Add support for collations in Postgres

Author: Zurga

integration_test/sql/migration.exs

@@ -463,6 +463,21 @@ defmodule Ecto.Integration.MigrationTest do
     end
   end
 
+  
+  defmodule CollateMigration do
+    use Ecto.Migration
+
+    def change do
+      create table(:collate) do
+        add :string, :string, collation: "POSIX"
+        add :char, :char, collation: "POSIX"
+        add :varchar, :varchar, collation: "POSIX"
+        add :text, :text, collation: "POSIX"
+        add :integer, :integer, collation: "POSIX"
+      end
+    end
+  end
+
   import Ecto.Query, only: [from: 2]
   import Ecto.Migrator, only: [up: 4, down: 4]
 
@@ -683,4 +698,30 @@ defmodule Ecto.Integration.MigrationTest do
 
     :ok = down(PoolRepo, num, OnDeleteNilifyColumnsMigration, log: false)
   end
+
+  @tag :add_column
+  test "collate can set on a column", %{migration_number: num} do
+    assert :ok = up(PoolRepo, num, CollateMigration, log: true)
+      query = fn column -> """
+      SELECT column_name, data_type, collation_name
+      FROM information_schema.columns
+      WHERE table_name = 'collate' AND column_name = '#{column}';
+    """
+    end
+    for type <- ~w/string varchar/ do
+      assert %{
+        rows: [[^type, "character varying", "POSIX"]]
+      } = Ecto.Adapters.SQL.query!(PoolRepo, query.(type)  , [])
+    end
+      assert %{
+        rows: [["char", "character", "POSIX"]]
+      } = Ecto.Adapters.SQL.query!(PoolRepo, query.("char")  , [])
+
+    assert %{
+      rows: [["text", "text", "POSIX"]]
+    } = Ecto.Adapters.SQL.query!(PoolRepo, query.("text")  , [])
+    assert %{
+      rows: [["integer", "integer", nil]]
+    } = Ecto.Adapters.SQL.query!(PoolRepo, query.("integer")  , [])
+  end
 end

lib/ecto/adapters/postgres/connection.ex

@@ -1624,14 +1624,22 @@ if Code.ensure_loaded?(Postgrex) do
     defp column_options(type, opts) do
       default = Keyword.fetch(opts, :default)
       null = Keyword.get(opts, :null)
+      collation = Keyword.fetch(opts, :collation)
 
-      [default_expr(default, type), null_expr(null)]
+      [default_expr(default, type), null_expr(null), collation(collation, type)]
     end
 
     defp null_expr(false), do: " NOT NULL"
     defp null_expr(true), do: " NULL"
     defp null_expr(_), do: []
 
+    def collation({:ok, collation_name}, text_type)
+        when text_type in ~w/string text char varchar/a do
+      " COLLATE \"#{collation_name}\""
+    end
+
+    def collation(_, _), do: []
+
     defp new_constraint_expr(%Constraint{check: check} = constraint) when is_binary(check) do
       [
         "CONSTRAINT ",