Strictly typed SQL with Contra CTO, Gajus Kuizinas

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Nov 20, 2025

Gajus Kuizinas, co-founder and CTO of Contra, shares insights on creating high-ownership engineering cultures and developing strict runtime-validated SQL through his Slonik library. He discusses the frustrations of traditional ORMs, the breakthrough of JavaScript template tags for safe SQL, and the innovative SafeQL for real-time schema checks. Gajus also introduces Loom-driven development, a tactic for speeding up reviews and improving context. Tune in to explore the evolution of developer experience and schema integrity!

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INSIGHT

Raw SQL With Safer Template Tags

Raw SQL plus template tags preserves readability while preventing injection by sending strings and parameters separately.
Gajus argues this keeps queries debuggable and avoids costly ORM learning curves.

ADVICE

Validate Every Query At Runtime

Add runtime validation for every query to catch schema drift early using Zod or similar tools.
Prioritize loud failures so you fix contract mismatches before they silently corrupt behavior.

INSIGHT

Composable SQL Fragments

SQL template fragments are composable objects that can be merged and renumber parameter binds automatically.
This enables conditional query composition while keeping the final SQL readable and validated.

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In this episode, Gajus Kuizinas, co-founder and CTO of Contra, joins Aaron to talk about building the engineering world you want to live in, from strict runtime-validated SQL with Slonik to creating high-ownership engineering cultures. They dive into developer experience, runtime assertions, SafeQL, and even “Loom-driven development,” a powerful review process that lets teams move fast without breaking things.

Follow Gajus:
Twitter/X: https://twitter.com/kuizinas
Slonk: https://github.com/gajus/slonik
Scaling article: https://gajus.medium.com/lessons-learned-scaling-postgresql-database-to-1-2bn-records-month-edc5449b3067

Follow Aaron:
Twitter/X: https://twitter.com/aarondfrancis
Database School: https://databaseschool.com
Database School YouTube Channel: https://www.youtube.com/@UCT3XN4RtcFhmrWl8tf_o49g (Subscribe today)
LinkedIn: https://www.linkedin.com/in/aarondfrancis
Website: https://aaronfrancis.com - find articles, podcasts, courses, and more.

Chapters:
00:00 – Introduction
01:03 – Meet Gajus and Contra
01:48 – What Contra does and how it’s different
05:34 – Why Slonik exists & early career origins
07:47 – The early Node.js era and frustrations with ORMs
09:50 – SQL vs abstractions and the case for raw SQL
10:35 – Template tags and the breakthrough idea
12:03 – Strictness, catching errors early & data shape guarantees
13:37 – Runtime type checking, Zod, and performance debates
16:02 – SafeQL and real-time schema linting
17:01 – Synthesizing Slonik’s philosophy
21:29 – Handling drift, static types vs reality
22:52 – Defining schemas per-query & why it matters
27:59 – Integrating runtime types with large test suites
31:00 – Scaling the team and performance tradeoffs
33:41 – Runtime validation cost vs developer productivity
35:21 – Real drift examples from payments & external APIs
38:21 – User roles, data shape differences & edge cases
39:51 – Integration test safety & catching issues pre-deploy
40:52 – Contra’s engineering culture
41:47 – Why traditional PR reviews don’t scale
43:22 – Introducing Loom-Driven Development
45:12 – How looms transformed the review process
52:38 – Using GetDX to measure engineering friction
53:07 – How the team uses AI (Claude, etc.)
56:26 – Closing thoughts on DX and engineering philosophy
58:05 – Contra needs Postgres experts
59:00 – Where to find Gajus