```python
from typing import List
from fastapi import APIRouter, Depends, HTTPException
from sqlalchemy.orm import Session

from app.db import get_db
from app.models import Comment
from app.schemas import CommentCreate, CommentResponse

router = APIRouter(
    prefix="/comments",
    tags=["Comments"],
)

@router.post("/", response_model=CommentResponse, status_code=201)
def create_comment(comment: CommentCreate, db: Session = Depends(get_db)):
    db_comment = Comment(**comment.dict())
    db.add(db_comment)
    db.commit()
    db.refresh(db_comment)
    return db_comment

@router.get("/", response_model=List[CommentResponse])
def get_all_comments(db: Session = Depends(get_db)):
    comments = db.query(Comment).all()
    return comments

@router.get("/{comment_id}", response_model=CommentResponse)
def get_comment(comment_id: int, db: Session = Depends(get_db)):
    comment = db.query(Comment).filter(Comment.id == comment_id).first()
    if not comment:
        raise HTTPException(status_code=404, detail="Comment not found")
    return comment

@router.put("/{comment_id}", response_model=CommentResponse)
def update_comment(comment_id: int, comment: CommentCreate, db: Session = Depends(get_db)):
    db_comment = db.query(Comment).filter(Comment.id == comment_id).first()
    if not db_comment:
        raise HTTPException(status_code=404, detail="Comment not found")
    for field, value in comment.dict().items():
        setattr(db_comment, field, value)
    db.commit()
    db.refresh(db_comment)
    return db_comment

@router.delete("/{comment_id}", status_code=204)
def delete_comment(comment_id: int, db: Session = Depends(get_db)):
    comment = db.query(Comment).filter(Comment.id == comment_id).first()
    if not comment:
        raise HTTPException(status_code=404, detail="Comment not found")
    db.delete(comment)
    db.commit()
    return None
```


- `POST /comments/`: Create a new comment
- `GET /comments/`: Get all comments
- `GET /comments/{comment_id}`: Get a single comment
- `PUT /comments/{comment_id}`: Update a comment
- `DELETE /comments/{comment_id}`: Delete a comment

The endpoints use SQLAlchemy models and Pydantic schemas for data validation and serialization. The `get_db` dependency is used to get a database session.

Note: Make sure you have the appropriate models and schemas defined in your project, and that the `get_db` function is correctly configured to connect to your database.