Dynamic models in the Phoenix Framework

Question

Is there a way to dynamically create and use models in Phoenix? I have an application that stores metadata about client tables: they set several fields (column names and types), and then send me CSV files for parsing and storing. From the saved metadata, I would like to create a model so that I can use Ecto to manage the client table and execute queries against it.

I come from the background of Django, where I can use the built-in ORM function type()to create models on the fly, and then use them without the need to generate migrations or other model code in the application.

In Python, I would (roughly) do:

class MetaModel(models.Model):
    table_name = models.CharField(...)
    model_name = models.CharField(...)
    field_defs = JSONField(...)

    def resolve_fields(self):
        # takes values from `field_defs` and converts them into
        # django field instances

     def get_model(self):
         class Meta:
             app_label = 'dynamic'
             db_table = self.table_name
         fields = self.resolve_fields()
         attrs = {'__module__': 'dynamic', 'Meta': Meta}
         attrs.update(fields)
         model = type(self.model_name, (models.Model,), attrs)
         return model

     def create_table(self):
         with connection.schema_editor() as se:
             model = self.get_model()
             se.create_model(model)

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Answer 1

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defmodule A do
  def go(module, table, fields) do
    Module.create(module, quote do
      use MyApp.Web, :model
      schema unquote(table) do
        unquote(for {name, type} <- fields do
          quote do
            field unquote(name), unquote(type)
          end
        end)
      end
    end, Macro.Env.location(__ENV__))
  end
end

A.go MyPost, "posts", [
  {:title, :string},
  {:content, :string},
]

# MyPost is now just like any other Schema module in Phoenix.

IO.inspect MyApp.Repo.all(MyPost)

:

[debug] QUERY OK source="posts" db=2.8ms queue=0.1ms
SELECT p0."id", p0."title", p0."content" FROM "posts" AS p0 []
[%MyPost{__meta__: #Ecto.Schema.Metadata<:loaded, "posts">,
  content: "Hello from Joe", id: 1, title: "Hello"},
 %MyPost{__meta__: #Ecto.Schema.Metadata<:loaded, "posts">,
  content: "Hello from Mike", id: 2, title: "Hello"},
 %MyPost{__meta__: #Ecto.Schema.Metadata<:loaded, "posts">,
  content: "Hello from Robert", id: 3, title: "Hello"}]