Welcome to Rel8!

Welcome to Rel8! Rel8 is a Haskell library for interacting with PostgreSQL databases, built on top of the fantastic Opaleye library.

The main objectives of Rel8 are:

• Conciseness: Users using Rel8 should not need to write boiler-plate code. By using expressive types, we can provide sufficient information for the compiler to infer code whenever possible.

• Inferrable: Despite using a lot of type level magic, Rel8 aims to have excellent and predictable type inference.

• Familiar: writing Rel8 queries should feel like normal Haskell programming.

Getting Started

• Getting Started
  • The Example Schema
  • Mapping Schemas to Haskell
  • Writing Queries

Rel8 concepts

• DBType
  • Combining newtype and DBType
  • Parsing with DBType
  • Deriving DBType via ReadShow
  • Storing structured data with JSONEncoded
  • The DBType subtypes
• Expr and Sql
  • Expr
  • null
  • SQL and null-polymorphic expressions
• Tables
  • Expr is a single-column table
  • Tuples combine tables
  • Custom table types
• Writing queries with Query
  • Understanding the Query monad
  • Selecting rows from tables
  • Limit and offset
  • Filtering queries
  • Inner joins
  • Left (outer) joins with optional
  • Ordering results
  • Aggregating queries
  • Set operations
• INSERT, UPDATE and DELETE
  • DELETE
  • UPDATE
  • INSERT
  • RETURNING
  • Default values

Tips and tricks

• Cookbook

More Resources

• The Haskell API documentation describes how individual functions are types are to be used.

• If you have a question about how to use Rel8, feel free to open a GitHub discussion.

• If you think you’ve found a bug, confusing behavior, or have a feature request, please raise an issue at Rel8’s issue tracker.