How to save changes with Breeze without EF?

Question

I'm working with repositories and one thing I'm really working hard on is to make things as most decoupled as they can. So, if tomorrow we change from relational databases to something else, like NoSQL and things like that we are good to go, we just have to change our DAL.

I've been trying to find out how to implement the SaveChanges method in my WebAPI controller without needing to use the EFContextProvider. I've found then the Breeze NoDb sample, however this sample uses the Breeze ContextProvider in the repository. This is something that troubles me because Breeze is a JS library, so it is something about the presentation of my application. In that case, making the repository use a component from Breeze will couple the DAL and the presentation, something I don't want to do.

Searching again for how to implement SaveChanges without EF I've found this question where there's one very good answer telling how to convert the SaveBundle to a SaveMap and then tell to use this to implement the saving logic. However I'm stuck in this method because the entries of the SaveMap give just one Type object and the EntityInfo, so I don't see how to use this with my repositories.

So, how to deal with SaveChanges without to refer to EFContextProvider and without coupling the repositories with the ContextProvider?

Answer 1

Are you planning to switch from SQL Server to NoSQL database? why don't you want to do that just now? How often are you planning to switch backing storage? Probably not often, if ever.

I found that database switch, especially from SQL to NoSQL is a big shift in paradigm. In one of my application I've gone through conversion from SQL to RavenDb. Despite of having everything decoupled and with using Repositories everywhere, I still had to rewrite most of the application storage logic.

What you are trying to do - you are not going to need it. So stop making life hard for yourself and get on with implementing features.

Answer 2

The ContextProvider does the work of converting the JObject (which Json.NET gives you in the SaveChanges method), into real, typed .NET objects. The EntityInfo object that the ContextProvider creates for each entity contains the entity object itself, as well as the entityAspect properties that it got from the client: the EntityState (Added, Modified, or Deleted), the original values of all changed properties, and the temporary values for any auto-generated keys. This is the information that you would need to save the entities yourself. The "SaveMap" just organizes them by Type for convenience, but you can manipulate them however you like.

As described in the post you referenced, you could proceed by using a ContextProvider just to convert the JObject to entities, then pass those entities to the appropriate repositories. Your repositories don't need to know anything about the ContextProvider.

Answer 3

Breeze offers an NHibernate provider that you can look at that shows how to talk to a non EF backend that is still a .NET server. The ContextProvider is a convenence that makes implementing any .NET provider substantially easier, but it is by no means a requirement.

As for NoSQL you should take a look at the breeze Node provider and MongoDB sample which is hosted in NodeJs ( which shows that the ContextProvider is obviously not a requirement).

We also expect to have a Breeze server implementation written in Java in the near future, which again has no "ContextProvider" requirement.