Hi all,

I’ve just published json_api_query_builder which can transform a JSON-API request with filters, fields, include, sort into an Ecto Query.

Eg:

params = %{
  "fields" => %{
    "article" => "description",
    "comment" => "body",
    "user" => "email,username"
  },
  "filter" => %{
    "articles.tag" => "animals"
  },
  "include" => "articles,articles.comments,articles.comments.user"
}

Blog.Repo.all(Blog.User.Query.build(params))

To map between the JSON-API model and the DB model, the user implements a Query module with callbacks to handle filters, field mapping, preloading relationships, etc…

defmodule Article do
  use Ecto.Schema

  schema "articles" do
    field :body, :string
    field :description, :string
    field :slug, :string
    field :tag_list, {:array, :string}
    field :title, :string
    belongs_to :author, User, foreign_key: :user_id
    has_many :comments, Comment
    timestamps()
  end

  defmodule Query do
    use JsonApiQueryBuilder,
      schema: Article,
      type: "article",
      relationships: ["author", "comments"]

    @impl JsonApiQueryBuilder
    def filter(query, "tag", value), do: from(a in query, where: ^value in a.tag_list)
    def filter(query, "comments", params) do
      comment_query = from(Comment, select: [:article_id], distinct: true) |> Comment.Query.filter(params)
      from a in query, join: c in ^subquery(comment_query), on: a.id == c.article_id
    end
    def filter(query, "author", params) do
      user_query = from(User, select: [:id]) |> User.Query.filter(params)
      from a in query, join: u in ^subquery(user_query), on: a.user_id == u.id
    end

    @impl JsonApiQueryBuilder
    def include(query, "comments", comment_params) do
      from query, preload: [comments: ^Comment.Query.build(comment_params)]
    end
    def include(query, "author", author_params) do
      from query, select_merge: [:author_id], preload: [author: ^User.Query.build(author_params)]
    end
  end
end

Links:

Hex Package
Docs
Github