Hey everybody,
The purpose of this thread is to answer three questions:

1. How do we go about upgraging an Ecto 2.2.x adapter that is not on the latest 2.2.x version, to the latest 2.2.x version?
2. How do we go about upgraging an adapter that is at the latest Ecto 2.2.x version, to Ecto 3.1.x?
3. How do we go about making an Ecto 3.1.x adapter from scratch?

I apologise to the people I mentioned via an @ in advance. Making this crystal clear here and now: I do not ask those people to produce any code, I am asking them only to help me gather an authoritative collection of informational resources to get me and other interested maintainers started.

I would like to modernise the Sqlite database support in Elixir. This means two things:

1. (OPTIONAL) Contribute to sqlite_ecto2 so it works with the latest Ecto 2.2.x version (as of the time of this post, 2.2.12). This is mostly for exercise and to dip my toes and hopefully learn well how to approach the Ecto 3.1.x work. If this proves to consume unjustified amounts of energy and time and/or turns out to be unrelated to the Ecto 3.1.x work then I might drop it.

2. (MAIN GOAL) Make a new library that brings Sqlite to Ecto 3.1.x (as of the time of this post, 3.1.6).

I have tracked several resources:

• Sqlite_ecto2 new maintainer (post by @ConnorRigby in ElixirForum)
• Version working with ecto 3 (sqlite_ecto2 GitHub issue)
• Instructions on how to contibute (sqlite_ecto2 GitHub issue)

@michalmuskala Pointed at two useful pages to get new maintainers started here:

• Upgrading to DBConnection 2.0 (db_connection GitHub issue)
• Ecto 3.0 CHANGELOG on adapter changes from 2.2 (ecto GitHub changelog)

There is also another post on his blog – Creating Ecto Adapters – but it’s from 2015 and I am not sure if it’s still relevant.

@jwarlander contributed a link to the MyXQL adapter development blog series: Building a new MySQL adapter for Ecto, Part I: Hello World (links to the rest of the articles are inside this one, and every subsequent one as well).

Additional honorable mentions with a plea for other and/or more modern articles: @josevalim, @ericmj, @wojtekmach, @fishcakez and @whatyouhide.