Any simple clean way to attach info to a session?

[daattali]

x-post from shiny-discuss

Suppose I have a package with an exported function that can be called from other people's shiny apps' server code. I want to know whether it's the first time they call this function or not. What's the best way to do this?

I can add an attribute to the session object but that sounds like a bad idea. I feel like there should be a simple solution I'm not seeing

Example pseudocode:

# This function would be in a package
myfunc <- function() {
  if (firsttime) {
    ...
  } else {
    ..
  }
}

And any shiny app can call it in server code, potentially multiple times

ui <- fluidPage()
server <- function(input, output, session) {
  mypkg::myfunc()
}

If I was working on a regular R package without a shiny app, I would use a global environment to store this global value. But in this case I want this to be per-session.

This isn't an issue, it's a question that's gotten no response on shiny-discuss. I might be abusing the Issues system, but I thought this would be a bit more considerate than my usual method of personally emailing @jcheng5

[jcheng5]

Sorry, I've been busier than usual the last few weeks. This is an important capability (we've needed it ourselves a couple of times recently) and so easy to add.

I'm envisioning session$userData$foo <- 10. Only question I have is whether session$userData should be a regular environment, or a reactiveValues? (If the former, if you needed reactivity you could create a reactiveValues object and put it into a slot in the regular environment; but if the common case is needing reactivity it might be nicer to do the latter.)

[daattali]

For my specific case a regular environment is good enough, but I would think making it reactiveValues would be useful. I'd vote for the latter.

This wouldn't be backwards compatible though - for older shiny versions, would attaching an attribute to session be the least terrible way of achieving this?

[jcheng5]

@daattali Huh, does attaching an attribute work? If so, that's a fine hack. 👍

[daattali]

Yup, you can't session$foo <- "bar" because of locked environments, but R is perfectly happy with attr(session, "foo") <- "bar".

Wanted to see if you had any reason to discourage me from doing that. I got your thumbs up though so I'm happy

[bborgesr]

I like the idea of having this explicitly as a session element. It seems handy. However, I think I'm missing why exactly this isn't possible as of now without tacking an attribute onto the session object.

The scoping rules for shiny:

# shared across all sessions
a <- "all"

ui <- fluidPage()

server <- function(input, output, session) {
  # defined in each session
  s <- "session"

  output$text <- renderText({
    # defined each time this function is called
    f <- "function"
  })
}

Why isn't s what you need?

In your case:

ui <- fluidPage()
server <- function(input, output, session) {
  wasCalled <- 0
  
 observe({  # or a render func or a reactive
    # the logic / conditionals you need...
    mypkg::myfunc()
    wasCalled <<- wasCalled + 1
  })
}

[daattali]

That works fine when you're developing the entire shiny app yourself. But what if I want to do this from a separate package that is called from the end user's shiny app? I won't have access to the server function.

…

On Dec 15, 2016 8:22 AM, "Barbara Borges Ribeiro" ***@***.***> wrote: I like the idea of having this explicitly as a session element. It seems handy. However, I think I'm missing why exactly this isn't possible as of now without tacking an attribute onto the session object. The scoping rules for shiny: # shared across all sessionsa <- "all" ui <- fluidPage() server <- function(input, output, session) { # defined in each session s <- "session" output$text <- renderText({ # defined each time this function is called f <- "function" }) } Why isn't s what you need? In your case: ui <- fluidPage()server <- function(input, output, session) { wasCalled <- 0 observe({ # or a render func or a reactive # the logic / conditionals you need... mypkg::myfunc() wasCalled <<- wasCalled + 1 }) } — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#1512 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AA6IFFXldq3e2syFPIfqU9U1cp1c1qX5ks5rIT8TgaJpZM4LNtTF> .

[jcheng5]

Yep, this is for advanced usage by module and package authors.

[bborgesr]

Got it, thanks!

[davidlub]

Hi,

The shinyStore package for storing local data using the HTML 5 storage is easy to use and works well. You could use it to store info per browser (not per session).

David