SQLAlchemy - 簡單的select語句

Question

背景：

我是SQLAlchemy的新手，對於我應該如何選擇東西似乎相當混亂。

我的mysql數據庫中有一個表叫做基因，我有gene_id，gene_description和gene_symbol

我想做的事：

我想做的只是一個簡單的選擇查詢：

Select * from Genes

但我似乎對如何實現這一目標感到困惑

這是我做的：

import sqlalchemy
from sqlalchemy.orm import sessionmaker
from sqlalchemy.ext.automap import automap_base
import csv
import pandas as pd

engine = sqlalchemy.create_engine('mysql://root:toor@localhost') # connect to server
metadata = sqlalchemy.MetaData(bind=engine)
engine.execute("USE TestDB")

genes = sqlalchemy.table('Genes')
s = sqlalchemy.select([genes])
engine.execute(s)

問題：

ProgrammingError: (_mysql_exceptions.ProgrammingError) (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'FROM `Genes`' at line 2") [SQL: u'SELECT  \nFROM `Genes`']

還有一些類型的“intellisense”，我可以做一些像gene_table = engine.Gene。 如果我沒有錯誤，有一種方法可以用映射做到這一點，但它對我不起作用

編輯：這可能會有所幫助：

如何自動將數據庫反映到sqlalchemy聲明中？

Answer 1

所以我們可以使用反射而不必顯式創建類，但如果我們想要速度，我們可以使用sqlautocode創建它們，如下所述：

從現有的MySQL數據庫中反向設計SQLAlchemy聲明性類定義？

此外，mysql數據庫存在一個問題，它會產生如下錯誤:(取自bitbucket： https ：//bitbucket.org/zzzeek/sqlalchemy/issues/1909/reflection-issue-with-mysql-url - 沒有 ）

SNIP...
File "/opt/buildout-eggs/SQLAlchemy-0.6.4-py2.5.egg/sqlalchemy/schema.py", line 1927, in __init__
    self.reflect()
  File "/opt/buildout-eggs/SQLAlchemy-0.6.4-py2.5.egg/sqlalchemy/schema.py", line 2037, in reflect
    connection=conn))
  File "/opt/buildout-eggs/SQLAlchemy-0.6.4-py2.5.egg/sqlalchemy/engine/base.py", line 1852, in table_names
    return self.dialect.get_table_names(conn, schema)
  File "<string>", line 1, in <lambda>
  File "/opt/buildout-eggs/SQLAlchemy-0.6.4-py2.5.egg/sqlalchemy/engine/reflection.py", line 32, in cache
    return fn(self, con, *args, **kw)
  File "/opt/buildout-eggs/SQLAlchemy-0.6.4-py2.5.egg/sqlalchemy/dialects/mysql/base.py", line 1791, in get_table_names
    self.identifier_preparer.quote_identifier(current_schema))
  File "/opt/buildout-eggs/SQLAlchemy-0.6.4-py2.5.egg/sqlalchemy/sql/compiler.py", line 1517, in quote_identifier
    return self.initial_quote + self._escape_identifier(value) + self.final_quote
  File "/opt/buildout-eggs/SQLAlchemy-0.6.4-py2.5.egg/sqlalchemy/dialects/mysql/mysqldb.py", line 77, in _escape_identifier
    value = value.replace(self.escape_quote, self.escape_to_quote)
AttributeError: 'NoneType' object has no attribute 'replace'

這可以通過添加數據庫名稱（您正在使用的名稱）來解決，如下所示：

engine = create_engine('mysql+mysqldb://USER_NAME:PASSWORD@127.0.0.1/DATABASE_NAME', pool_recycle=3600) # connect to server

我使用它來正確連接： http ： //docs.sqlalchemy.org/en/latest/orm/extensions/automap.html和這： http ： //docs.sqlalchemy.org/en/latest/core/engines.html

這也可能有所幫助： 如何自動將數據庫反映到sqlalchemy聲明中？

我的代碼最終看起來像這樣：

from sqlalchemy.ext.automap import automap_base
from sqlalchemy.orm import Session
from sqlalchemy import create_engine

Base = automap_base()

# engine, suppose it has two tables 'user' and 'address' set up
engine = create_engine('mysql+mysqldb://root:toor@127.0.0.1/TestDB', pool_recycle=3600) # connect to server

# reflect the tables
Base.prepare(engine, reflect=True)

# mapped classes are now created with names by default
# matching that of the table name.
Genes = Base.classes.Genes

Address = Base.classes.address
#Start Session
session = Session(engine)
#add a row:
session.add(Genes(Gene_Id=1,Gene_Symbol = "GENE_SYMBOL", Gene_Description="GENE_DESCRIPTION"))
session.commit()
q = session.query(Genes).all()
for gene in q:
    print "This is the Gene ID {},\n This is the Gene Desc {},\n this is the Gene symbol {}.".format(gene.Gene_Id,gene.Gene_Description, gene.Gene_Symbol )