Do not overwrite migrations, create new using pattern timestamp.table.json

lib/migration_generator/migration_generator.ex

@@ -309,20 +309,37 @@ defmodule AshPostgres.MigrationGenerator do
       Enum.each(snapshots, fn snapshot ->
         snapshot_binary = snapshot_to_binary(snapshot)
 
-        snapshot_file =
+        snapshot_table = "#{timestamp()}_#{snapshot.table}"
+
+        snapshot_folder =
           if tenant? do
             opts.snapshot_path
             |> Path.join(repo_name)
             |> Path.join("tenants")
-            |> Path.join(snapshot.table <> ".json")
           else
             opts.snapshot_path
             |> Path.join(repo_name)
-            |> Path.join(snapshot.table <> ".json")
           end
 
+        snapshot_file =
+          snapshot_folder
+          |> Path.join(snapshot_table <> ".json")
+
         File.mkdir_p(Path.dirname(snapshot_file))
         File.write!(snapshot_file, snapshot_binary, [])
+
+        # create a new version file to track latest migration file
+        version_file =
+          snapshot_folder
+          |> Path.join(snapshot.table <> ".version.json")
+
+        version_binary =
+          snapshot_to_binary(%{
+            latest_version: snapshot_file
+          })
+
+        File.mkdir_p(Path.dirname(version_file))
+        File.write!(version_file, version_binary, [])
       end)
     end
 
@@ -937,7 +954,21 @@ defmodule AshPostgres.MigrationGenerator do
         Path.join(opts.snapshot_path, repo_name)
       end
 
-    file = Path.join(folder, snapshot.table <> ".json")
+    # get name of latest version file.
+    version_file = Path.join(folder, snapshot.table <> ".version.json")
+
+    file =
+      if File.exists?(version_file) do
+        file_content =
+          version_file
+          |> File.read!()
+          |> Jason.decode!(keys: :atoms!)
+
+        file_content.latest_version
+      else
+        version_file = Path.join(folder, snapshot.table <> ".json")
+        version_file
+      end
 
     if File.exists?(file) do
       file

test/migration_generator_test.exs

@@ -79,16 +79,26 @@ defmodule AshPostgres.MigrationGeneratorTest do
     end
 
     test "it creates a snapshot for each resource" do
-      assert File.exists?(Path.join(["test_snapshots_path", "test_repo", "posts.json"]))
+      assert File.exists?(Path.wildcard("test_snapshots_path/test_repo/*_posts.json"))
+      assert File.exists?(Path.join(["test_snapshots_path", "test_repo", "posts.version.json"]))
     end
 
     test "the snapshots can be loaded" do
-      assert File.exists?(Path.join(["test_snapshots_path", "test_repo", "posts.json"]))
+      assert File.exists?(Path.wildcard("test_snapshots_path/test_repo/*_posts.json"))
+      assert File.exists?(Path.join(["test_snapshots_path", "test_repo", "posts.version.json"]))
     end
 
     test "the snapshots contain valid json" do
-      assert File.read!(Path.join(["test_snapshots_path", "test_repo", "posts.json"]))
+      assert File.exists?(Path.join(["test_snapshots_path", "test_repo", "posts.version.json"]))
+
+      assert File.read!(Path.wildcard("test_snapshots_path/test_repo/*_posts.json"))
              |> Jason.decode!(keys: :atoms!)
+
+      version_file_content =
+        File.read!(Path.join(["test_snapshots_path", "test_repo", "posts.version.json"]))
+        |> Jason.decode!(keys: :atoms!)
+
+      assert Map.get(version_file_content, :latest_version, nil) != nil
     end
 
     test "the migration creates the table" do