Question

背景

我是SQLAlchemy的新手，对于我应该如何选择东西似乎相当混乱。

我的mysql数据库中有一个表叫做基因，我有gene_id，gene_description和gene_symbol

我想做什么：

我想做的只是一个简单的选择查询：

class Bar
{
    ...
    Foo& wholeThing;

    Bar(Foo& f) :
        wholeThing(f)      // <=--- HERE
    {
                           // <=--- empty
    }

    void printvariable(void)
    {
        cout << "f.a is " << wholeThing.a << endl;
    }

但我似乎对如何实现这个目标感到困惑

以下是我的工作：

Select * from Genes

问题：

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)

还有某种类型的“intellisense”我可以做一些像gene_table = engine.Gene这样的事情。如果我没有错误，有一种方法可以用映射做到这一点，但它对我不起作用

编辑：这可能会有所帮助：

How to automatically reflect database to sqlalchemy declarative?

Answer 1

因此我们可以使用反射而不必显式创建类，但如果我们想要速度，我们可以使用sqlautocode创建它们，如下所述：

Reverse engineer SQLAlchemy declarative class definition from existing MySQL database?

此外，mysql数据库存在一个问题，它会出现如下错误:(取自bitbucket：https://bitbucket.org/zzzeek/sqlalchemy/issues/1909/reflection-issue-with-mysql-url-with-no）

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'

通过添加数据库名称（您正在使用的名称）解决此问题，如下所示：

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

我用它来正确连接： http://docs.sqlalchemy.org/en/latest/orm/extensions/automap.html 还有这个： http://docs.sqlalchemy.org/en/latest/core/engines.html

这也可能有所帮助： How to automatically reflect database to sqlalchemy declarative?

我的代码最终看起来像这样：

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 )

SQLAlchemy - 简单的select语句

1 个答案: