We need to add folder structure to database. By discuss, * The structure of folder would just like its parent card list. * Add a "Folder" class directly that inherit from card class * Folder objects save folder ID (maybe a UUID) pointing to real folder records in database.

Hi Rex, Would you like to review the patch? Thanks

Our tests are under directory named '_test' because of the reason in https://bugzilla.mozilla.org/show_bug.cgi?id=1095219#c9 You could run them by rename '_test' to 'test' and run unit test as before.

Comment on attachment 8535502 [details] pull request Looks good to me, but we need an explicit way for whom uses Folder to flush data into DB after updating. See my comment on Github.

Comment on attachment 8535502 [details] pull request Hi Rex, I've addressed your comments. Now it will automatically write to data store every time we update folder contents. Please help to review it again, thanks

Comment on attachment 8535502 [details] pull request Well, it's generally OK but I found a few small issues. So please confirm comments on Github before landing. Some of them are suggestions that you may consider but not blocking. And also we should keep in mind that test cases are not fully covered yet. Thanks for your work!

Comment addressed, waiting for Gaia-Try result https://treeherder.mozilla.org/ui/#/jobs?repo=gaia-try&revision=f5ae4ba7ca36

Landed on master https://github.com/mozilla-b2g/gaia/commit/9259e0b236da1ae5fdb4fce0eac3e20617206534