How to use R Shiny reactive server objects in UI input widgets - r

Question

I'm trying to have a Shiny app, that is connecting to a database, but the IP and so an can be modified by a User.
In short, I kind of just want to know, if its possible to have a shiny app, with objects from reactiv server parts included in the UI select inputs.
Like this:
library(shiny)
ui <- fluidPage(
selectizeInput(inputId = 'inSelect',
label = "countries",
choices = getTable(),
multiple = TRUE,
options = list(maxItems = 4,
placeholder = 'select up to 4 countries')
)
)
server <- function(input, output) {
getTable <- reactive({
country <- data.frame(name=c("Germany","France","Japan"),
code=c("DEU","FRA","JPN"))
countryN <- country$code
names(countryN) <- country$name
})
}
shinyApp(ui = ui, server = server)
when it works, it should look like this:
I know, that I can achieve this effect, by just building the DF before the UI, but my real problem is ab bit more complicated:
I want the user to type in IP, Username,PW, and DB name, to connect to the DB.
After a button click, the connection should be established and the df. country should be pulled out of the DB, not constructed.
I think, that I have to do this part in the (reactive) Server part, because I am using Input$x in the DB connection.
I hope, that my vision is somehow possible and you guys can help me,
Thanks.

Answer 1

you can use updateSelectInput() to update a select input from the server side of the app more info found here: https://shiny.rstudio.com/reference/shiny/1.2.0/updateSelectInput.html
in your specific example you can achieve this by:
library(shiny)
ui <- fluidPage(
selectizeInput(inputId = 'inSelect',
label = "countries",
choices = NA,
multiple = TRUE,
options = list(maxItems = 4,
placeholder = 'select up to 4 countries')
)
)
server <- function(input, output,session) {
getTable <- reactive({
country <- data.frame(name=c("Germany","France","Japan"),
code=c("DEU","FRA","JPN"))
countryN <- country$code
names(countryN) <- country$name
return(country)
})
observe({updateSelectInput(session, inputId="inSelect", label = NULL, choices = getTable()$name,
selected = NULL)})
}
shinyApp(ui = ui, server = server)
by adding the argument session to the server function and then using the updateSelectInput() function, this must be wrapped in a reactive expression in this example I used observe()