Technology Sharing

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Previously, we shared the operation of database tables based on a single table. When we designed the database, we also designed cross-table operations. Let's take a look at the design of the database.

class User(Base):
    __tablename__ = "users"
 
    id = Column(Integer, primary_key=True, index=True)
    email = Column(String(10), unique=True, index=True)
    hashed_password = Column(String(100))
    is_active = Column(Boolean, default=True)
    items = relationship("Item", back_populates="owner")
 
 
class Item(Base):
    __tablename__ = "items"
 
    id = Column(Integer, primary_key=True, index=True)
    title = Column(String(10), index=True)
    description = Column(String(10), index=True)
    owner_id = Column(Integer, ForeignKey("users.id"))
    owner = relationship("User", back_populates="items")

Next, let's look at the complete code

from typing import Optional, List
 
"""
数据库多表操作
"""
 
from sqlalchemy import create_engine, ForeignKey
from sqlalchemy.orm import declarative_base
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy import Column, Integer, String, Boolean
 
conn = "mysql+pymysql://{username}:{password}@{host}:{port}/{database}?charset=utf8".format(
    username="root", password="123456", host="10.30.10.36", port=3306, database="fastapi_learn_road")
engine = create_engine(conn)
 
# 该类的每个实例都是一个数据库会话，该类本身还不是数据库会话，但是一旦我们创建了SessionLocal的实例，这个实例将是实际的数据库会话
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
 
# 创建数据库基类
Base = declarative_base()
 
 
# 创建两个数据库模型，继承自Base基类
class User(Base):
    __tablename__ = "users"
 
    id = Column(Integer, primary_key=True, index=True)
    email = Column(String(10), unique=True, index=True)
    hashed_password = Column(String(100))
    is_active = Column(Boolean, default=True)
    items = relationship("Item", back_populates="owner")
 
 
class Item(Base):
    __tablename__ = "items"
 
    id = Column(Integer, primary_key=True, index=True)
    title = Column(String(10), index=True)
    description = Column(String(10), index=True)
    owner_id = Column(Integer, ForeignKey("users.id"))
    owner = relationship("User", back_populates="items")
 
 
from pydantic import BaseModel
from sqlalchemy.orm import Session
from fastapi import FastAPI, Depends, HTTPException
 
 
def create_db():
    """每个请求处理完毕后关闭当前连接，不同的请求使用不同的链接"""
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()
 
 
app = FastAPI()
 
 
# -------------------------以下是多表操作
class BaseItem(BaseModel):
    title: str
    description: Optional[str] = None
 
 
class ItemModel(BaseItem):
    pass
 
 
class ItemOut(BaseItem):
    id: int
    owner_id: int
 
    class Config:
        orm_mode = True
 
 
@app.post("/items/{uid}", response_model=ItemOut)
def create_item_by_user(uid: int, item: ItemModel, db: Session = Depends(create_db)):
    init_item = Item(**item.dict(), owner_id=uid)
    db.add(init_item)
    db.commit()
    db.refresh(init_item)
    return init_item
 
 
# 分页获取所有的items
@app.get("/items", response_model=List[ItemOut])
def get_items(skip: int = 0, limit: int = 10, db: Session = Depends(create_db)):
    return db.query(Item).offset(skip).limit(limit).all()
 
 
# 如何查询用户的items
@app.get("/items/{uid}", response_model=List[ItemOut])
def get_items_by_uid(uid: int, db: Session = Depends(create_db)):
    user = db.query(User).filter(User.id==uid).first()
    if not user:
        raise HTTPException(status_code=200, detail="this user is not valid")
    return db.query(Item).filter(Item.owner==user).offset(0).limit(2).all()

Postman requests to create an item

Query all items

Query the items of a specified user

We have implemented a simple multi-table query.