model Class
Verify that we declared the uniqueness validation correctly by adding a model test to McQuestionTest, like this:
test "question uniqueness not valid" do
one = mc_questions(:one)
two = mc_questions(:two)
one.question = two.question
assert_not one.valid?
end
Note the strategy we used in the above test. We retrieve both fixtures, one and two, from the test database. Then, we assign the question attribute for one to be the same as for two. Because two is already saved in the database, our uniqueness validation should cause one to evaluate as invalid.
Check that the test runs as expected by entering the following command:
rails test
If the uniqueness validation works correctly, the tests should run with no failures and no errors.