geo Query replicating from ruby to Ecto Elixir - ruby

Question

In Ruby I have this function query.by_distance where as by_distance is something like
def_dataset_method(:by_distance) do |from, meters|
point = Geocoding.as_point(from)
query = "ST_DWithin(location, ST_SetSRID(ST_Point(?, ?), 4326)::geography, ?)"
where(query, point.lng, point.lat, meters)
end
in a ruby endpoint user is passing 2 values which are is_near_to which is mostly name of a city or a country.. Through which Geecoding is getting its points and 2 value is within_distance which are meters for getting cameras within this distance.
The above is happening in Ruby.
What am doing in Elixir to replicate it is
def by_distance(query, is_near_to, within_distance) do
[%{"lat" => lat, "lng" => lng}] = fetch(is_near_to)
latitude = lat
longitude = lng
query
|> where([cam], st_dwithin(cam.location, st_set_srid(st_point_from_text(^"#{latitude},#{longitude}"), 4326), ^within_distance))
end
for getting lat and long am doing something as
defmodule EvercamMedia.Geocode do
def fetch(address) do
response = HTTPotion.get "http://maps.googleapis.com/maps/api/geocode/json?address=#{URI.encode(address)}&sensor=false"
{:ok, results} = Poison.decode response.body
get_in(results, ["results", Access.all(), "geometry", "location"])
end
end
now I have same scenarios. I have both values is_near_to and within_distance. But am totally unaware of this that how I can replicate the same thing in a query as we are using geo in our project and by the docs its clearly possible but am not getting the way how to do it.

Answer 1

This is part of an app I'm working on, I believe it does what you need, it uses a fragment to pass the ST_distance_sphere call directly to postgis.
Using the library https://github.com/bryanjos/geo and postgis
In the model
def near_by(query, point, distance) do
from place in query,
where: fragment("ST_distance_sphere(?,?)", place.location, ^point) >= ^distance,
order_by: fragment("ST_distance_sphere(?,?)", place.location, ^point),
select: {place, fragment("ST_distance_sphere(?,?)", place.location, ^point)}
end
In the controller
def near_by(conn, %{"latitude" => latitude, "longitude" => longitude, "distance" => distance}) do
point = %Geo.Point{coordinates: {String.to_float(latitude), String.to_float(longitude)}, srid: 4326}
places = Place
|> Place.near_by(point, String.to_float(distance))
|> Repo.all
render(conn, "near_by.json", places: places)
end
In the view
def render("near_by_place.json", %{place: place}) do
{ place, distance } = place
{lat, lon} = place.location.coordinates
%{id: place.id,
name: place.name,
latitude: lat,
longitude: lon,
distance: distance}
end