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GeoPostGIS

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Postgrex extension for the PostGIS data types. Uses the geo library

Installation

The package can be installed by adding :geo_postgis to your list of dependencies in mix.exs:

def deps do
  [
    {:geo_postgis, "~> 3.4"}
  ]
end

Make sure PostGIS extension to your database is installed. More information here

Optional Configuration

# When a binary is passed to `Geo.PostGIS.Geometry.cast/1` implementation of
# `Ecto.Type.cast/1`, it is assumed to be a GeoJSON string. When this happens,
# geo_postgis will use Poison, by default, to convert the binary to a map and
# then convert that map to one of the Geo structs. If in these cases you would
# like to use a different JSON parser, you can set the config below.

# config.exs
config :geo_postgis,
  json_library: Jason # If you want to set your JSON module

Examples

Postgrex Extension for the PostGIS data types, Geometry and Geography:

Postgrex.Types.define(MyApp.PostgresTypes, [Geo.PostGIS.Extension], [])

opts = [hostname: "localhost", username: "postgres", database: "geo_postgrex_test", types: MyApp.PostgresTypes ]
[hostname: "localhost", username: "postgres", database: "geo_postgrex_test", types: MyApp.PostgresTypes]

{:ok, pid} = Postgrex.Connection.start_link(opts)
{:ok, #PID<0.115.0>}

geo = %Geo.Point{coordinates: {30, -90}, srid: 4326}
%Geo.Point{coordinates: {30, -90}, srid: 4326}

{:ok, _} = Postgrex.Connection.query(pid, "CREATE TABLE point_test (id int, geom geometry(Point, 4326))")
{:ok, %Postgrex.Result{columns: nil, command: :create_table, num_rows: 0, rows: nil}}

{:ok, _} = Postgrex.Connection.query(pid, "INSERT INTO point_test VALUES ($1, $2)", [42, geo])
{:ok, %Postgrex.Result{columns: nil, command: :insert, num_rows: 1, rows: nil}}

Postgrex.Connection.query(pid, "SELECT * FROM point_test")
{:ok, %Postgrex.Result{columns: ["id", "geom"], command: :select, num_rows: 1,
rows: [{42, %Geo.Point{coordinates: {30.0, -90.0}, srid: 4326 }}]}}

Use with Ecto:

#If using with Ecto, you may want something like thing instead
Postgrex.Types.define(MyApp.PostgresTypes,
              [Geo.PostGIS.Extension] ++ Ecto.Adapters.Postgres.extensions(),
              json: Jason)

#Add extensions to your repo config
config :thanks, Repo,
  database: "geo_postgrex_test",
  username: "postgres",
  password: "postgres",
  hostname: "localhost",
  adapter: Ecto.Adapters.Postgres,
  types: MyApp.PostgresTypes


#Create a model
defmodule Test do
  use Ecto.Model

  schema "test" do
    field :name,           :string
    field :geom,           Geo.PostGIS.Geometry
  end
end

#Geometry or Geography columns can be created in migrations too
defmodule Repo.Migrations.Init do
  use Ecto.Migration

  def up do
    create table(:test) do
      add :name,     :string
      add :geom,     :geometry
    end
  end

  def down do
    drop table(:test)
  end
end

Ecto migrations can also use more elaborate PostGIS GIS Objects. These types are useful for enforcing constraints on {Lng,Lat} (order matters), or ensuring that a particular projection/coordinate system/format is used.

defmodule Repo.Migrations.AdvancedInit do
  use Ecto.Migration

  def up do
    create table(:test) do
      add :name,     :string
    end
    # Add a field `lng_lat_point` with type `geometry(Point,4326)`.
    # This can store a "standard GPS" (epsg4326) coordinate pair {longitude,latitude}.
    execute("SELECT AddGeometryColumn ('test','lng_lat_point',4326,'POINT',2);")

    # Once a GIS data table exceeds a few thousand rows, you will want to build an index to speed up spatial searches of the data
    # Syntax - CREATE INDEX [indexname] ON [tablename] USING GIST ( [geometryfield] );
    execute("CREATE INDEX test_geom_idx ON test USING GIST (lng_lat_point);")
  end

  def down do
    drop table(:test)
  end
end

Be sure to enable the PostGIS extension if you haven't already done so:

defmodule MyApp.Repo.Migrations.EnablePostgis do
  use Ecto.Migration

  def up do
    execute "CREATE EXTENSION IF NOT EXISTS postgis"
  end

  def down do
    execute "DROP EXTENSION IF EXISTS postgis"
  end
end

PostGIS functions can also be used in Ecto queries. Currently only the OpenGIS functions are implemented. Have a look at lib/geo_postgis.ex for the implemented functions. You can use them like:

defmodule Example do
  import Ecto.Query
  import Geo.PostGIS

  def example_query(geom) do
    query = from location in Location, limit: 5, select: st_distance(location.geom, ^geom)
    query
    |> Repo.one
  end
end

Development

After you got the dependencies via mix deps.get make sure that:

  • postgis is installed
  • your postgres user has the database "geo_postgrex_test"
  • your postgres db user can login without a password or you set the PGPASSWORD environment variable appropriately

Then you can run the tests as you are used to with mix test.

Copyright and License

Copyright (c) 2017 Bryan Joseph

Released under the MIT License, which can be found in the repository in LICENSE.