First version of dynamic command for Ecto.Migration

lib/ecto/migration.ex

@@ -147,7 +147,7 @@ defmodule Ecto.Migration do
   field type with database-specific options, you can pass atoms containing
   these options like `:"int unsigned"`, `:"time without time zone"`, etc.
 
-  ## Flushing
+  ## Executing and flushing
 
   Instructions inside of migrations are not executed immediately. Instead
   they are performed after the relevant `up`, `change`, or `down` callback
@@ -164,6 +164,10 @@ defmodule Ecto.Migration do
         ...
       end
 
+  However `flush/0` will raise if it would be called from `change` function when doing a rollback.
+  To avoid that we recommend to use `execute/2` with anonymous functions instead.
+  For more information and example usage please take a look at `execute/2` function.
+
   ## Comments
 
   Migrations where you create or alter a table support specifying table
@@ -740,7 +744,7 @@ defmodule Ecto.Migration do
   end
 
   @doc """
-  Executes arbitrary SQL or a keyword command.
+  Executes arbitrary SQL, anonymous function or a keyword command.
 
   Reversible commands can be defined by calling `execute/2`.
 
@@ -750,8 +754,9 @@ defmodule Ecto.Migration do
 
       execute create: "posts", capped: true, size: 1024
 
+      execute(fn -> repo().query!("select 'Anonymous function query …';", [], [log: :info]) end)
   """
-  def execute(command) when is_binary(command) or is_list(command) do
+  def execute(command) when is_binary(command) or is_function(command, 0) or is_list(command) do
     Runner.execute command
   end
 
@@ -766,11 +771,20 @@ defmodule Ecto.Migration do
 
   ## Examples
 
-      execute "CREATE EXTENSION postgres_fdw", "DROP EXTENSION postgres_fdw"
+      defmodule MyApp.MyMigration do
+        use Ecto.Migration
+
+        def change do
+          execute "CREATE EXTENSION postgres_fdw", "DROP EXTENSION postgres_fdw"
+          execute(&execute_up/0, &execute_down/0)
+        end
 
+        defp execute_up, do: repo().query!("select 'Up query …';", [], [log: :info])
+        defp execute_down, do: repo().query!("select 'Down query …';", [], [log: :info])
+      end
   """
-  def execute(up, down) when (is_binary(up) or is_list(up)) and
-                             (is_binary(down) or is_list(down)) do
+  def execute(up, down) when (is_binary(up) or is_function(up, 0) or is_list(up)) and
+                             (is_binary(down) or is_function(down, 0) or is_list(down)) do
     Runner.execute %Command{up: up, down: down}
   end
 

lib/ecto/migration/runner.ex

@@ -332,6 +332,11 @@ defmodule Ecto.Migration.Runner do
     log_and_execute_ddl(repo, log, command)
   end
 
+  defp log_and_execute_ddl(_repo, _log, func) when is_function(func, 0) do
+    func.()
+    :ok
+  end
+
   defp log_and_execute_ddl(repo, %{level: level, sql: sql}, command) do
     log(level, command(command))
     meta = Ecto.Adapter.lookup_meta(repo.get_dynamic_repo())

test/ecto/migrator_test.exs

@@ -110,6 +110,40 @@ defmodule Ecto.MigratorTest do
     end
   end
 
+  defmodule ExecuteOneAnonymousFunctionMigration do
+    use Ecto.Migration
+
+    require Logger
+
+    def change do
+      execute(fn -> Logger.info("This should fail on rollback.") end)
+    end
+  end
+
+  defmodule ExecuteTwoAnonymousFunctionsMigration do
+    use Ecto.Migration
+
+    require Logger
+
+    @disable_ddl_transaction true
+
+    @migrate_first "select 'This is a first part of ecto.migrate';"
+    @migrate_middle "select 'In the middle of ecto.migrate';"
+    @migrate_second "select 'This is a second part of ecto.migrate';"
+    @rollback_first "select 'This is a first part of ecto.rollback';"
+    @rollback_middle "select 'In the middle of ecto.rollback';"
+    @rollback_second "select 'This is a second part of ecto.rollback';"
+
+    def change do
+      execute(@migrate_first, @rollback_second)
+      execute(&execute_up/0, &execute_down/0)
+      execute(@migrate_second, @rollback_first)
+    end
+
+    defp execute_up, do: Logger.info(@migrate_middle)
+    defp execute_down, do: Logger.info(@rollback_middle)
+  end
+
   defmodule InvalidMigration do
     use Ecto.Migration
   end
@@ -169,7 +203,30 @@ defmodule Ecto.MigratorTest do
     """
   end
 
-  @tag :current
+  test "execute one anonymous function" do
+    module = ExecuteOneAnonymousFunctionMigration
+    num = System.unique_integer([:positive])
+    capture_log(fn -> :ok = up(TestRepo, num, module, [log: false]) end)
+    message = "no function clause matching in Ecto.Migration.Runner.command/1"
+    assert_raise(FunctionClauseError, message, fn -> down(TestRepo, num, module, [log: false]) end)
+  end
+
+  test "execute two anonymous functions" do
+    module = ExecuteTwoAnonymousFunctionsMigration
+    num = System.unique_integer([:positive])
+    args = [TestRepo, num, module, [log: :info]]
+
+    for {name, direction} <- [migrate: :up, rollback: :down] do
+      output = capture_log(fn -> :ok = apply(Ecto.Migrator, direction, args) end)
+      lines = String.split(output, "\n")
+      assert Enum.at(lines, 1) =~ "== Running #{num} #{inspect(module)}.change/0"
+      assert Enum.at(lines, 3) =~ ~s[execute "select 'This is a first part of ecto.#{name}';"]
+      assert Enum.at(lines, 5) =~ "select 'In the middle of ecto.#{name}';"
+      assert Enum.at(lines, 7) =~ ~s[execute "select 'This is a second part of ecto.#{name}';"]
+      assert Enum.at(lines, 9) =~ ~r"Migrated #{num} in \d.\ds"
+    end
+  end
+
   test "flush" do
     num = System.unique_integer([:positive])
     assert :ok == up(TestRepo, num, EmptyUpDownMigration, log: false)