Brief introduction to Opaleye 
Opaleye is a Haskell library that provides an SQL-generating embedded domain specific language for targeting Postgres. You need Opaleye if you want to use Haskell to write typesafe and composable code to query a Postgres database.
"Opaleye really is great. You've managed to bring what is so wonderful about relational databases and give it type safety and composition (i.e. what is wonderful about Haskell)" – Daniel Patterson, Position Development
"We use it for most of our DB code. It's very flexible and almost always as performant as manually written queries" – Adam Bergmark, Silk.co
"Opaleye is absolutely fantastic. It has been solid in production for years!" – Matt Wraith
"Opaleye just works, and it’s my personal recommendation ... I like it a lot" – William Yao
Opaleye allows you to define your database tables and write queries against them in Haskell code, and aims to be typesafe in the sense that if your code compiles then the generated SQL query will not fail at runtime. A wide range of SQL functionality is supported including inner and outer joins, restriction, aggregation, distinct, sorting and limiting, unions and differences. Facilities to insert to, update and delete from tables are also provided. Code written using Opaleye is composable at a very fine level of granularity, promoting code reuse and high levels of abstraction.
Getting Opaleye
- Github: https://github.com/tomjaguarpaw/haskell-opaleye
- Hackage: https://hackage.haskell.org/package/opaleye
Tutorials
Please get started with Opaleye by referring to these two tutorials
Advanced
Contact
Contact the author
The main author of Opaleye is Tom Ellis. He can be contacted via email.
File bugs
Please file bugs on the Opaleye GitHub issue tracking page.
Discuss and ask questions about Opaleye
You are welcome to use the Opaleye GitHub issue tracking page for discussion of or questions about Opaleye even if they don't relate to a bug or issue.
PRs
You are welcome to make PRs to Opaleye. If you would like to discuss the design of your PR before you start work on it feel free to do so by filing a new issue.
Internal modules
Opaleye exports a number of modules named Opaleye.Internal.....
They are provided in case of urgent need for access to the internals,
but they are not intended to be used by API consumers and if you find
yourself repeatedly accessing them this is a sign that either you or
Opaleye are doing something wrong. In such a case please file a bug.
The interface of Internal modules does not follow the PVP and may
break between minor releases, so be careful.
Running tests
You must have running PostgreSQL server to run tests. Specify the database
by setting the POSTGRES_CONNSTRING environment variable:
POSTGRES_CONNSTRING="user=tom dbname=opaleye_test" stack test
Commercial support
Commercial support for Opaleye is provided by Purely Agile.
Backup maintainers
In the event of the main developer becoming unreachable, please contact the following who are authorised to make bugfixes and dependency version bumps:
- Adam Bergmark
- Erik Hesselink
- Oliver Charles
Contributors
The Opaleye Project was founded by Tom Ellis, inspired by theoretical work on databases by David Spivak. Much of the implementation was based on ideas and code from the HaskellDB project by Daan Leijen, Conny Andersson, Martin Andersson, Mary Bergman, Victor Blomqvist, Bjorn Bringert, Anders Hockersten, Torbjorn Martin, Jeremy Shaw and Justin Bailey.
The following individuals and organisations made helpful contributions which were important in helping to get the project off the ground.
- Silk (Erik Hesselink, Adam Bergmark)
- Karamaan (Christopher Lewis)
- Fynder (Renzo Carbonara, Oliver Charles)
- Daniel Patterson
- Jakub Ryška
- Travis Staton
Joseph Abrahamson, Alfredo Di Napoli and Mietek Bak performed useful reviews of early versions which helped improve the codebase. Since then there have been helpful contributions from many others. Thanks to them all for their help.