sqlacodegen

This is a tool that reads the structure of an existing database and generates the appropriate SQLAlchemy model code, using the declarative style if possible.

This tool was written as a replacement for sqlautocode_, which was suffering from several issues (including, but not limited to, incompatibility with Python 3 and the latest SQLAlchemy version).

.. _sqlautocode: http://code.google.com/p/sqlautocode/

Features

• Supports SQLAlchemy 0.8.x - 1.3.x
• Produces declarative code that almost looks like it was hand written
• Produces PEP 8_ compliant code
• Accurately determines relationships, including many-to-many, one-to-one
• Automatically detects joined table inheritance
• Excellent test coverage

.. _PEP 8: http://www.python.org/dev/peps/pep-0008/

Usage instructions

Installation

To install, do::

pip install sqlacodegen

Example usage

At the minimum, you have to give sqlacodegen a database URL. The URL is passed directly to SQLAlchemy's create_engine()_ method so please refer to SQLAlchemy's documentation_ for instructions on how to construct a proper URL.

Examples::

sqlacodegen postgresql:///some_local_db
sqlacodegen mysql+oursql://user:password@localhost/dbname
sqlacodegen sqlite:///database.db

To see the full list of options::

sqlacodegen --help

.. _create_engine(): http://docs.sqlalchemy.org/en/latest/core/engines.html#sqlalchemy.create_engine .. _SQLAlchemy's documentation: http://docs.sqlalchemy.org/en/latest/core/engines.html

Why does it sometimes generate classes and sometimes Tables?

Unless the --noclasses option is used, sqlacodegen tries to generate declarative model classes from each table. There are two circumstances in which a Table is generated instead:

• the table has no primary key constraint (which is required by SQLAlchemy for every model class)
• the table is an association table between two other tables (see below for the specifics)

Model class naming logic

The table name (which is assumed to be in English) is converted to singular form using the "inflect" library. Then, every underscore is removed while transforming the next letter to upper case. For example, sales_invoices becomes SalesInvoice.

Relationship detection logic

Relationships are detected based on existing foreign key constraints as follows:

• many-to-one: a foreign key constraint exists on the table
• one-to-one: same as many-to-one, but a unique constraint exists on the column(s) involved
• many-to-many: an association table is found to exist between two tables

A table is considered an association table if it satisfies all of the following conditions:

#. has exactly two foreign key constraints #. all its columns are involved in said constraints

Relationship naming logic

Relationships are typically named based on the opposite class name. For example, if an Employee class has a column named employer which has a foreign key to Company.id, the relationship is named company.

A special case for single column many-to-one and one-to-one relationships, however, is if the column is named like employer_id. Then the relationship is named employer due to that _id suffix.

If more than one relationship would be created with the same name, the latter ones are appended numeric suffixes, starting from 1.

Getting help

If you have problems or other questions, you can either:

• Ask on the SQLAlchemy Google group_, or
• Ask on the #sqlalchemy channel on Freenode IRC_

.. _SQLAlchemy Google group: http://groups.google.com/group/sqlalchemy .. _Freenode IRC: http://freenode.net/irc_servers.shtml