state snapshot

[ghetolay]

Sometimes we need to simply access the current state and not react to it.
To do so, we still have to use observable like :

this.store.select( selector )
  .take(1)
  .subscribe( ... );

or in effects :

this.actions$
  .withLatestFrom( this.store.select( selector ) )

But it really seems like doing complicated things to achieve a simple task.
Would it be really bad if we could access the state directly ??

I've created an hacky getStateSnapshot( selector ) in some of my effects to experiment and didn't come into any trouble yet.

[fxck]

The thing is.. usually when you need a state snapshot, you are doing something "wrong". So what is the use case here?

There used to be getState(), getValue(), and value, but it was removed, so yeah, currently the only way is to do a subscribe.

[ghetolay]

You're scaring me, I'm doing this a lot on effects !!.

Usually when my actions refer to an entity in my state the payload is the entity id like :

SelectItemAction(payload/* id*/: string)

and on my effects I need the item instance so I do :

actions$.ofType(SELECT_ITEM)
  .map(toPayload)
  .withLatestFrom( this.store.select( getItems ) )
  .map( ([id, items]) => items[id] )

I think I could also do :

actions$.ofType(SELECT_ITEM)
  .withLatestFrom( () => this.store.select( getSelectedItem ) )

But it feels weird and It's still accessing the state.

[fxck]

Doing it in effects the reactive way is perfectly fine. The "problem" would be if you wanted to do something like..

http.post('/foo', state.value.people['3'].name); // accessing the "sync" state value

.. since there are better ways to handle this

[ghetolay]

What's wrong with accessing the state value ?

Because I've replaced

actions$.ofType(SELECT_ITEM)
  .map(toPayload)
  .withLatestFrom( this.store.select( getItems ) )
  .map( ([id, items]) => items[id] )

with

actions$.ofType(SELECT_ITEM)
  .map(toPayload)
  .map( id => this.getStateSnapshot( getItems )[id] )

in some of my effects and it seems to work good.
I can't see what could go wrong here.

[karolmie1]

@fxck What are those better ways? Can you show me where I should look for them?
Sometimes I want to have a snapshot, and sometimes I want a subscription.
It would be great if such native function existed.
If it's hard to do, simple alias for select(...).take(1) would be nice.

[AnianZ]

For me the only time I need a snapshot is in my logging service. If an error occurs I send a Request with the current state and the error message back to the server. It would be convenient to have something shorter as select(...).take(1) at this moment but it really doesn't hurt much. After all, that's only one case where I'd need it.

[sliekens]

I don't buy into the blanket statement that accessing the current state in a non-reactive manner is always bad. I know my code and at some points in my code I know that the store already contains the data that I need to retrieve. I also don't care if the data is subject to (frequent) changes. A snapshot is usually enough. That means I don't need to wait for data to become available and I should not need to subscribe to state changes just to get the latest available state.

Please provide some examples of why this is bad, or point me to a commit or issue where the removal of getState()/getValue()/value was discussed.

[robwormald]

Please check this against NgRx v4, and if it’s still an issue, please reopen on https://github.com/ngrx/platform. Thanks!