Re: [sqlalchemy] alembic handles no primary key table

[Werner]

On 01/12/2012 17:49, junepeach wrote:
I have 2 simple tables defined as below:
class Test1(Base):
     __tablename__ = 'test1'
     id = Column(Integer, primary_key = True)
     name = Column(String(15))
class Test2(Base):
     __tablename__ = 'test2'
     fid = Column(Integer, ForeignKey('test1.id'))
     tname = Column(String(15))

You can see that Test2 is a table without a primary key. When I run 'alembic 
revision --autogenerate' to create migration script, and got below error:
   File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/__init__.py", 
line 1129, in mapper
     return Mapper(class_, local_table, *args, **params)
   File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/mapper.py", line 
203, in __init__
     self._configure_pks()
   File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/mapper.py", line 
767, in _configure_pks
     (self, self.mapped_table.description))
sqlalchemy.exc.ArgumentError: Mapper Mapper|Test2|test2 could not assemble any 
primary key columns for mapped table 'test2'

So I wonder how to create a migration script for a table without primary key. 
Non-primary key is not good design, but acceptable in mysql, sqlite, postgresql.
Not an expert, but above is using the SA orm which requires a primary 
key, you need to define the table using:
http://sqlalchemy.readthedocs.org/en/rel_0_8/core/schema.html#metadata-describing

Werner

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