为什么 sqlllachemy 返回类而不是字符串

Question

因此，作为学习 sql alchemy 的一部分，我正在查询 chinook 数据库，遵循文档和我的课程结构，我相信我已经设置了查询表的正确格式。

### --- USING SQL ALCHEMY TO QUERY DATABASES --- ###

### --- IMPORT --- ###
from sqlalchemy import (
    create_engine, Table, Column, Float, ForeignKey, Integer, String, MetaData
)

### --- SETUP DB --- ###

# executing the instructions from our localhost "chinook" db
#(3/// means hosted locally)
db = create_engine("postgresql:///chinook")

# save a collection about our table objects and the data inside them
meta = MetaData(db)

### --- QUERY --- ###

#1. create variable for table we want to utilize
#(we feed in the subheadings we want, artist, id, name)
artist_table = Table(
    "Artist", meta,
    Column("ArtistId", Integer, primary_key=True),
    Column("Name", String)
)

#variable for album other tables would be made in the same way
album_table = Table(
    "Album", meta,
    Column("AlbumId", Integer, primary_key=True),
    Column("Title", String),
    Column("ArtistId", Integer, ForeignKey("artist_table.ArtistId"))
)
#seeing as artist id is a key that's linked from artist this is a foreign key for this table
#pretty much we want to set the table and column to point to

track_table = Table(
    "Track", meta,
    Column("TrackId", Integer, primary_key=True),
    Column("Name", String),
    Column("AlbumId", Integer, ForeignKey("album_table.AlbumId")),
    Column("MediaTypeId", Integer, primary_key=False),
    Column("GenreId", Integer, primary_key=False),
    Column("Composer", String),
    Column("Milliseconds", Integer),
    Column("Bytes", Integer),
    Column("UnitPrice", Float)
)

但是，当我运行实际查询时，我收到此错误

Traceback (most recent call last):
  File "/workspace/PostGres_Chinook_Example/sql-expressions.py", line 15, in <module>
    meta = MetaData(db)
           ^^^^^^^^^^^^
  File "/workspace/.pip-modules/lib/python3.12/site-packages/sqlalchemy/sql/schema.py", line 5481, in __init__
    raise exc.ArgumentError(
sqlalchemy.exc.ArgumentError: expected schema argument to be a string, got <class 'sqlalchemy.engine.base.Engine'>.

我不确定我在哪里出了问题，可能是 sqlalchemy 的版本（我尝试更改它，但它完全抛出了不同的错误）

任何关于我在这里出错的地方的指示将不胜感激。

Answer 1

元数据独立于引擎而存在，因此您无需将它们显式地绑定在一起。 IE。不要将 db 传递给 MetaData()。

一旦完全定义了元数据（和表），您就可以使用引擎来创建元数据，例如

metadata.create_all(engine)

https://docs.sqlalchemy.org/en/20/core/metadata.html#creating-and-dropping-database-tables