multi-target sources

[fwbrasil]

Version: (e.g. 0.6.0)
Module: (e.g. quill-core)

Problem

Quill doesn't provide an easy way to switch to a different SQL dialect at runtime. Queries are generated at compile time and the application needs to be recompiled in order to run on another target dialect.

Solution

Introduce multi-target sources, that generate queries against multiple compatible target sources at compile-time and allows the user to choose the target source type at runtime.

By "compatible" target sources I mean sources that have the exact same method signatures. For instance, it'd be possible to have a

val s = source(new MultiSourceConfig(new JdbcConfig[SnakeCase, MysqlDialect]("mysql"), new JdbcConfig[Literal, H2Dialect]("h2"))

but not

val s = source(new MultiSourceConfig(new JdbcConfig[SnakeCase, MysqlDialect]("mysql"), new AsyncSource[Literal, H2Dialect]("h2")))

The macro would generate a message for all targets:

case class Person(fullName: String)

val s = source(new MultiSourceConfig(new JdbcConfig[SnakeCase, MysqlDialect]("mysql"), new JdbcConfig[Literal, H2Dialect]("h2"))

s.run(query[Person])
// compilation message
// mysql: SELECT full_name FROM person
// h2: SELECT fullName from Person

@getquill/maintainers

[mxl]

Workaround
You can build your application for each context to separate artefacts (jars) and make some supervisor process to stop application with one context and start with another.
See https://gitter.im/getquill/quill?at=58498469c29531ac5d393595.
Also this's useful for those who just want to build application for different environment like test and prod with different contexts.

[mxl]

I made an example project showing how to switch between MySQL and H2 JDBC contexts at compile-time. Do not forget to checkout quill-multiple-jdbc-contexts branch.

[mxl]

If someone needs to switch between sync (e. g. H2JdbcContext) and async (e. g. PostgresAsyncContext) then take a look at this sample project (checkout quill-multiple-mixed-contexts branch).

[fwbrasil]

@getquill/maintainers I've been thinking about this feature but I couldn't find a good way to implement it. I think I'll remove it from the 2.0 plans. It's too complex and I don't see push from the community to have it. Wdyt?

[fwbrasil]

I forgot to mention something. Even without this feature, users still can use multiple contexts using @mxl's approach or falling back to dynamic queries using #886

[mxl]

@fwbrasil 👌 We receive questions about context switching on Gitter channel occasionally. But people usually ask about compile-time context switching which can be done by above workaround though it does not work in all cases (for example, when switching sync and async contexts). I think that fixing bugs is top priority now and this feature can wait.

[mielientiev]

any progress or plans to resolve this issue?

[mosyp]

@getquill/maintainers I suggest to close this in favor of #971, since introducing multi-target sources should be avoided in favor of generating queries using idioms and io monad. Wdyt?