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Wave 6: Establishing a One-to-Many Relationship

Goal

Our users want to associate Tasks and Goals. Specifically, our users want to designate that there are many tasks that serve one goal.

This wave focuses on creating a one-to-many relationship between goals and tasks, where a goal has-many tasks, and a task belongs to one goal.

When we have many tasks and many goals, users will want to conveniently gather all of the tasks associated with one goal. Our API should serve this information with a new route, /goals/<goal_id>/tasks.

Requirements

We should:

  1. Update our models so that the relationship between them is created in our database.
  2. Create our new route, /goals/<goal_id>/tasks, so that our API gives back the right information.

Use the tests in tests/test_wave_06.py to guide your implementation.

  • Some tests use a fixture named one_task_belongs_to_one_goal that is defined in tests/conftest.py.
    • This fixture uses other fixtures to save a task and a goal to the test database, then associates the task with the goal, and stores that updated relationship in the test database.

Tips

  • Use lesson materials and independent research to review how to set up a one-to-many relationship in Flask.
  • Remember to run flask db migrate and flask db upgrade whenever there is a change to a model.
  • Pay attention to the exact shape of the expected JSON. Double-check nested data structures and the names of the keys for any misspellings.

Updates to the Goal Model

The Goal model should have a relationship with the model Task.

After reviewing the strategy for creating a one-to-many relationship, it is up to you if you would like to add convenience attributes for accessing the Goal model from it's related Tasks and vice versa, accessing the list of associated Tasks from a Goal model.

Updates to the Task Model

The Task model should belong to one Goal.

After reviewing the strategy for creating a one-to-many relationship, in the Task model, we recommend:

  • Setting the foreign key to goal's primary key column
  • Using Optional syntax to make the attribute nullable

Sending a List of Task IDs to a Goal

Given:

  • a goal that has the ID 1
  • three tasks with the IDs 1, 2, and 3

When I send a POST request to /goals/1/tasks with this request body:

{
  "task_ids": [1, 2, 3]
}

Then the three Tasks belong to the Goal and it gets updated in the database. We get back a 200 OK with the following response body:

{
  "id": 1,
  "task_ids": [1, 2, 3]
}

We will need to validate that the Goal ID, as well as each Task ID exists in the database. A route helper method that can resolve a model instance from its ID would help us validate the IDs in the request body.

Getting Tasks of One Goal

Given a goal that has:

  • An id 333
  • A title attribute with the value "Build a habit of going outside daily"

and a task that has:

  • An id 999
  • A title attribute with the value "Go on my daily walk 🏞"
  • A description attribute with the value "Notice something new every day"
  • A completed_at attribute with a null value
  • It belongs to the Goal with ID 333

when I send a GET request to /goals/333/tasks,

then I get this response:

200 OK

{
  "id": 333,
  "title": "Build a habit of going outside daily",
  "tasks": [
    {
      "id": 999,
      "goal_id": 333,
      "title": "Go on my daily walk 🏞",
      "description": "Notice something new every day",
      "is_complete": false
    }
  ]
}

Notice that if we have been using a model helper method to return a dictionary representation of a Task, we can use this method to help build this route response.

This is also true of the Goal model helper method. We may need to introduce logic to allow it to work in this context, or use the existing method to generate the basic dictionary representation of the Goal and then add the additional data for the associated Task models.

Getting Tasks of One Goal: No Matching Tasks

Given a goal that has:

  • An id 333
  • A title attribute with the value "Build a habit of going outside daily"

and no tasks that belong to this goal,

when I send a GET request to /goals/333/tasks,

then I get this response:

200 OK

{
  "id": 333,
  "title": "Build a habit of going outside daily",
  "tasks": []
}

Getting Tasks of One Goal: No Matching Goal

Given that no goals exist,

when I send a GET request to /goals/1/tasks,

then I get this response:

404 Not Found

You may choose the response body.

Make sure to complete the tests for non-existing tasks to check that the correct response body is returned.