🚀 Comprehensive Guide: How to Prepare for a Django Job Interview – 400 Most Common Interview Questions

Are you ready to get a job: https://hackmd.io/@husseinsheikho/django-mcq

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# Django ORM Comparison - Know both frameworks
# Django model (contrast with SQLAlchemy)
from django.db import models

class Department(models.Model):
    name = models.CharField(max_length=50)

class Employee(models.Model):
    name = models.CharField(max_length=100)
    email = models.EmailField(unique=True)
    department = models.ForeignKey(Department, on_delete=models.CASCADE)

# Django query (similar but different syntax)
Employee.objects.filter(department__name="HR").select_related('department')

# Async ORM - Modern Python requirement
# Requires SQLAlchemy 1.4+ and asyncpg
from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession

async_engine = create_async_engine(
    "postgresql+asyncpg://user:pass@localhost/db",
    echo=True,
)
async_session = AsyncSession(async_engine)

async with async_session.begin():
    result = await async_session.execute(
        select(Employee).where(Employee.name == "Alice")
    )
    employee = result.scalar_one()

# Testing Strategies - Interview differentiator
from unittest import mock

# Mock database for unit tests
with mock.patch('sqlalchemy.create_engine') as mock_engine:
    mock_conn = mock.MagicMock()
    mock_engine.return_value.connect.return_value = mock_conn
    
    # Test your ORM-dependent code
    create_employee("Test", "test@company.com")
    mock_conn.execute.assert_called()

# Production Monitoring - Track slow queries
from sqlalchemy import event

@event.listens_for(engine, "before_cursor_execute")
def before_cursor(conn, cursor, statement, params, context, executemany):
    conn.info.setdefault('query_start_time', []).append(time.time())

@event.listens_for(engine, "after_cursor_execute")
def after_cursor(conn, cursor, statement, params, context, executemany):
    total = time.time() - conn.info['query_start_time'].pop(-1)
    if total > 0.1:  # Log slow queries
        print(f"SLOW QUERY ({total:.2f}s): {statement}")

# Interview Power Move: Implement caching layer
from functools import lru_cache

class CachedEmployeeRepository(EmployeeRepository):
    @lru_cache(maxsize=100)
    def get_by_id(self, employee_id):
        return super().get_by_id(employee_id)
    
    def invalidate_cache(self, employee_id):
        self.get_by_id.cache_clear()

# Reduces database hits by 70% in read-heavy applications

# Pro Tip: Schema versioning in CI/CD pipelines
# Sample .gitlab-ci.yml snippet
deploy_db:
  stage: deploy
  script:
    - alembic upgrade head
    - pytest tests/db_tests.py  # Verify schema compatibility
  only:
    - main

# Real-World Case Study: E-commerce inventory system
class Product(Base):
    __tablename__ = 'products'
    id = Column(Integer, primary_key=True)
    sku = Column(String(20), unique=True)
    stock = Column(Integer, default=0)
    
    # Atomic stock update (prevents race conditions)
    def decrement_stock(self, quantity, session):
        result = session.query(Product).filter(
            Product.id == self.id,
            Product.stock >= quantity
        ).update({"stock": Product.stock - quantity})
        if not result:
            raise ValueError("Insufficient stock")

# Usage during checkout
product.decrement_stock(2, session)

By: @DATASCIENCE4 🔒

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@app.post("/uploadfile/")
async def create_upload_file(file: UploadFile = File(...)):
    return {"filename": file.filename, "content_type": file.content_type}

• Set a response cookie.

from fastapi import Response
@app.post("/cookie/")
def create_cookie(response: Response):
    response.set_cookie(key="fakesession", value="fake-cookie-session-value")
    return {"message": "Cookie set"}

• Read a request cookie.

from fastapi import Cookie
@app.get("/read-cookie/")
def read_cookie(fakesession: Optional[str] = Cookie(None)):
    return {"session": fakesession}

X. Error Handling & Advanced Responses

• Handle HTTPException.

from fastapi import HTTPException
@app.get("/items/{item_id}")
def read_item(item_id: str):
    if item_id not in items_db:
        raise HTTPException(status_code=404, detail="Item not found")

• Return a custom JSONResponse.

from fastapi.responses import JSONResponse
@app.get("/custom/")
def custom_response():
    return JSONResponse(status_code=202, content={"message": "Accepted"})

• Return an HTMLResponse.

from fastapi.responses import HTMLResponse
@app.get("/page", response_class=HTMLResponse)
def read_page():
    return "<h1>Hello World</h1>"

• Define a WebSocket endpoint.

from fastapi import WebSocket
@app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket):
    await websocket.accept()
    await websocket.send_text("Hello from WebSocket")
    await websocket.close()

• Handle a path operation that may not exist.

@app.get("/{full_path:path}")
def read_catch_all(full_path: str):
    return {"path": full_path}

• Mount a static files directory.

from fastapi.staticfiles import StaticFiles
app.mount("/static", StaticFiles(directory="static"), name="static")

• Add a custom exception handler.

from fastapi import Request
from fastapi.responses import JSONResponse

class MyCustomException(Exception): pass

@app.exception_handler(MyCustomException)
async def custom_exception_handler(request: Request, exc: MyCustomException):
    return JSONResponse(status_code=418, content={"message": "I'm a teapot"})

• Read a request header.

from fastapi import Header
@app.get("/headers/")
async def read_headers(user_agent: Optional[str] = Header(None)):
    return {"User-Agent": user_agent}

• Get a raw Request object.

from fastapi import Request
@app.get("/request-info")
def get_request_info(request: Request):
    return {"client_host": request.client.host}

#Python #FastAPI #API #WebDevelopment #Pydantic

━━━━━━━━━━━━━━━
By: @DataScience4 ✨

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