Generic CouchDBDAO class

I cleaned up the CouchDB handling code which essentially provides a http proxy for CouchDB. since CouchDB itself is providing Restful API, this may be seen as unnecessary duplication.

But this is useful to avoid browser restriction(although there a some other techniques in Dart), and this can be used as a template to provide a restful API for other db.

One interesting aspect of current implementation is such DAO class is designed as generic class.Compared to Hibernate/JPA, this approach is very simple.

[web client]

ICouchDbClientDAO<Expense> dao = new CouchDbClientDAO<Expense>(fromMap, fromJson, toJson);

    loadButtom = new ButtonComp(this, "Load", (_) {
      dao.fetchAll().then((List<Expense> es){ table.load(es);});
    });

    newButtom = new ButtonComp(this, "New", (_) {
      Expense e = form.create();
    });
   
    saveButtom = new ButtonComp(this, "Save", (_) {
      if (form.e != null) {
        Expense e = form.save();
        // this part is tricky..
        // since e is fill from InputText, when it is an empty text, it will assign "" instead of null..
        if (e.id == "") e.id = null;
        if (e.rev == "") e.rev = null;
        ((e.id == null)?dao.insert(e):dao.update(e)).then((Expense e0){
          e.id = e0.id;
          e.rev = e0.rev;
          table.addOrUpdate(e);
        });
      }
    });
   
    deleteButtom = new ButtonComp(this, "Delete", (_) {
      Expense e = form.e;
      if (e != null) {
        dao.delete(e).then((ok){
          if (ok) {
            form.delete();
            table.delete(e);
          }
        });
      }
    });

Here, the argument of CouchDbClientDAO's constructor takes fromMap, fromJson, toJson. This is required since I have not provided Json binding library yet, these functions must be defined manually for each entity classes(e.g, Expense).

[server]

void main() {

  // register reflection factory
  initClassMirrorFactory();

  CouchDbDAO<Expense> couchDbDAO = new CouchDbDAO<Expense>(couchdb_host, couchdb_port, dbName, fromMap, toJson);
 
  CouchDbHttpServer server = new CouchDbHttpServer(couchDbDAO, fromJson, toJson);
 
  server.startHttpServer(http_server_host, http_server_port);
}

No other code are required to make such entity class persistent.