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Ash Elixir•3y ago

Adding macros to `expr/1`

I'd like to add the st_* macros from GeoPostGIS to expr/1, possibly more in future. These macros do generate exactly the fragment syntax that is currently supported by expr, which is pretty nice, but they don't work as-is. Is doesn't look like it's possible currently to extend Ash.Expr, and I'm quite interested in changing that, or at least making it possible to mix in external macros in this way using the existing supporting constructs like fragment. Has there been any interest/thought up to now on this topic? https://github.com/bryanjos/geo_postgis/blob/master/lib/geo_postgis.ex

GitHub

geo_postgis/geo_postgis.ex at master · bryanjos/geo_postgis

Postrex Extension for PostGIS. Contribute to bryanjos/geo_postgis development by creating an account on GitHub.

38 Replies

\ ឵឵឵OP•3y ago

I'm doing a lot of queries with these things and it would be fantastic to be able to write stuff like

filter expr(st_within(^arg(:latlng), :geometry))

filter expr(st_within(^arg(:latlng), :geometry))

ZachDaniel•3y ago

https://github.com/ash-project/ash/issues/374

GitHub

Custom predicates & operators · Issue #374 · ash-project/ash

These would be exposed to the expression syntax in code, and can be made available over api extensions as well. I'm thinking something like this: support a custom configured list of functions t...

ZachDaniel•3y ago

This is the tracking issue for that feature in the meantime, there are some things you can do. 1. add calculations to the resources you want to use this with

calculate :st_within, :the_type, expr(fragment("...", ^arg(:latlng), :geometry)) do
  argument :ltlng, :type, allow_nil?: false
end

calculate :st_within, :the_type, expr(fragment("...", ^arg(:latlng), :geometry)) do
  argument :ltlng, :type, allow_nil?: false
end

2. write macros and use them in your exprs. This exact strategy may or may not work but I'm pretty sure we can make something similar to it work at least.

# in YourModule
defmacro st_within(latlng, type) do
  quote do
    st_within(^arg(:latlng), :geometry)
  end
end

# in your resources
import YourModule
expr(^st_within(latlng, type))

# in YourModule
defmacro st_within(latlng, type) do
  quote do
    st_within(^arg(:latlng), :geometry)
  end
end

# in your resources
import YourModule
expr(^st_within(latlng, type))

\ ឵឵឵OP•3y ago

Great that it's on the list Tried the second example, getting

undefined function fragment/3 (there is no such import)

undefined function fragment/3 (there is no such import)

On the plus side, if we can get that working, then I can make them understand the arg(_) -> {:_arg, _} and friends stuff, so I can write wrappers for these that can be mixed with the usual Ash stuff to some degree.

ZachDaniel•3y ago

Actually, try this

defmacro st_within(latlng, type) do
  quote do
    import Ash.Expr
    import Ash.Filter.TemplateHelpers

    expr(fragment("..", ...))
  end
end

defmacro st_within(latlng, type) do
  quote do
    import Ash.Expr
    import Ash.Filter.TemplateHelpers

    expr(fragment("..", ...))
  end
end

And if that doesn't work try it without the wrappers

\ ឵឵឵OP•3y ago

Works:

      filter expr(fragment("ST_Within(?,?)", ^arg(:latlng), :geometry))

      filter expr(fragment("ST_Within(?,?)", ^arg(:latlng), :geometry))

Not happy:

defmodule AshGeoPostgis do
  defmacro st_within(arg, attr) do
    quote do
      import Ash.Expr
      import Ash.Filter.TemplateHelpers

      fragment("ST_Within(?,?)", ^arg(unquote(arg)), unquote(attr))
    end
  end
end

defmodule AshGeoPostgis do
  defmacro st_within(arg, attr) do
    quote do
      import Ash.Expr
      import Ash.Filter.TemplateHelpers

      fragment("ST_Within(?,?)", ^arg(unquote(arg)), unquote(attr))
    end
  end
end

      filter expr(^st_within(:latlng, :geometry))

      filter expr(^st_within(:latlng, :geometry))

ZachDaniel•3y ago

whats the error?

