SQLAlchemy Automap does not create class for tables without primary key
python, sqlalchemy
Solution
Figured it out by combing through the reference/reframing the problem.
In case it helps someone else -
Because SQLAlchemy ORM is based on an identity map model, one cannot map (or automap) a table that does not have a primary key. An arbitrary primary key should be specified.
http://docs.sqlalchemy.org/en/latest/faq/ormconfiguration.html#how-do-i-map-a-table-that-has-no-primary-key
Problem
I am using SQL Alchemy v(0.9.1) which has the automap functionality. This allows me to create classes and relationships automatically. http://docs.sqlalchemy.org/en/rel_0_9/orm/extensions/automap.html The problem I am experiencing is that when using automap_base, I see that not all the tables that are available in the metadata.tables list are mapped. There are no errors when preparing, except that I am unable to access the class (e.g. Base.classes.Example_Table) from the Base after calling automap_base() ``` from sqlalchemy import create_engine, MetaData from sqlalchemy.orm import create_session from sqlalchemy.ext.automap import automap_base engine = create_engine("mysql+mysqldb://") Base = automap_base() Base.prepare(engine, reflect = True) session = create_session(bind = engine) ``` Then I run to find that classes do not exist for all tables in metadata (I did not use only = [] argument in metadata) ``` for mappedclass in Base.classes: print mappedclass for mdtable in metadata.tables: print mdtable ``` Only to find that Example_Table (with the following create syntax) does not have a class ``` CREATE TABLE `Example_Table` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `attributeType` varchar(255) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=3290719 DEFAULT CHARSET=latin1 ``` i.e. Base.class.Example_Table returns the following error ``` --------------------------------------------------------------------------- AttributeError Traceback (most recent call last) <ipython-input-15-94492ae1b8ba> in <module>() 7 type(metadata.tables) 8 ----> 9 Base.classes.Example_Table /usr/local/lib/python2.7/site-packages/sqlalchemy/util/_collections.pyc in __getattr__(self, key) 172 return self._data[key] 173 except KeyError: --> 174 raise AttributeError(key) 175 176 def __contains__(self, key): AttributeError: Example_Table ``` I don't think this problem happens because my Example_Table name has an underscore in it. I think the problem is related to the fact that my Example_Table does not have a primary key. The Example_Table is only meant to link two other tables.