connect options config and scenarios

[joaqcid]

trackBy: same for every action or not present
cancelPrevious: false (default value)

this.ngxsFirestoreConnect.connect(Action, {
  to: FirestoreStream,
});

this.ngxsFirestoreConnect.connect(Action, {
  to: FirestoreStream,
  trackBy: () => 'static',
  cancelPrevious: false
});

trackBy: same for every action or not present
cancelPrevious: true

this.ngxsFirestoreConnect.connect(Action, {
  to: FirestoreStream,
  cancelPrevious: true
});

this.ngxsFirestoreConnect.connect(Action, {
  to: FirestoreStream,
  trackBy: () => 'static',
  cancelPrevious: true
});

trackBy: different for every action
cancelPrevious: false (default value)

this.ngxsFirestoreConnect.connect(Action, {
  to: FirestoreStream,
  trackBy: (action) => action.payload // assumes payload is different on each dispatch,
});

this.ngxsFirestoreConnect.connect(Action, {
  to: FirestoreStream,
  trackBy: (action) => action.payload // assumes payload is different on each dispatch,
  cancelPrevious: false
});

trackBy: different for every action
cancelPrevious: true

this.ngxsFirestoreConnect.connect(Action, {
  to: FirestoreStream,
  trackBy: (action) => action.payload // assumes payload is different on each dispatch,
  cancelPrevious: true
});

---

@markwhitfeld comments:
Ok, so I'll summarise my discussions with @joaqcid in separate comments below.
Firstly, let's establish a baseline for what the connect options mean:

• trackBy: used to determine how many connections are triggered by the same action
  • setting a trackBy will allow for multiple connections, each of which is identified by the data returned by the trackBy that you provide
  • if you don't set a trackBy (the default) then there will only ever be one active connection for this action
  • similarly if you specify a constant value for the trackBy then there will only ever be one connection for this action
• cancelPrevious: used to determine how a new action will be handled
  • essentially this represents the choice of "Cancel previous connection" or "Ignore new connection"
  • if cancelPrevious is false (the default) then new actions are ignored if there is an existing connection with the same trackBy
  • if cancelPrevious is true, then the new action will be used to create a connection that will replace an existing connection with the same trackBy

The combination of these two properties fully determines how the NgxsFireStoreConnect handles its "connections" to streams. Obviously the source stream created by the action call can also have its own logic about when it completes.

Each combination of options is listed below:

• { trackBy: undefined, cancelPrevious: false, ... } connect options config and scenarios #53 (comment)
• { trackBy: undefined, cancelPrevious: true, ... } connect options config and scenarios #53 (comment)
• { trackBy: (a) => a.id, cancelPrevious: false, ... } connect options config and scenarios #53 (comment)
• { trackBy: (a) => a.id, cancelPrevious: true, ... } connect options config and scenarios #53 (comment)

[markwhitfeld]

[DEFAULT]
{ trackBy: undefined, cancelPrevious: false, ... }
Action: Get { id: string, other: string }

#	Action	Payload	Connect	Connection Count	Closed By #
1	Get	{ id: 1, other: 'a' }	Yes	1	None
2	Get	{ id: 2, other: 'a' }	Ignored	1	-
3	Get	{ id:, other: 'a' }	Ignored	1	-
4	Get	{ id:, other: 'b' }	Ignored	1	-

Final connection count = 1
Actions connected after the sequence above:
[ { id: 1, other: 'a' } ]

PS. Equivalent to rxjs exhaustMap

[markwhitfeld]

{ trackBy: undefined, cancelPrevious: true, ... }
Action: Get { id: string, other: string }

Example sequence of actions and behavior:

#	Action	Payload	Connect	Connections Count	Closed By #
1	Get	{ id: 1, other: 'a' }	Yes	1	2
2	Get	{ id: 2, other: 'a' }	Yes	1	3
3	Get	{ id: 3, other: 'a' }	Yes	1	4
4	Get	{ id: 1, other: 'b' }	Yes	1	None

Final connection count = 1
Actions connected after the sequence above:
[ { id: 1, other: 'b' } ]

PS. Equivalent to rxjs switchMap

[markwhitfeld]

{ trackBy: (a) => a.id, cancelPrevious: false, ... }
Action: Get { id: string, other: string }

Example sequence of actions and behavior:

#	Action	Payload	Connect	Connections Count	Closed By #
1	Get	{ id: 1, other: 'a' }	Yes	1	None
2	Get	{ id: 2, other: 'a' }	Yes	2	None
3	Get	{ id: 3, other: 'a' }	Yes	3	None
4	Get	{ id: 1, other: 'b' }	No	3	-

Final connection count = 3
Actions connected after the sequence above:
[ { id: 1, other: 'a' }, { id: 2, other: 'a' }, { id: 3, other: 'a' } ]

PS. Equivalent to rxjs groupBy(trackBy) then exhaustMap
or rxjs distinctUntilKeyChanged('id') and then mergeMap

[markwhitfeld]

{ trackBy: (a) => a.id, cancelPrevious: true, ... }
Action: Get { id: string, other: string }

Example sequence of actions and behavior:

#	Action	Payload	Connect	Connections Count	Closed By #
1	Get	{ id: 1, other: 'a' }	Yes	1	4
2	Get	{ id: 2, other: 'a' }	Yes	2	None
3	Get	{ id: 3, other: 'a' }	Yes	3	None
4	Get	{ id: 1, other: 'b' }	Yes	3	None

Final connection count = 3
Actions connected after the sequence above:
[ { id: 1, other: 'b' }, { id: 2, other: 'a' }, { id: 3, other: 'a' } ]

PS. Equivalent to rxjs groupBy(trackBy) then switchMap

[markwhitfeld]

Notes from discussion with @joaqcid around how to control concurrency....

• Group connections by an ID- track connection by ID
• how do we treat previous connections in the same group: cancel / prefer
• how do we handle connections from other groups?
  • keep / close others
  • maxConnections: 1
  • maxTrackedConnections: 1
  • keepPrevious
  • keepLast