ZODB

ZODB, short for Zope Object Database, is a native object database for Python. It stores Python objects directly rather than mapping them to rows in a relational database. This makes it well suited for applications that manage complex, interconnected object graphs, and it has been widely used in Zope-based projects such as Plone. ZODB can be used standalone or as part of larger web frameworks.

Core features include persistent objects, transactions, and ACID guarantees. Objects are instances of persistent classes or wrapped in persistent containers, and changes are recorded via a transaction manager with two-phase commit to ensure atomicity. ZODB uses an in-memory cache for performance and supports multi-version concurrency control to allow concurrent readers.

Storage backends include FileStorage for on-disk storage, ZEO for client-server configurations that let multiple processes or machines access the same database, and RelStorage which writes to relational databases such as PostgreSQL, MySQL, or SQLite. Blob storage is available via the ZODB blob extension for large binary data.

Usage typically involves connecting to a ZODB database, obtaining the root object, and creating or modifying persistent objects. Changes are made within a transaction and committed with the transaction module; reads occur through persistent references. The database exposes the object graph directly to Python code, without requiring SQL.

ZODB has a long association with Zope and Plone and is widely used in Python-based applications that require complex data models. It is not always the best choice for applications requiring ad-hoc SQL queries or simple relational schemas. The project remains active with ongoing development of new backends and features.