improvement: do not create snapshots for resources that have no attributes #571 (#599)

Author: horberlan

lib/migration_generator/migration_generator.ex

@@ -1983,6 +1983,17 @@ defmodule AshPostgres.MigrationGenerator do
     end)
   end
 
+  defp resource_has_meaningful_content?(snapshot) do
+    [
+      snapshot.attributes,
+      snapshot.identities,
+      snapshot.custom_indexes,
+      snapshot.custom_statements,
+      snapshot.check_constraints
+    ]
+    |> Enum.any?(&Enum.any?/1)
+  end
+
   defp do_fetch_operations(snapshot, existing_snapshot, opts, acc \\ [])
 
   defp do_fetch_operations(
@@ -1996,34 +2007,41 @@ defmodule AshPostgres.MigrationGenerator do
   end
 
   defp do_fetch_operations(snapshot, nil, opts, acc) do
-    empty_snapshot = %{
-      attributes: [],
-      identities: [],
-      schema: nil,
-      custom_indexes: [],
-      custom_statements: [],
-      check_constraints: [],
-      table: snapshot.table,
-      repo: snapshot.repo,
-      base_filter: nil,
-      empty?: true,
-      multitenancy: %{
-        attribute: nil,
-        strategy: nil,
-        global: nil
-      }
-    }
-
-    do_fetch_operations(snapshot, empty_snapshot, opts, [
-      %Operation.CreateTable{
+    if resource_has_meaningful_content?(snapshot) do
+      empty_snapshot = %{
+        attributes: [],
+        identities: [],
+        schema: nil,
+        custom_indexes: [],
+        custom_statements: [],
+        check_constraints: [],
         table: snapshot.table,
-        schema: snapshot.schema,
         repo: snapshot.repo,
-        multitenancy: snapshot.multitenancy,
-        old_multitenancy: empty_snapshot.multitenancy
+        base_filter: nil,
+        empty?: true,
+        multitenancy: %{
+          attribute: nil,
+          strategy: nil,
+          global: nil
+        }
       }
-      | acc
-    ])
+
+      do_fetch_operations(snapshot, empty_snapshot, opts, [
+        %Operation.CreateTable{
+          table: snapshot.table,
+          schema: snapshot.schema,
+          repo: snapshot.repo,
+          multitenancy: snapshot.multitenancy,
+          old_multitenancy: empty_snapshot.multitenancy
+        }
+        | acc
+      ])
+    else
+      unless opts.quiet do
+        Logger.info("Skipping migration for empty resource: #{snapshot.table} (no attributes, identities, indexes, statements, or constraints)")
+      end
+      acc
+    end
   end
 
   defp do_fetch_operations(snapshot, old_snapshot, opts, acc) do

test/migration_generator_test.exs

@@ -111,6 +111,79 @@ defmodule AshPostgres.MigrationGeneratorTest do
     end
   end
 
+  describe "empty resources" do
+    setup do
+      on_exit(fn ->
+        File.rm_rf!("test_snapshots_path")
+        File.rm_rf!("test_migration_path")
+      end)
+    end
+
+    test "empty resource does not generate migration files" do
+      defresource EmptyPost, "empty_posts" do
+        resource do
+          require_primary_key?(false)
+        end
+
+        actions do
+          defaults([:read, :create])
+        end
+      end
+
+      defdomain([EmptyPost])
+
+      AshPostgres.MigrationGenerator.generate(Domain,
+        snapshot_path: "test_snapshots_path",
+        migration_path: "test_migration_path",
+        quiet: false,
+        format: false,
+        auto_name: true
+      )
+
+      migration_files =
+        Path.wildcard("test_migration_path/**/*_migrate_resources*.exs")
+        |> Enum.reject(&String.contains?(&1, "extensions"))
+
+      assert migration_files == []
+
+      snapshot_files =
+        Path.wildcard("test_snapshots_path/**/*.json")
+        |> Enum.reject(&String.contains?(&1, "extensions"))
+
+      assert snapshot_files == []
+    end
+
+    test "resource with only primary key generates migration" do
+      defresource PostWithId, "posts_with_id" do
+        attributes do
+          uuid_primary_key(:id)
+        end
+      end
+
+      defdomain([PostWithId])
+
+      AshPostgres.MigrationGenerator.generate(Domain,
+        snapshot_path: "test_snapshots_path",
+        migration_path: "test_migration_path",
+        quiet: false,
+        format: false,
+        auto_name: true
+      )
+
+      migration_files =
+        Path.wildcard("test_migration_path/**/*_migrate_resources*.exs")
+        |> Enum.reject(&String.contains?(&1, "extensions"))
+
+      assert length(migration_files) == 1
+
+      snapshot_files =
+        Path.wildcard("test_snapshots_path/**/*.json")
+        |> Enum.reject(&String.contains?(&1, "extensions"))
+
+      assert length(snapshot_files) == 1
+    end
+  end
+
   describe "creating initial snapshots" do
     setup do
       on_exit(fn ->