Breaking Down Task Comments

From Plan to Action

In our previous lessons, we learned how to create a high-level technical plan . This plan acts as our map. Now, we are ready to move from planning to building. Our goal is to add a comments feature to our task management app . This feature allows users to add comments to tasks, see a list of comments, and delete their own comments . If we ask an AI like Codex to "Build the whole comment system," it might get overwhelmed and make mistakes. Instead, we take our technical plan and break it into small, executable steps. This ensures that the code is high-quality and easy to test. In the CodeSignal IDE, you will find that the libraries we use, like SQLAlchemy for databases and Pytest for testing, are already installed. You can focus entirely on the logic of building your feature.

Decomposing the Comments Feature

To build a feature successfully, we group our work into logical phases. We call these atomic tasks . A task is atomic if it focuses on one thing, affects only a few files, and can be finished in one sitting — usually in under 2 hours. For our comments feature, we split the work like this: Phase Task ID Focus Dependencies Foundation T001, T002 database model and repository None Business Logic T003, T004 services and validation schemas T001, T002 API Layer T005, T006 endpoints and authorization T003, T004 Integration T007 Final end-to-end tests All previous By following this order, we ensure that we never build a "roof" (the API) before we have a "foundation" (the database).

Phase	Task ID	Focus	Dependencies
Foundation	`T001`, `T002`	database model and repository	None
Business Logic	`T003`, `T004`	services and validation schemas	`T001`, `T002`
API Layer	`T005`, `T006`	endpoints and authorization	`T003`, `T004`
Integration	`T007`	Final end-to-end tests	All previous

Defining Task Requirements (The Template)

Every task needs a clear set of instructions so that Codex knows exactly what "done" looks like. We use a standard template for this. Let's look at the requirements for our first task, T001 . Task Template: [T001] Create Comment Model Files Modified : src/models/comment.py, tests/unit/test_comment_model.py . acceptance criteria : Model defined as a SQLAlchemy declarative model with proper Python type hints. Fields: id (Integer, primary key), task_id (Integer, Foreign Key), author_id (Integer, Foreign Key), content (String), created_at (DateTime). Relationships: task (to Task model), author (to User model). All foreign key columns explicitly marked as nullable=False . unit tests verify field types, relationships, and timestamp handling. Dependencies : None. Estimated Time : 45 minutes. Notice the checkboxes. These are called acceptance criteria . They act as a checklist for both you and Codex. If every box is not checked, the task is not finished.

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The Test-First Workflow with Codex

When you start a task with Codex, you should use a test-first workflow. This means we ask Codex to write the test before the actual code. This ensures that the code actually does what we want.

Let's walk through how you would prompt Codex for T001.

Step 1: The Initial Prompt You tell Codex: "Create the Comment model following the T001 acceptance criteria. Write the tests first, verify they fail, then implement the model, and verify they pass."

Step 2: Writing the Failing Test Codex will first create a test file. Since the Comment model does not exist yet, the test will fail.

Python

# tests/unit/test_comment_model.py
import pytest
from datetime import datetime
from src.models.comment import Comment

def test_create_comment_with_all_required_fields():
    # This will fail because the Comment model does not exist yet
    comment = Comment(
        content="Great task!",
        task_id=1,
        author_id=1,
    )

    assert comment.content == "Great task!"
    assert comment.task_id == 1
    assert comment.author_id == 1

# tests/unit/test_comment_model.py
import pytest
from datetime import datetime
from src.models.comment import Comment

def test_create_comment_with_all_required_fields():
    # This will fail because the Comment model does not exist yet
    comment = Comment(
        content="Great task!",
        task_id=1,
        author_id=1,
    )

    assert comment.content == "Great task!"
    assert comment.task_id == 1
    assert comment.author_id == 1

When Codex runs this test, the output will look like this:

text

ModuleNotFoundError: No module named 'src.models.comment'
or
ImportError: cannot import name 'Comment' from 'src.models.comment'

ModuleNotFoundError: No module named 'src.models.comment'
or
ImportError: cannot import name 'Comment' from 'src.models.comment'

Step 3: Implementing the Model Now Codex writes the actual code to make the test pass, following the exact patterns used in this project.

Python

# src/models/comment.py
from datetime import datetime, timezone
from sqlalchemy import Column, Integer, String, DateTime, ForeignKey
from sqlalchemy.orm import relationship
from src.database import Base


class Comment(Base):
    __tablename__ = "comments"

    id = Column(Integer, primary_key=True)
    task_id = Column(Integer, ForeignKey("tasks.id"), nullable=False)
    author_id = Column(Integer, ForeignKey("users.id"), nullable=False)
    content = Column(String, nullable=False)
    created_at = Column(
        DateTime, default=lambda: datetime.now(timezone.utc), nullable=False
    )

    # Relationships
    task = relationship("Task", back_populates="comments")
    author = relationship("User")

# src/models/comment.py
from datetime import datetime, timezone
from sqlalchemy import Column, Integer, String, DateTime, ForeignKey
from sqlalchemy.orm import relationship
from src.database import Base


class Comment(Base):
    __tablename__ = "comments"

    id = Column(Integer, primary_key=True)
    task_id = Column(Integer, ForeignKey("tasks.id"), nullable=False)
    author_id = Column(Integer, ForeignKey("users.id"), nullable=False)
    content = Column(String, nullable=False)
    created_at = Column(
        DateTime, default=lambda: datetime.now(timezone.utc), nullable=False
    )

    # Relationships
    task = relationship("Task", back_populates="comments")
    author = relationship("User")

Key Pattern Details:

We use Integer as the primary key type, consistent with the User and Task models already in this project.
We use DateTime for timestamp columns with default=lambda: datetime.now(timezone.utc) to set the creation time automatically.
All foreign key columns are explicitly marked with nullable=False, ensuring data integrity at the database level.
We use String for content to store the comment text.
The column is named author_id (not user_id) to be semantically clear that this field refers to the comment's author.
Relationships use back_populates for bidirectional references — task points back to the Task model's comments relationship, which you can see defined in src/models/task.py.
We follow snake_case naming conventions for both the table name and all column names.

Step 4: Verifying Success Codex runs the test again. This time, it passes!

text

============================= test session starts ==============================
collected 1 item

tests/unit/test_comment_model.py::test_create_comment_with_all_required_fields PASSED

============================== 1 passed in 0.12s ===============================

============================= test session starts ==============================
collected 1 item

tests/unit/test_comment_model.py::test_create_comment_with_all_required_fields PASSED

============================== 1 passed in 0.12s ===============================

Finally, you would commit this work with a clear message: feat(comments): Add Comment model (T001).

From Plan to Action

Decomposing the Comments Feature

Defining Task Requirements (The Template)

Join the 1M+ learners on CodeSignal

The Test-First Workflow with Codex

Recognizing and Recovering from Task Bloat

Summary and Practice Prep