数据库和ORMS：使用SQLAlchemy与数据库通信

文章目录

1. 环境安装
2. 使用SQLAlchemy与SQL数据库通信
- 2.1 创建表
- 2.2 连接数据库
- 2.3 insert、select
- 2.4 update、delete
- 2.5 relationships
- 2.6 用Alembic进行数据库迁移

learn from 《Building Data Science Applications with FastAPI》

1. 环境安装

docker 安装 MongoDB 服务

 docker run -d --name fastapi-mongo -p 27017:27017 mongo:4.4

2. 使用SQLAlchemy与SQL数据库通信

安装 pip install databases[sqlite]

2.1 创建表

# models.pyimport sqlalchemy
from datetime import datetime
from typing import Optional
from pydantic import BaseModel, Fieldmetadata = sqlalchemy.MetaData()  # 创建元数据对象posts = sqlalchemy.Table(  # 创建表对象'posts',  # 表名metadata,  # 元数据对象# 列对象（列名，类型，其他选项）sqlalchemy.Column('id', sqlalchemy.Integer, primary_key=True, autoincrement=True),sqlalchemy.Column('publication_date', sqlalchemy.DateTime(), nullable=False),sqlalchemy.Column('title', sqlalchemy.String(255), nullable=False),sqlalchemy.Column('text', sqlalchemy.Text(), nullable=False),
)class PostBase(BaseModel):title: strtext: strpublication_date: datetime = Field(dafault_factory=datetime.now)class PostPartialUpdate(BaseModel):text: Optional[str] = Nonecontent: Optional[str] = Noneclass PostCreate(PostBase):passclass PostDB(PostBase):id: int

2.2 连接数据库

# _*_ coding: utf-8 _*_
# @Time : 2022/3/8 9:28
# @Author : Michael
# @File : database.py
# @desc :
import sqlalchemy
from databases import Database
DB_URL = 'sqlite:///cp6_sqlalchemy.db'
database = Database(DB_URL)
sqlalchemy_engine = sqlalchemy.create_engine(DB_URL)def get_database() -> Database:return database

2.3 insert、select

# _*_ coding: utf-8 _*_
# @Time : 2022/3/8 9:40
# @Author : Michael
# @File : app.py
# @desc :from typing import List, Tuple
import uvicorn
from databases import Database
from fastapi import Depends, FastAPI, HTTPException, Query, statusfrom database import get_database, sqlalchemy_engine
from models import metadata, posts, PostDB, PostCreate, PostPartialUpdateapp = FastAPI()@app.on_event('startup') # 启动的时候执行数据库连接
async def startup():await get_database().connect()metadata.create_all(sqlalchemy_engine)@app.on_event("shutdown") # 关闭的时候执行数据库断开连接
async def shutdown():await get_database().disconnect()async def pagination(skip: int = Query(0, ge=0),limit: int = Query(10, ge=0),) -> Tuple[int, int]:capped_limit = min(100, limit)return (skip, capped_limit)async def get_post_or_404(id: int, database: Database = Depends(get_database)) -> PostDB:select_query = posts.select().where(posts.c.id == id)raw_post = await database.fetch_one(select_query)if raw_post is None:raise HTTPException(status_code=status.HTTP_404_NOT_FOUND)return PostDB(**raw_post)# 开始插入数据
@app.post("/posts/", response_model=PostDB, status_code=status.HTTP_201_CREATED)
async def create_post(post: PostCreate, db: Database = Depends(get_database)) -> PostDB:# 创建插入语句，不必手写sqlinsert_query = posts.insert().values(post.dict())# 执行插入语句命令post_id = await db.execute(insert_query)post_db = await get_post_or_404(post_id, db)return post_db@app.get("/posts/{id}", response_model=PostDB)
async def get_post(post: PostDB = Depends(get_post_or_404)) -> PostDB:return post@app.get("/posts")
async def list_posts(pagination: Tuple[int, int] = Depends(pagination),database: Database = Depends(get_database),) -> List[PostDB]:skip, limit = paginationselect_query = posts.select().offset(skip).limit(limit)rows = await database.fetch_all(select_query)results = [PostDB(**row) for row in rows]return resultsif __name__ == '__main__':uvicorn.run(app='app:app', host="127.0.0.1", port=8001, reload=True, debug=True)

