id	summary	reporter	owner	description	type	status	priority	resolution	keywords	cc	topic	difficulty	mentor
1605	A universal data store interface.	gregweber		"A lack of a high-level data store library is a huge weakness in haskell.

Data storage is absolutely critical for web development or any program that needs to persist data or whose data processing exceeds memory. Haskell web development has languished in part because one had to choose between lower-level SQL or Happstack's experimental data store that uses only the process memory. All other widely used programming languages have multiple ORMs for proven databases. Haskell needs some better database abstraction libraries.

The persistent library is a universal data store interface that already has PostgreSQL, Sqlite, MySQL, MongoDB, and experimental CouchDB backend. Most users of the Yesod web framework are using it, and it is also being used outside of web development. With some more improvements, persistent could become the go-to data store interface for haskell programmers.

We could create interfaces to more databases, but the majority of Haskell programs just need *a* database, and would be happy with a really good interface to any database. There is also a need to interface with existing SQL databases. So I would like to focus on making (SQL & MongoDB) storage layers really good. MongoDB should be easier to create a great interface for.

We have moved Persistent in the direction of universal query interface to just a universal data store serialization interface. There are many critics of query interfaces for good reasons: we will never be able to solve all use cases.

I believe future work on Persistent should continue this recent direction of allowing for raw queries. One can now finally write raw SQL queries and get them automatically properly serialized. The next step is to make them extraordinarily type-safe. That is, we know at compile time that the queries are valid. They reference columns correctly and they are valid database queries. There is already an experimental implementation of this for SQL called persistent-hssqlppp that checks the validity of SQL statements at compile time.

Persistent's biggest limitation right now is the lack of a good technique for returning a projection of the data - we always give back a full record. This issue should be explored in the GSoC, but does not have to be solved.

Persistent already has a very good Quasi-Quoted DSL for creating a schema, but another task at hand is to write a convenient Template Haskell interface for declaring a schema. This should not be difficult because we already have all the tools in place.

There are also some possibilities for integrating with existing Haskell backends. One interesting option is integration with HaskellDB or DSH - HaskellDB does not automatically serialize to a Haskell record like Persistent does.

Michael Snoyman and Greg Weber are willing to mentor, and there is a large community of users willing to help or give feedback."	proposed-project	new	not yet rated				misc	unknown	not-accepted