Build One API Endpoint

Software Development with Claude Code

Dani Zysman

AI Curriculum Manager @ DataCamp

From Query to API

recraft: half: A developer at a desk with Claude AI assistant helping build an API, showing code on screen with database connection

Previous Video: Queried the database interactively
Now: Add an endpoint to the Music Analytics API
- One prompt, one working endpoint, real Python code

The Project So Far

music-analytics-api/
  app.py             # Existing API (updated to register db_routes)
  routes.py          # Existing routes
  models.py          # Artist/Album models
  db_routes.py       # <- New database-backed Blueprint
  chinook.db
  test_routes.py
  CLAUDE.md

Ask Claude to Build It

> Create a new db_routes.py blueprint with an endpoint at 
/artists/<artist_id>/albums that returns all albums by 
a specific artist as JSON from chinook,db. Register it with @app.py

1. db_routes py - New Flask Blueprint with:
    - get_db_connection() helper to connect to chinook.db
    - Added endpoint that queries the database for all albums by a specific artist
    - Returns JSON with AlbumId, Title, and ArtistId fields
2. Updated app.py 
    - Registered the blueprint so the new endpoint is active

The endpoint will return a 404 if the artist doesn't exist, 
and returns albums sorted by title as JSON.

The Generated Code

@app.route("/artists/<int:artist_id>/albums")
def get_artist_albums(artist_id):
    conn = get_db()
    artist = conn.execute("SELECT ... WHERE ArtistId = ?", ...)
    albums = conn.execute("SELECT ... WHERE ArtistId = ?", ...)
    conn.close()
    return jsonify({"artist": ..., "albums": [...]})

Test It Locally

$ python app.py & PID=$! && sleep 3 && curl http://127.0.0.1:5000/artists/1/albums
&& kill $PID

127.0.0.1 "GET /artists/1/albums HTTP/1.1" 200
[
    {
     "album_id": 1,
     "artist_id": 1,
     "title": "For Those About To Rock We Salute You"
    },
    {
     "album_id": 4,
     "artist_id": 1,
     "title": "Let There Be Rock"
    }
]

Handle Edge Cases

What if...
- Artist ID doesn't exist?
- Artist has no albums?
- Invalid ID format?
- Current code returns empty {"albums": []}

Better responses:
- 404 with clear message
- Validated response structure
- Proper error handling

Add Validation with Pydantic

from pydantic import BaseModel
from typing import List

class Album(BaseModel):
    id: int
    title: str

class ArtistAlbums(BaseModel):
    artist_id: int
    albums: List[Album]

Pydantic provides:
- Type validation
- Automatic serialization
- Clear error messages
- Self-documenting schemas

Ask Claude to Add Validation

> Add Pydantic validation to @db_routes.py. Return 404 with a message if the 
artist doesn't exist or has no albums.

Done! Added Pydantic validation to db_routes.py:
Changes:
- Added Album model (album_id, title, artist_id)
- Returns 404 "Artist not found" if artist doesn't exist
- Returns 404 "Artist has no albums" if artist has no albums
- Validates each album against Album model before returning
- Returns 400 on validation errors
Responses:
- 404 "Artist not found"
- 404 "Artist has no albums"  
- 200 with validated album data

Let's Practice!

Software Development with Claude Code