2.4 update、delete

# update
@app.patch("/posts/{id}", response_model=PostDB)
async def update_post(post_update: PostPartialUpdate,post: PostDB = Depends(get_post_or_404),database: Database = Depends(get_database)) -> PostDB:update_query = (posts.update().where(posts.c.id == post.id).values(post_update.dict(exclude_unset=True)))await database.execute(update_query)post_db = await get_post_or_404(post.id, database)return post_db

# delete
@app.delete("/posts/{id}",status_code=status.HTTP_204_NO_CONTENT)
async def delete_post(post: PostDB = Depends(get_post_or_404),database: Database = Depends(get_database)) -> None:delete_query = posts.delete().where(posts.c.id == post.id)await database.execute(delete_query)

2.5 relationships

models.py 编写新的表

comments = sqlalchemy.Table("comments",metadata,sqlalchemy.Column("id", sqlalchemy.Integer, primary_key=True, autoincrement=True),# 定义连接的外键sqlalchemy.Column("post_id", sqlalchemy.ForeignKey("posts.id", ondelete="CASCADE"), nullable=False),sqlalchemy.Column("publication_date", sqlalchemy.DateTime(), nullable=False),sqlalchemy.Column("content", sqlalchemy.Text(), nullable=False),
)class CommentBase(BaseModel):post_id: intpublication_date: datetime = Field(default_factory=datetime.now)content: strclass CommentCreate(CommentBase):passclass CommentDB(CommentBase):id: int

app.py 添加内容

from typing import List, Mapping, Tuple, cast
from models import metadata, posts, PostDB, PostCreate, PostPartialUpdate, comments, CommentCreate, CommentDB@app.post("/comments", response_model=CommentDB, status_code=status.HTTP_201_CREATED)
async def create_comment(comment: CommentCreate, database: Database = Depends(get_database)
) -> CommentDB:# 选取post表单数据select_post_query = posts.select().where(posts.c.id == comment.post_id)post = await database.fetch_one(select_post_query)if post is None:raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=f"Post {id} does not exist")# 插入comment 语句insert_query = comments.insert().values(comment.dict())comment_id = await database.execute(insert_query)# 查询 commentselect_query = comments.select().where(comments.c.id == comment_id)raw_comment = cast(Mapping, await database.fetch_one(select_query))return CommentDB(**raw_comment)

