Permit attaching files to new records

Closes #31164.

3 files changed, 53 insertions, 5 deletions

diff --git a/activestorage/lib/active_storage/attached/many.rb b/activestorage/lib/active_storage/attached/many.rb
index 0b3400bccf..6eace65b79 100644
--- a/activestorage/lib/active_storage/attached/many.rb
+++ b/activestorage/lib/active_storage/attached/many.rb
@@ -20,7 +20,11 @@ module ActiveStorage
     #   document.images.attach([ first_blob, second_blob ])
     def attach(*attachables)
       attachables.flatten.collect do |attachable|
-        attachments.create!(name: name, blob: create_blob_from(attachable))
+        if record.new_record?
+          attachments.build(record: record, blob: create_blob_from(attachable))
+        else
+          attachments.create!(record: record, blob: create_blob_from(attachable))
+        end
       end
     end
 
diff --git a/activestorage/lib/active_storage/attached/one.rb b/activestorage/lib/active_storage/attached/one.rb
index 7092f6b109..0244232b2c 100644
--- a/activestorage/lib/active_storage/attached/one.rb
+++ b/activestorage/lib/active_storage/attached/one.rb
@@ -23,7 +23,7 @@ module ActiveStorage
       if attached? && dependent == :purge_later
         replace attachable
       else
-        write_attachment create_attachment_from(attachable)
+        write_attachment build_attachment_from(attachable)
       end
     end
 
@@ -67,13 +67,13 @@ module ActiveStorage
         blob.tap do
           transaction do
             detach
-            write_attachment create_attachment_from(attachable)
+            write_attachment build_attachment_from(attachable)
           end
         end.purge_later
       end
 
-      def create_attachment_from(attachable)
-        ActiveStorage::Attachment.create!(record: record, name: name, blob: create_blob_from(attachable))
+      def build_attachment_from(attachable)
+        ActiveStorage::Attachment.new(record: record, name: name, blob: create_blob_from(attachable))
       end
 
       def write_attachment(attachment)
diff --git a/activestorage/test/models/attachments_test.rb b/activestorage/test/models/attachments_test.rb
index 23533ece1e..edd68d3051 100644
--- a/activestorage/test/models/attachments_test.rb
+++ b/activestorage/test/models/attachments_test.rb
@@ -56,6 +56,26 @@ class ActiveStorage::AttachmentsTest < ActiveSupport::TestCase
     assert ActiveStorage::Blob.service.exist?(@user.avatar.key)
   end
 
+  test "attach blob to new record" do
+    user = User.new(name: "Jason")
+
+    assert_no_changes -> { user.new_record? } do
+      assert_no_difference -> { ActiveStorage::Attachment.count } do
+        user.avatar.attach create_blob(filename: "funky.jpg")
+      end
+    end
+
+    assert user.avatar.attached?
+    assert_equal "funky.jpg", user.avatar.filename.to_s
+
+    assert_difference -> { ActiveStorage::Attachment.count }, +1 do
+      user.save!
+    end
+
+    assert user.reload.avatar.attached?
+    assert_equal "funky.jpg", user.avatar.filename.to_s
+  end
+
   test "access underlying associations of new blob" do
     @user.avatar.attach create_blob(filename: "funky.jpg")
     assert_equal @user, @user.avatar_attachment.record
@@ -160,6 +180,30 @@ class ActiveStorage::AttachmentsTest < ActiveSupport::TestCase
     assert_equal "country.jpg", @user.highlights.second.filename.to_s
   end
 
+  test "attach blobs to new record" do
+    user = User.new(name: "Jason")
+
+    assert_no_changes -> { user.new_record? } do
+      assert_no_difference -> { ActiveStorage::Attachment.count } do
+        user.highlights.attach(
+          { io: StringIO.new("STUFF"), filename: "town.jpg", content_type: "image/jpg" },
+          { io: StringIO.new("IT"), filename: "country.jpg", content_type: "image/jpg" })
+      end
+    end
+
+    assert user.highlights.attached?
+    assert_equal "town.jpg", user.highlights.first.filename.to_s
+    assert_equal "country.jpg", user.highlights.second.filename.to_s
+
+    assert_difference -> { ActiveStorage::Attachment.count }, +2 do
+      user.save!
+    end
+
+    assert user.reload.highlights.attached?
+    assert_equal "town.jpg", user.highlights.first.filename.to_s
+    assert_equal "country.jpg", user.highlights.second.filename.to_s
+  end
+
   test "find attached blobs" do
     @user.highlights.attach(
       { io: StringIO.new("STUFF"), filename: "town.jpg", content_type: "image/jpg" },