Add InteractionScope attribute.

[kegor]

Was initially reported by @mtornwall:

Startup has attribute [UseDbScope] which is used to say whether view model should be wrapped in Db.Scope or not. So [UseDbScope(false)] => not wrapped in scope and vice versa.

But the behavior of Db.Scope() is such that if there already is a scope allocated for an outer view model (or blended view model, IIRC), no new scope will be created for the nested view model. Instead it will be folded into the outer scope. However, sometimes you want to explicitly request that a new Db.Scope() be created. This could be done with new Transaction(....).Scope(() => ...)

I would like a new attribute, with options such as:

[InteractionScope(InteractionScopeMode.None)]

...

enum InteractionScopeMode {
      None = 0,
      Create = 0x1,
      Attach = 0x2 
}

Where their meaning would be:
• None => view model should not be attached to any scope
• Create only => view model should always get a new scope as above
• Attach only => view model should attach to existing scope, if any, but not create one
• Create | Attach => view model should attach to existing scope if any, otherwise create a new one

[kegor]

@mtornwall what i found here:

1. DbScopeMiddleware seems obsolete and MasterPageMiddleware is now responsible for creating a scope: https://github.com/Starcounter/Starcounter.Startup/blob/master/Starcounter.Startup/Routing/RouterServiceCollectionExtensions.cs#L29
   As i can see the app that now use [UseDbScope(false)] don't use AddDbScopeMiddleware (the same situation i saw during debug of the UserAdmin-app, during calling the pages with or without [UseDbScope(false)] only MasterPageMiddleware was called).
2. As was mentioned above now MasterPageMiddleware uses Db.Scope() for wrapping non-partial requests (and it is called from the AddRouter() by default): https://github.com/Starcounter/Starcounter.Startup/blob/master/Starcounter.Startup/Routing/Middleware/MasterPageMiddleware.cs#L29.
3. As i can understand you suggest to add InteractionScope and middleware similar to DbScopeMiddleware that will work using following logic:

• None => return next()
• Create only => return new Transaction().Scope(next)
• Attach only => return Db.Scope(next)
• Create | Attach => return something from two points above depending on Transaction.Current != null?

(I decided to clarify this without sending the code because the changes doesn't seems to be very big.)

What do you think, should we return to the manage of the transaction scoping outside the MasterPageMiddleware (with invocation by default in AddRouter()) and create(change existing DbScopeMiddleware) separate middleware for this?

I did not participate in discussions on the latest changes in this library, so it’s difficult for me to be sure of any of the solutions.

[mtornwall]

• None => return next()
• Create only => return new Transaction().Scope(next)
• Attach only => return Db.Scope(next)
• Create | Attach => return something from two points above depending on Transaction.Current != null?

Not quite what I had in mind, but maybe we can simplify it to:

• AttachOrCreate => return Db.Scope(next)
• AlwaysCreate => return new Transaction(...).Scope(next)

WDYT?

[kegor]

@mtornwall, yeah, sound good for me, thank you for clarification.
The last (but not least) question here is about adding (changing existing DbScopeMiddleware) for using this new attribute. Do you think that we should return to this approach (instead of current case with manage of the transaction scoping in the MasterPageMiddleware)?

[mtornwall]

Do you think that we should return to this approach (instead of current case with manage of the transaction scoping in the MasterPageMiddleware)?

As I understand it the transaction scope management in MasterPageMiddleware is only about whether or not the master page itself should have a scope attached. And so it doesn't affect how transaction scopes are assigned to attached view models. But this is based on the docs only, so I may be totally wrong.

Anyway, what I think we should have is:

• An attribute called InteractionScope, since this is the terminology we want to use in the future (i.e. avoid the word transaction).
• An InteractionScopeMiddleware (might just be a matter of renaming DbScopeMiddleware) that manages scope attachment.

WDYT?

[kegor]

@mtornwall, alright i agree with your guess regarding MasterPageMiddleware, and i think we can't achieve that without next 2 points. So i'll try to make some changes to check how it works.

[kegor]

We were discussing the last step which is consists of testing the newly released 0.8.0 version (https://www.nuget.org/packages/Starcounter.Startup/0.8.0) in all apps and updating them then and @mtornwall suggested to assign this action to him.