获取一个post的全部comments

models.py

class PostPublic(PostDB):comments: Optional[List[CommentDB]] = None

app.py

# _*_ coding: utf-8 _*_
# @Time : 2022/3/8 9:40
# @Author : Michael
# @File : app.py
# @desc :from typing import List, Mapping, Tuple, cast
import uvicorn
from databases import Database
from fastapi import Depends, FastAPI, HTTPException, Query, statusfrom database import get_database, sqlalchemy_engine
from models import metadata, posts, PostDB, PostCreate, PostPartialUpdate, comments, CommentCreate, CommentDB, \PostPublicapp = FastAPI()@app.on_event('startup')  # 启动的时候执行数据库连接
async def startup():await get_database().connect()metadata.create_all(sqlalchemy_engine)@app.on_event("shutdown")  # 关闭的时候执行数据库断开连接
async def shutdown():await get_database().disconnect()async def pagination(skip: int = Query(0, ge=0),limit: int = Query(10, ge=0), ) -> Tuple[int, int]:capped_limit = min(100, limit)return (skip, capped_limit)async def get_post_or_404(id: int, database: Database = Depends(get_database)) -> PostPublic:select_query = posts.select().where(posts.c.id == id)raw_post = await database.fetch_one(select_query)if raw_post is None:raise HTTPException(status_code=status.HTTP_404_NOT_FOUND)# 编号为id的post的所有commentsselect_post_comment_query = comments.select().where(comments.c.post_id == id)raw_comments = await database.fetch_all(select_post_comment_query)comments_list = [CommentDB(**row) for row in raw_comments]return PostPublic(**raw_post, comments=comments_list)# 开始插入数据
@app.post("/posts", response_model=PostDB, status_code=status.HTTP_201_CREATED)
async def create_post(post: PostCreate, db: Database = Depends(get_database)) -> PostPublic:# 创建插入语句，不必手写sqlinsert_query = posts.insert().values(post.dict())# 执行插入语句命令post_id = await db.execute(insert_query)post_db = await get_post_or_404(post_id, db)return post_db@app.get("/posts")
async def list_posts(pagination: Tuple[int, int] = Depends(pagination),database: Database = Depends(get_database), ) -> List[PostDB]:skip, limit = paginationselect_query = posts.select().offset(skip).limit(limit)rows = await database.fetch_all(select_query)results = [PostDB(**row) for row in rows]return results@app.get("/posts/{id}", response_model=PostPublic)
async def get_post(post: PostPublic = Depends(get_post_or_404)) -> PostPublic:return post@app.get("/posts")
async def list_posts(pagination: Tuple[int, int] = Depends(pagination),database: Database = Depends(get_database), ) -> List[PostDB]:skip, limit = paginationselect_query = posts.select().offset(skip).limit(limit)rows = await database.fetch_all(select_query)results = [PostDB(**row) for row in rows]return results# update
@app.patch("/posts/{id}", response_model=PostPublic)
async def update_post(post_update: PostPartialUpdate,post: PostPublic = Depends(get_post_or_404),database: Database = Depends(get_database)) -> PostPublic:update_query = (posts.update().where(posts.c.id == post.id).values(post_update.dict(exclude_unset=True)))await database.execute(update_query)post_db = await get_post_or_404(post.id, database)return post_db# delete
@app.delete("/posts/{id}", status_code=status.HTTP_204_NO_CONTENT)
async def delete_post(post: PostPublic = Depends(get_post_or_404),database: Database = Depends(get_database)) -> None:delete_query = posts.delete().where(posts.c.id == post.id)await database.execute(delete_query)@app.post("/comments", response_model=CommentDB, status_code=status.HTTP_201_CREATED)
async def create_comment(comment: CommentCreate, database: Database = Depends(get_database)
) -> CommentDB:select_post_query = posts.select().where(posts.c.id == comment.post_id)post = await database.fetch_one(select_post_query)if post is None:raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=f"Post {comment.post_id} does not exist")insert_query = comments.insert().values(comment.dict())comment_id = await database.execute(insert_query)select_query = comments.select().where(comments.c.id == comment_id)raw_comment = cast(Mapping, await database.fetch_one(select_query))return CommentDB(**raw_comment)if __name__ == '__main__':uvicorn.run(app='app:app', host="127.0.0.1", port=8001, reload=True, debug=True)

2.6 用Alembic进行数据库迁移

pip install alembic

终端输入：

alembic init alembic

初始化迁移环境，其中包括一组文件和目录，Alembic将在其中存储其配置和迁移文件，需要一起提交 git

在 env.py 中导入元数据

from web_python_dev.sqlalchemy1.models import metadatatarget_metadata = metadata

编辑ini配置

开始迁移

alembic revision --autogenerate -m "Initial migration"

之后会生成一个py文件

该代码内有两个函数：upgrade，downgrade用于数据迁移和回滚

# 升级
alembic upgrade head

数据的迁移和升级之前请做好备份和测试，防止丢失损坏
https://alembic.sqlalchemy.org/en/latest/index.html

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