Add Ecto.Migration.remove_if_exists/1 (#624)

.formatter.exs

@@ -19,6 +19,7 @@ locals_without_parens = [
   remove: 1,
   remove: 2,
   remove: 3,
+  remove_if_exists: 1,
   remove_if_exists: 2,
   rename: 2,
   rename: 3,

lib/ecto/adapter/migration.ex

@@ -39,7 +39,8 @@ defmodule Ecto.Adapter.Migration do
           | {:remove, field :: atom, type :: Ecto.Type.t() | Reference.t() | binary(),
              Keyword.t()}
           | {:remove, field :: atom}
-          | {:remove_if_exists, type :: Ecto.Type.t() | Reference.t() | binary()}
+          | {:remove_if_exists, field :: atom, type :: Ecto.Type.t() | Reference.t() | binary()}
+          | {:remove_if_exists, field :: atom}
 
   @typedoc """
   A struct that represents a table or index in a database schema.

lib/ecto/adapters/myxql/connection.ex

@@ -1239,7 +1239,10 @@ if Code.ensure_loaded?(MyXQL) do
       [drop_constraint_if_exists_expr(ref, table, name), "DROP IF EXISTS ", quote_name(name)]
     end
 
-    defp column_change(_table, {:remove_if_exists, name, _type}),
+    defp column_change(table, {:remove_if_exists, name, _type}),
+      do: column_change(table, {:remove_if_exists, name})
+
+    defp column_change(_table, {:remove_if_exists, name}),
       do: ["DROP IF EXISTS ", quote_name(name)]
 
     defp column_options(opts) do

lib/ecto/adapters/postgres/connection.ex

@@ -1588,7 +1588,10 @@ if Code.ensure_loaded?(Postgrex) do
       ]
     end
 
-    defp column_change(_table, {:remove_if_exists, name, _type}),
+    defp column_change(table, {:remove_if_exists, name, _type}),
+      do: column_change(table, {:remove_if_exists, name})
+
+    defp column_change(_table, {:remove_if_exists, name}),
       do: ["DROP COLUMN IF EXISTS ", quote_name(name)]
 
     defp modify_null(name, opts) do

lib/ecto/adapters/tds/connection.ex

@@ -1470,10 +1470,13 @@ if Code.ensure_loaded?(Tds) do
     defp column_change(statement_prefix, _table, {:remove, name, _type, _opts}),
       do: [statement_prefix, "DROP COLUMN ", quote_name(name)]
 
+    defp column_change(statement_prefix, table, {:remove_if_exists, column_name, _}),
+      do: column_change(statement_prefix, table, {:remove_if_exists, column_name})
+
     defp column_change(
            statement_prefix,
            %{name: table, prefix: prefix},
-           {:remove_if_exists, column_name, _}
+           {:remove_if_exists, column_name}
          ) do
       [
         [

lib/ecto/migration.ex

@@ -1358,15 +1358,32 @@ defmodule Ecto.Migration do
   end
 
   @doc """
-  Removes a column only if the column exists when altering the constraint if the reference type is passed
-  once it only has the constraint name on reference structure.
+  Removes a column if the column exists.
 
-  This command is not reversible as Ecto does not know about column existence before the removal attempt.
+  This command is not reversible as Ecto does not know whether or not the column existed before the removal attempt.
 
   ## Examples
 
       alter table("posts") do
-        remove_if_exists :title, :string
+        remove_if_exists :title
+      end
+
+  """
+  def remove_if_exists(column) when is_atom(column) do
+    Runner.subcommand({:remove_if_exists, column})
+  end
+
+  @doc """
+  Removes a column if the column exists.
+
+  If the type is a reference, removes the foreign key constraint for the reference first, if it exists.
+
+  This command is not reversible as Ecto does not know whether or not the column existed before the removal attempt.
+
+  ## Examples
+
+      alter table("posts") do
+        remove_if_exists :author_id, references(:authors)
       end
 
   """

test/ecto/adapters/myxql_test.exs

@@ -1987,6 +1987,7 @@ defmodule Ecto.Adapters.MyXQLTest do
          {:remove, :body, :text, []},
          {:remove, :space_id, %Reference{table: :author}, []},
          {:remove_if_exists, :body, :text},
+         {:remove_if_exists, :body},
          {:remove_if_exists, :space_id, %Reference{table: :author}}
        ]}
 
@@ -2015,6 +2016,7 @@ defmodule Ecto.Adapters.MyXQLTest do
              DROP FOREIGN KEY `posts_space_id_fkey`,
              DROP `space_id`,
              DROP IF EXISTS `body`,
+             DROP IF EXISTS `body`,
              DROP FOREIGN KEY IF EXISTS `posts_space_id_fkey`,
              DROP IF EXISTS `space_id`
              """

test/ecto/adapters/postgres_test.exs

@@ -2503,6 +2503,7 @@ defmodule Ecto.Adapters.PostgresTest do
          {:remove, :body, :text, []},
          {:remove, :space_id, %Reference{table: :author}, []},
          {:remove_if_exists, :body, :text},
+         {:remove_if_exists, :body},
          {:remove_if_exists, :space_id, %Reference{table: :author}}
        ]}
 
@@ -2541,6 +2542,7 @@ defmodule Ecto.Adapters.PostgresTest do
              DROP CONSTRAINT "posts_space_id_fkey",
              DROP COLUMN "space_id",
              DROP COLUMN IF EXISTS "body",
+             DROP COLUMN IF EXISTS "body",
              DROP CONSTRAINT IF EXISTS "posts_space_id_fkey",
              DROP COLUMN IF EXISTS "space_id"
              """

test/ecto/migration_test.exs

@@ -469,6 +469,7 @@ defmodule Ecto.MigrationTest do
         remove :views
         remove :status, :string
         remove_if_exists :status, :string
+        remove_if_exists :status
       end
 
       flush()
@@ -481,7 +482,8 @@ defmodule Ecto.MigrationTest do
                   {:modify, :title, :text, []},
                   {:remove, :views},
                   {:remove, :status, :string, []},
-                  {:remove_if_exists, :status, :string}
+                  {:remove_if_exists, :status, :string},
+                  {:remove_if_exists, :status}
                 ]}
     end