\ ឵឵឵OP•3y ago

Same

ZachDaniel•3y ago

defmodule AshGeoPostgis do
  defmacro st_within(arg, attr) do
    quote do
      import Ash.Expr
      import Ash.Filter.TemplateHelpers

      expr(fragment("ST_Within(?,?)", ^arg(unquote(arg)), unquote(attr)))
    end
  end
end

defmodule AshGeoPostgis do
  defmacro st_within(arg, attr) do
    quote do
      import Ash.Expr
      import Ash.Filter.TemplateHelpers

      expr(fragment("ST_Within(?,?)", ^arg(unquote(arg)), unquote(attr)))
    end
  end
end

Need to wrap it in expr/1 Also if you do it that way it should just "pass through" arg stuff

defmodule AshGeoPostgis do
  defmacro st_within(a, b) do
    quote do
      import Ash.Expr
      import Ash.Filter.TemplateHelpers

      expr(fragment("ST_Within(?,?)", unquote(a), unquote(b)))
    end
  end
end

defmodule AshGeoPostgis do
  defmacro st_within(a, b) do
    quote do
      import Ash.Expr
      import Ash.Filter.TemplateHelpers

      expr(fragment("ST_Within(?,?)", unquote(a), unquote(b)))
    end
  end
end

Then you can st_within(^arg(:foo), :bar)

\ ឵឵឵OP•3y ago

Aye, that looks right. Will give it a shot when I'm back at my desk. Some progress:

defmodule AshGeoPostgis do
  defmacro st_within(contained, container) do
    quote do
      expr(fragment("ST_Within(ST_PointFromText(?),?)", unquote(contained), unquote(container)))
    end
  end
end

defmodule AshGeoPostgis do
  defmacro st_within(contained, container) do
    quote do
      expr(fragment("ST_Within(ST_PointFromText(?),?)", unquote(contained), unquote(container)))
    end
  end
end

      filter expr(^st_within(^arg(:latlng), geometry))

      filter expr(^st_within(^arg(:latlng), geometry))

ZachDaniel•3y ago

Nice! So that works?

\ ឵឵឵OP•3y ago

Yep, got input types working as well 🙂 Nested fragments working, seems good. Got a bunch of stuff to write with this over the next days for a stress test. If all goes well, I'll find some time next week to roll ash_geo_postgis. One odd thing: cast_input is not getting called for the argument type in a create with set_attribute, but is getting called when doing a read with filter expr(...).

defmodule Thing do
  use Ash.Resource, data_layer: AshPostgres.DataLayer

  attributes do
    attribute :area, :geometry
  end

  actions do
    default_actions [:read, :destroy]

    create :create do
      primary? true
      argument :area, :geo_json
      change set_attribute(:area, arg(:area))
    end

    read :containing do
      argument :point, :geo_json
      filter expr(^st_within(^arg(:point), area))
    end
  end
end

defmodule Thing do
  use Ash.Resource, data_layer: AshPostgres.DataLayer

  attributes do
    attribute :area, :geometry
  end

  actions do
    default_actions [:read, :destroy]

    create :create do
      primary? true
      argument :area, :geo_json
      change set_attribute(:area, arg(:area))
    end

    read :containing do
      argument :point, :geo_json
      filter expr(^st_within(^arg(:point), area))
    end
  end
end

Call flow for read/filter expr(...) goes: 1. :geo_json.cast_input 2. :geometry.cast_stored Call flow for create/set_attribute on the other hand: 1. :geometry.cast_input 2. :geometry.dump_to_native Because there are multiple input formats that should all be parsed into a geometry and I'd like to let them be specified explicitly, this is not ideal, but I can try to work with the current behaviour, just wanted to check if this is as intended, or is an Ash fix. (ideal would be that cast_input for the input type always gets called for an argument)

ZachDaniel•3y ago

🤔 if you could make a test showing an example of not calling cast_input when providing input for pretty much any argument anywhere, then it is almost certainly a bug 🙂 There are some cases where we don't call apply_constraints/2 (specifically when building queries)

\ ឵឵឵OP•3y ago

In this case, cast_input is getting called, but only on the underlying type (:geometry), not the input type (:geo_json), which seems wrong to me.

