SQLAlchemy

SQLAlchemy is an open-source Python library that provides a SQL toolkit and Object Relational Mapper (ORM) for database interactions. It allows developers to work with databases using Python objects, enabling efficient and flexible database access.

Description
SQLAlchemy offers tools for database schema generation, querying, and object-relational mapping. Key features include:


 * A comprehensive SQL expression language for constructing and executing SQL queries.
 * A powerful ORM that allows the mapping of Python classes to database tables.
 * Support for database schema migrations.
 * Compatibility with multiple database backends.
 * Tools for database connection pooling and transaction management.

History
SQLAlchemy was first released in February 2006. It has evolved to include a wide range of features for database interaction and has gained popularity among Python developers. Notable versions include:


 * Version 0.1 (2006): Initial release.
 * Version 1.0 (2015): Major enhancements in ORM and SQL expression language.
 * Version 1.4 (2021): Introduction of a new ORM API.

Example
The following example represents an n-to-1 relationship between movies and their directors. It is shown how user-defined Python classes create corresponding database tables, how instances with relationships are created from either side of the relationship, and finally how the data can be queried — illustrating automatically generated SQL queries for both lazy and eager loading.

Schema definition
Creating two Python classes and corresponding database tables in the DBMS:

Data insertion
One can insert a director-movie relationship via either entity:

Querying
SQLAlchemy issues the following query to the DBMS (omitting aliases):

The output:

Setting  (default) instead, SQLAlchemy would first issue a query to get the list of movies and only when needed (lazy) for each director a query to get the name of the corresponding director: