Sustained is a Python query builder, lightweight ORM, and schema migration tool, originally inspired by Objection.js. You define one set of model classes to describe your tables. Sustained builds and runs the queries against them, and keeps the schema itself in step.

The syntax will look familiar if you have worked with Objection, Kysely, or even knex before:

adults = User.query().where(User.c.age >= 18).orderBy('name').run()

Managing queries through Sustained

With Sustained, you can:

• Build SQL programmatically. Selects, aggregates, window functions, CASE expressions, every join type, CTEs (including recursive), unions, INTERSECT and EXCEPT, subqueries in SELECT, FROM, WHERE, and JOIN clauses.
• Target seven dialects. ANSI (default), PostgreSQL, MySQL and MariaDB, MSSQL, Presto, AWS Athena, and DuckDB. Quoting, placeholders, upsert syntax, LIMIT/OFFSET spelling, and function names all follow the dialect. Unsupported features raise DialectError at build time instead of failing in the database. Migrating queries between dialects is a one-line change.
• Execute queries safely. Every statement runs parameterized against any DB-API 2.0 connection or a ConnectionPool. Transactions nest through savepoints. update() and delete() refuse to run without a WHERE clause.
• Write data. insert(), update(), delete(), upserts through onConflict(), INSERT ... SELECT, CREATE TABLE AS, and RETURNING.
• Hydrate results. Rows become model instances, plain dicts, pandas DataFrames, or pyarrow Tables. Relations eager load with withGraphFetched(). A type checker reads Show.query().run() as List[Show].
• Run queries async. The same queries run through driver adapters with await query.arun(), including asyncpg and aiosqlite. AsyncConnectionPool pools those adapters, so concurrent queries do not queue behind one connection.

Schema management with Sustained

Sustained also manages schema changes. It generates migrations from your models, tests each change before it runs, and rolls a migration back when you ask. These features are described in detail at Schema and Migrations.

With Sustained, schema migrations are:

• Generated from your models. Migrator.up(models=[...]) diffs the live database against your models, generates the migration, records it, and applies it. Run it again after a model change and only the difference is applied. down() rolls it back.
• Rehearsed before they land. sustained rehearse applies every pending migration, runs the downgrade steps to test the revert plan, and rolls the whole thing back. A migration that fails to run, or fails to reverse, is reported before it reaches the real schema. A config module can send the rehearsal to a scratch database instead.
• Planned in one screen. sustained plan shows your pending migrations, outstanding problems that validate would report, and any gap between your models and the database’s current state.
• Verified before every run. Sustained keeps a per-database tracking table that records a sequence number, a SHA-256 checksum, an apply timestamp, execution time, and a success flag per migration. validate refuses a run when a migration was edited after it ran, arrives out of order, or left a failed attempt behind. repair will delete failed runs from the tracking table and update script checksums after manual corrections.
• Gated by custom safeguards. A guard is a built-in rule such as no_drops(), index_must_be_concurrent(), or max_statements(n), or a function you write. Guards read every statement a run would apply and block the deployment when a rule fails.
• Safe by default. Drops need explicit allow_drops=True, renames need explicit hints, NOT NULL changes need a default or backfill. Destructive changes will never run by default.
• Written your way. Migrations can be Python Migration objects, <id>.up.sql and <id>.down.sql files with ${placeholders}, or <id>.repeat.sql files for views and seed data, which re-run whenever their contents change.
• Ready for deploys. The sustained console script runs plan, status, rehearse, migrate, down, validate, repair, script, and baseline, with exit codes for pipelines and before_migrate, after_migrate, and on_error callbacks around a run. Concurrent deploys queue on an advisory lock. baseline adopts a database that already matches. script('up') renders the SQL for a DBA instead of running it. AsyncMigrator does all of it on an async adapter.

Finding your way

New here? Getting Started builds a working application in one sitting: a schema that Sustained creates, queries that join across tables, a scripted generated migration, and the same migrations run interactively from the shell. It needs nothing but SQLite to run.

Have a task in mind? Recipes pairs each common task with the code that does it.

Looking up a method? The API Reference gives every public name its signature, return type, and the conditions that raise.

The guides each explain one area in depth, and they build on each other in this order:

You want to	Read
Map classes to tables, catch column typos	Models
Build a SELECT: columns, functions, CTEs, unions, pagination	Queries
Target a specific engine, pick a driver	SQL Dialects
Filter rows: where methods and typed predicates	Filtering
Aggregate and filter groups	Grouping
Join tables and define relations	Relations and Joins
Run queries, write data, transactions, pooling, async	Executing Queries
Create tables, rehearse, generate and roll back migrations	Schema and Migrations

Released versions are listed in the Changelog.

Installing

python3 -m pip install sustained

Sustained has no required dependencies. pandas and pyarrow are optional, and only to_df() and to_arrow() need them.