ZachDaniel•3y ago

So do you have :geo_json set up as a type alias somewhere I assume? like w/ the custom short names config?

\ ឵឵឵OP•3y ago

Correct

ZachDaniel•3y ago

gotcha. In that case that sounds like a bug 🙂

\ ឵឵឵OP•3y ago

Yeah changeset.ex has the cast to underlying in force_change_attribute but didn't see the input cast anywhere there or in the set_sttribute built-in.

ZachDaniel•3y ago

well the set_attribute builtin calls force_change_attribute under the hood the problem is in the action argument casting I imagine

\ ឵឵឵OP•3y ago

Yeah I know, but it's only casting to the underlying type, not from the input type

ZachDaniel•3y ago

Yeah, that makes sense arguments get casted up-front

\ ឵឵឵OP•3y ago

Right, so that's what I was thinking, maybe this is supposed to be happening further up the request chain. Where is it supposed to be getting casted?

ZachDaniel•3y ago

it happens in set_argument/3 its interesting...I think I might see the problem maybe. Can I see how you're calling the action?

\ ឵឵឵OP•3y ago

  code_interface do
    define :create
    define :containing, args: [:point]
  end

  code_interface do
    define :create
    define :containing, args: [:point]
  end

ZachDaniel•3y ago

okay yeah nvm them um....how sure are you that its not calling the function you want it to call?

\ ឵឵឵OP•3y ago

create one is bare

ZachDaniel•3y ago

just want to check our bases are you like inspecting something in the cast_input function of your types?

\ ឵឵឵OP•3y ago

Reasonably sure... I have dbg breaks on all my cast_inputs for the type wrappers.

ZachDaniel•3y ago

and you definitely have your short names configured properly?

\ ឵឵឵OP•3y ago

Same short names and same breaks are being used to validate the flow for the read action where it's working. I don't have a break on the :error catch-all but if it's getting an error out of cast and passing it through anyways, that's a bug as well.

ZachDaniel•3y ago

true, but lets check it just to be sure 😄

\ ឵឵឵OP•3y ago

Back at desk in 5

ZachDaniel•3y ago

Also try out just this Resource |> Ash.Changeset.for_action(:create, %{...input}) it should cast the arguments there w/o even calling the action

\ ឵឵឵OP•3y ago

Yep, Thing |> Ash.Changeset.for_action(:create, %{area: %{}}) triggers :geojson.cast_input correctly. And... So does the code interface call now.

ZachDaniel•2y ago

🤔

\ ឵឵឵OP•2y ago

:thinkies:

abeeshake456•2y ago

When using ash_geo library, I get

lib/companies_reg_ex/resources/recruiters.ex:37: function expr/1 imported from both Ash.Filter.TemplateHelpers and Ash.Expr, call is ambiguous
    (spark 1.1.22) expanding macro: Spark.Dsl.Extension.set_entity_opt/4
    lib/companies_reg_ex/resources/recruiters.ex:37: CompaniesRegEx.Resources.Recruiters (module)
    (ash 2.13.2) expanding macro: Ash.Resource.Dsl.Actions.Read.Options.filter/1

lib/companies_reg_ex/resources/recruiters.ex:37: function expr/1 imported from both Ash.Filter.TemplateHelpers and Ash.Expr, call is ambiguous
    (spark 1.1.22) expanding macro: Spark.Dsl.Extension.set_entity_opt/4
    lib/companies_reg_ex/resources/recruiters.ex:37: CompaniesRegEx.Resources.Recruiters (module)
    (ash 2.13.2) expanding macro: Ash.Resource.Dsl.Actions.Read.Options.filter/1

the docs for ash_geo and ash are sparse around expr. @\ ឵឵឵

\ ឵឵឵OP•2y ago

Fixes to outdated example in the readme and updates to test suite for latest ash and ash_postgres are up now on Hex ash_geo v0.1.3.

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