Ecto field descriptions

thmsmlr

Hey y’all so i’m working on a project that takes in Ecto schema and generates JSONSchemas for them. Part of the project requires that the user be able to document descriptions on the ecto fields so I can put them in the JSONSchema.

I’ve done some splunking and I’m stuck. I was wondering if y’all could point me in the right direction.

I was thinking of leveraging something like module docs, or somehow retrieving the extra field opts at runtime. I’ve looked at the Ecto.Schema.field/4 source code and can’t find any leads there. Similarly it seems like the @doc attribute can only be defined at the module level.

Ideally I’d like to provide a code experience something like this.

defmodule SpamPredicition do
  use Ecto.Schema

  @primary_key false
  schema "predictions" do

    @doc "I think ideally i'd put field descriptions as @doc attributes"
    field(:class, Ecto.Enum, values: [:spam, :not_spam])

    field(:reason, :string, description: "But I could tolerate field descriptions here")
    field(:confidence_score, :float)
  end
end

Any ideas? Maybe there’s a better approach that’s easier to implement?

5 comments

#ecto #macros

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2023-12-30 11:38:35 UTC

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mayel

All I know of are comments you can add in migrations, but not sure that meets your need: Ecto.Migration — Ecto SQL v3.14.0

Post #1

mayel

I found this example to add descriptions to struct fields: TypedStruct.Plugin — TypedStruct v0.3.0 and while it doesn’t seem like the ecto fork of that library supports plugins: typed_ecto_schema v0.4.3 — Documentation this seems like a potential path forward.

Post #2

brettbeatty

From the Ecto.Schema docs I don’t see a great way to do something like this.

If you wanted a solution that would get you close for not a whole lot of effort, you could create a module attribute for field docs that accumulate across the module then do with them what you will in a before_compile. To keep these simple you’d have to include the field names in the module attribute to link them without messing with the calls to field/3.

defmodule SpamPredicition do
  use Ecto.Schema
  @before_compile MyLib

  @primary_key false
  schema "predictions" do

    @field_doc class: "I think ideally i'd put field descriptions as @doc attributes"
    field(:class, Ecto.Enum, values: [:spam, :not_spam])

    @field_doc reason: "But I could tolerate field descriptions here"
    field(:reason, :string)
    field(:confidence_score, :float)
  end
end

Killing the need to include the field name in the module attribute would be a bit harder. You could potentially create your own field/3, belongs_to/3, has_many/3, etc. macros that took the current module attr, let’s again call @field_doc, and translate it to an accumulating module attr, let’s call @field_doc_acc, before falling back to the wrapped Ecto.Schema macro.

Post #3

thmsmlr

These are great suggestions. In my particularly usecase I found an easier way to go about it.

I’m working on the GitHub - thmsmlr/instructor_ex: Structured outputs for LLMs in Elixir · GitHub library and the JSONSchema is getting sent into an LLM. What I realized is that the LLM should be resilient to whether the description is at the schema level or the field level. So I decided to just do something like,

defmodule SpamPredicition do
  use Ecto.Schema
  use Instructor.Validator

  @doc """
  ## Field Descriptions:
  - class: Whether or not the email is spam
  - reason: A short, less than 10 word rationalization for the classification
  - score: A confidence score between 0.0 and 1.0 for the classification
  """
  @primary_key false
  embedded_schema do
    field(:class, Ecto.Enum, values: [:spam, :not_spam])
    field(:reason, :string)
    field(:score, :float)
  end

In some sense, for my usecase, this is even more flexible because you can write whatever you want about the semantics of this schema in the schema level @doc and the AI can make the appropriate associations, since you know.. it’s AI or whatnot.

If I come back to this under other circumstances i’ll definitely explore these solutions. Thanks y’all for your help!

Post #4