Unable to add support for ST_ClosestPoint

[Aditya Sanka]

Hi @bryanjos, thanks for the awesome library. I am trying to add a macro to lib/geo/postgis.ex to support ST_ClosestPoint

defmacro st_closestpoint(geometryA, geometryB) do
      quote do: fragment("ST_ClosestPoint(?,?)", unquote(geometryA), unquote(geometryB))
end

I receive the following error while trying to use it with my queries

iex > alias StoreRoom.{Repo, BusStop, Route}
iex > import Ecto.Query
iex > import Geo.PostGIS
iex > home = %Geo.Point{coordinates: {****, ****}, srid: 4326}
iex > query = from r in Route, order_by: st_distance(r.line, ^home), distinct: r.code, limit: 5, select: r
iex > (from r in subquery(query), select: %{pickup: st_closestpoint(r.line, ^home)}) |> Repo.all()
** (Postgrex.Error) ERROR 42883 (undefined_function): function st_closestpoint(geography, unknown) does not exist
[debug] QUERY ERROR db=1.9ms
SELECT ST_ClosestPoint(s0."line",$1) FROM (SELECT DISTINCT ON (r0."code") r0."id" AS "id", r0."org" AS "org", r0."code" AS "code", r0."name" AS "name", r0."line" AS "line", r0."inserted_at" AS "inserted_at", r0."updated_at" AS "updated_at" FROM "routes" AS r0 ORDER BY r0."code", ST_Distance(r0."line",$2) LIMIT 5) AS s0 [%Geo.Point{coordinates: {78.3762, 17.4474}, srid: 4326}, %Geo.Point{coordinates: {78.3762, 17.4474}, srid: 4326}]
    (ecto) lib/ecto/adapters/sql.ex:436: Ecto.Adapters.SQL.execute_and_cache/7
    (ecto) lib/ecto/repo/queryable.ex:130: Ecto.Repo.Queryable.execute/5
    (ecto) lib/ecto/repo/queryable.ex:35: Ecto.Repo.Queryable.all/4

I am fairly new to elixir and postgis. Forgive me if this is a trivial mistake. Any guidance would of great help

[Bryan Joseph]

Everything looks right there as far as I can tell. Only thing I can think of is make sure the Postgrex types are set up. Do you get a similar error with st_distance in your query? Also maybe check that you have the postgis extension installed in postgres.

[Aditya Sanka]

Hi @bryanjos, thank you for the quick reply. The postgis extension is installed and has been enabled for this database.

I verified this by using st_distance

iex(6)> (from r in subquery(query), select: %{distance: st_distance(r.line, ^home)}) |> Repo.all()
[debug] QUERY OK db=249.8ms
SELECT ST_Distance(s0."line",$1) FROM (SELECT DISTINCT ON (r0."code") r0."id" AS "id", r0."org" AS "org", r0."code" AS "code", r0."name" AS "name", r0."line" AS "line", r0."inserted_at" AS "inserted_at", r0."updated_at" AS "updated_at" FROM "routes" AS r0 ORDER BY r0."code", ST_Distance(r0."line",$2) LIMIT 5) AS s0 [%Geo.Point{coordinates: {78.3762, 17.4474}, srid: 4326}, %Geo.Point{coordinates: {78.3762, 17.4474}, srid: 4326}]
[%{distance: 1097.178381035}, %{distance: 182.273171646},
 %{distance: 2809.06654445}, %{distance: 171.211571728},
 %{distance: 4322.601294866}]

I have also have the Postgrex types setup using

# define custom postgres types
Postgrex.Types.define(StoreRoom.PostgresTypes,
              [Geo.PostGIS.Extension] ++ Ecto.Adapters.Postgres.extensions(),
              json: Poison)

I went ahead changed the above macro to the following, to check if issue is with "ST_ClosestPoint"

# custom macros
    defmacro st_closestpoint(geometryA, geometryB) do
      quote do: fragment("ST_Distance(?,?)", unquote(geometryA), unquote(geometryB))
    end

Everything worked fine with the following query

iex(9)> (from r in subquery(query), select: %{distance1: st_distance(r.line, ^home), distance2: st_closestpoint(r.line, ^home)}) |> Repo.all()
[debug] QUERY OK db=59.6ms
SELECT ST_Distance(s0."line",$1), ST_Distance(s0."line",$2) FROM (SELECT DISTINCT ON (r0."code") r0."id" AS "id", r0."org" AS "org", r0."code" AS "code", r0."name" AS "name", r0."line" AS "line", r0."inserted_at" AS "inserted_at", r0."updated_at" AS "updated_at" FROM "routes" AS r0 ORDER BY r0."code", ST_Distance(r0."line",$3) LIMIT 5) AS s0 [%Geo.Point{coordinates: {78.3762, 17.4474}, srid: 4326}, %Geo.Point{coordinates: {78.3762, 17.4474}, srid: 4326}, %Geo.Point{coordinates: {78.3762, 17.4474}, srid: 4326}]
[%{distance1: 1097.178381035, distance2: 1097.178381035},
 %{distance1: 182.273171646, distance2: 182.273171646},
 %{distance1: 2809.06654445, distance2: 2809.06654445},
 %{distance1: 171.211571728, distance2: 171.211571728},
 %{distance1: 4322.601294866, distance2: 4322.601294866}]

I am unable to figure out the issue with "ST_ClosestPoint". I need to add a few other helper macros as well. Please point me in the right direction. Thanks in advance

[Bryan Joseph]

Sounds like maybe it could be that the function isn't defined in postgis. Try doing a normal sql query with that function and see if you get a similar error

[Aditya Sanka]

Hi @bryanjos,

I was using the type geography while declaring schema for my tables. ST_ClosestPoint only works with geometry

create table(:routes, primary_key: false) do
      add :id, :binary_id, primary_key: true
      add :org, :string
      add :code, :string
      add :name, :string
      add :line, :geometry

      timestamps()
end

Thanks Bryan.