#9 Response Models & Data Shaping

Module 9 — Response Models & Data Shaping

In this module, you will learn:

• Why response models matter

• How to control what data is returned

• How to hide fields

• How to use response_model_exclude_unset, exclude_none, etc.

---

1. Basic Response Model

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class User(BaseModel):
    id: int
    name: str
    email: str

@app.get("/users/{user_id}", response_model=User)
def get_user(user_id: int):
    return {"id": user_id, "name": "John", "email": "john@example.com"}

Now FastAPI ensures:

• Fields are correct

• Types match

• Extra fields are removed

---

2. Response Model That Hides Sensitive Fields

class UserDB(User):
    password: str

@app.get("/user-safe/{user_id}", response_model=User)
def get_safe_user(user_id: int):
    return {"id": user_id, "name": "Ana", "email": "ana@example.com", "password": "secret"}

Even though we returned a password, it will NOT appear.

---

3. Returning Lists

@app.get("/products", response_model=list[User])
def list_users():
    return [
        {"id": 1, "name": "A", "email": "a@example.com"},
        {"id": 2, "name": "B", "email": "b@example.com"}
    ]

---

4. Using response_model_exclude_unset

Useful when you want to hide fields not explicitly set.

@app.get("/partial", response_model=User, response_model_exclude_unset=True)
def partial():
    return {"id": 1}

Output:

{"id":1}

---

5. Excluding or Including Fields

Excluding Fields

@app.get("/exclude", response_model=User, response_model_exclude={"email"})
def exclude_email():
    return {"id": 1, "name": "Test", "email": "hide@example.com"}

Including Only Certain Fields

@app.get("/include", response_model=User, response_model_include={"id", "name"})
def include_name_only():
    return {"id": 1, "name": "Test", "email": "x@example.com"}

---

6. Models With Nested Data

class Address(BaseModel):
    city: str
    country: str

class UserExtended(BaseModel):
    id: int
    name: str
    address: Address

@app.get("/user-details", response_model=UserExtended)
def details():
    return {
        "id": 1,
        "name": "Sam",
        "address": {"city": "Chennai", "country": "India"}
    }

---

🎉 Module 9 Complete!

---

If you want, I can also convert any other module posts to Compose view, or even auto-convert all remaining posts.