Python SQLAlchemy Basic Structure -


i have been watching few videos , reading various posts try , understand basic structure of sqlalchemy in python script.

can tell me:

  1. why below script fails

script:

from sqlalchemy import * sqlalchemy.ext.declarative import declarative_base  base = declarative_base()  class records(base):     __tablename__ = 'records'      data1 = column(text())     data2 = column(text())     data3 = column(text())     data4 = column(text())    if __name__ == "__main__":     engine = create_engine('mysql://user:password@localhost/database')     base.metadata.create_all(bind=engine, checkfirst=true)

it fails with 

traceback (most recent call last):   file "sqltest.py", line 6, in <module>     class records(base):   file "build/bdist.linux-x86_64/egg/sqlalchemy/ext/declarative/api.py", line 55, in __init__   file "build/bdist.linux-x86_64/egg/sqlalchemy/ext/declarative/base.py", line 88, in _as_declarative   file "build/bdist.linux-x86_64/egg/sqlalchemy/ext/declarative/base.py", line 103, in setup_mapping   file "build/bdist.linux-x86_64/egg/sqlalchemy/ext/declarative/base.py", line 135, in __init__   file "build/bdist.linux-x86_64/egg/sqlalchemy/ext/declarative/base.py", line 138, in _early_mapping   file "build/bdist.linux-x86_64/egg/sqlalchemy/ext/declarative/base.py", line 530, in map   file "<string>", line 2, in mapper   file "build/bdist.linux-x86_64/egg/sqlalchemy/orm/mapper.py", line 629, in __init__   file "build/bdist.linux-x86_64/egg/sqlalchemy/orm/mapper.py", line 1223, in _configure_pks sqlalchemy.exc.argumenterror: mapper mapper|records|records not assemble primary key columns mapped table 'records'

am forced use primary key? or way call records class?

as error message indicates primary key mandatory. no reason not have 1 anyways, otherwise wont able express table relationships.

in response comment: if rely on using existing database scheme lacks primary keys can try zzzeek (the author of sqlalchemy) proposed in comment question: sqlalchemy declarative: table without primary keys?, use example

__mapper_args__ = {"primary_key":(data1, data2)}}

if (data1, data2) identify table row. , there should way identify table table row, otherwise have severe design problem.


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