Bye Bye Mongo, Hello Postgres

Re:Bye Bye Mongo, Hello Postgres by QuinnWilton on Wednesday December 19, 2018 @06:24PM (#18720955)

Elixir's primary database wrapper, Ecto [0], lets you dynamically build queries at runtime, and also isn't an ORM. Here's two examples directly from the docs:

  # Query all rows in the "users" table, filtering for users whose age is > 18, and selecting their name
  "users"
  |> where([u], u.age > 18)
  |> select([u], u.name)

  # Build a dynamic query fragment based on some parameters
  dynamic = false
  
  dynamic =
    if params["is_public"] do
      dynamic([p], p.is_public or ^dynamic)
    else
      dynamic
    end
  
  dynamic =
    if params["allow_reviewers"] do
      dynamic([p, a], a.reviewer == true or ^dynamic)
    else
      dynamic
    end
  
  from "posts", where: ^dynamic

Across all the different means of interacting with a database I have experience with (from full-fledged ORMs like ActiveRecord, to sprocs in ASP.NET), I've found that it offers the best compromise between providing an ergonomic abstraction over the database, and not hiding all of the nitty-gritty details you need to worry about in order to write performant queries or use database-specific features like triggers or window functions.

My main point, though, is that you don't need to reach for NoSQL if all you need is a way to compose queries without string interpolation.

[0] https://github.com/elixir-ecto/ecto

[ Parent | on HN ]

Re:Bye Bye Mongo, Hello Postgres by quietbritishjim on Wednesday December 19, 2018 @08:08PM (#18721651)

As I said to a sibling response, this is not a substitute for Mongo's aggregation pipeline unless it can do analogous things to Postgres's JSONB fields. For example, can it unwind an array field, match those subrecords where one field (like a "key") matches a value and another field (like a "value") exceeds an overall value, and then apply this condition to filter the overall rows in the table?

Also, one of the benefits of Mongo's API is that it has excellent native implementations in numerous languages (we already use C++ and Python), so a suggestion to switch language entirely is not really equivalent.

[ Parent | on HN ]

Re:Bye Bye Mongo, Hello Postgres by inferiorhuman on Wednesday December 19, 2018 @09:01PM (#18721925)

> As I said to a sibling response, this is not a substitute for Mongo's aggregation pipeline

Huh? The aggregation framework is a solution to a mongo-only problem. Most other databases are performant, but Mongo suffers wildly from coarse locking and slow performance putting things into and retrieving things from the javascript VM.

> For example, can it unwind an array field, match those subrecords where one field (like a "key") matches a value and another field (like a "value") exceeds an overall value, and then apply this condition to filter the overall rows in the table?

This sounds suspiciously like a SQL view.

Edit: But if you actually need an array in a cell, Postgres has an array type that's also a first-class citizen with plenty of tooling around it.

[ Parent | on HN ]

Re:Bye Bye Mongo, Hello Postgres by quietbritishjim on Wednesday December 19, 2018 @09:39PM (#18722065)

The "this" was referring to dynamically building queries (the GP comment by me) in Ecto (the parent comment by QuinnWilton). What you've said is a non-sequitur in the context of this little discussion. My whole original point is that raw SQL isn't right in all situations, and you appear to be arguing that I just use SQL instead.

[ Parent | on HN ]

Re:Bye Bye Mongo, Hello Postgres by inferiorhuman on Wednesday December 19, 2018 @09:50PM (#18722118)

I can't speak to every ORM or database interface in existence but ActiveRecord will happily handle Postgres arrays and let you use the built-in array functions just handily without having to write queries by hand. Ecto is less elegant, but you can still finangle some arrays with it.

As far as views are concerned, I don't know what to tell you. Sure, you'll probably have to craft the view itself by hand. The result is that you can then use most abstractions of your choosing on top of it though.

[ Parent | on HN ]

Re:Bye Bye Mongo, Hello Postgres by bonesss on Thursday December 20, 2018 @07:08AM (#18724202)

There's also the possibility of using automation to create, update, and manage views. That lets your app be 'dynamic' with regards to new data and new datatypes, but also preserves the performance, debugging, segregation, and maintenance benefits of the underlying DB.

[ Parent | on HN ]

Re:Bye Bye Mongo, Hello Postgres by xkcd-sucks on Wednesday December 19, 2018 @09:24PM (#18722010)

>For example, can it...

Yes. There will be a subquery and jsonb indexes need to be thought out in order to make it fast

[ Parent | on HN ]

Re:Bye Bye Mongo, Hello Postgres by inferiorhuman on Wednesday December 19, 2018 @07:47PM (#18721515)

> Across all the different means of interacting with a database I have experience with (from full-fledged ORMs like ActiveRecord, to sprocs in ASP.NET), I've found that it offers the best compromise between providing an ergonomic abstraction over the database, and not hiding all of the nitty-gritty details you need to worry about in order to write performant queries or use database-specific features like triggers or window functions.

Ahh Elixir. My favorite language that really just tries so hard to shoot itself in the foot. I'm currently in the protracted process of trying to upgrade a Phoenix app to the current versions. Currently I'm at the rewrite it in Rust and try out Rocket + Diesel stage.

Diesel is... interesting and makes me long for Ecto (which is often used as an ORM although the model bits got split off into a different project).

[ Parent | on HN ]

Re:Bye Bye Mongo, Hello Postgres by inferiorhuman on Thursday December 20, 2018 @02:30AM (#18723104)

Love the downvotes instead of comments. I've walked away from Elixir as the best practice deployment methodology (Distillery) is non-op on FreeBSD[1] and has been for a few months while the Distillery author is mum. All of this despite the vast love that the Elixir community seems to heap on FreeBSD.

Erlang and Elixir have plenty of promise but there simply is no good story for production deployments. Distillery and edeliver approximate capistrano, and that sounds great when it works (although I'd just as soon skip edeliver). But when it doesn't I'd much rather dig into the mess of ruby that is Capistrano than the mess of shell scripts, erlang, and god knows what else goes into a Distillery release.

Elixir is a really interesting language, but Phoenix seems to still be pretty wet behind the ears and very much in flux. Ecto too to a much smaller extent.

1: Some of the distillery scripts can communicate with epmd, some just give up.

[ Parent | on HN ]