R-Shiny using Reactive renderUI value

Question

How do you use values obtained from a renderUI element in a reactive wrapper?

i.e. My code:

CompanyNames <- sqlQuery(connection, "SELECT Companynm FROM RiskMgm_Company")

output$CompNameSelector <- renderUI({ 
selectInput("compName","Company Name:",as.vector(CompanyNames[,1]))
})

 CompID <- reactive({
CompID <<- sqlQuery(paste("SELECT CompanyID FROM RiskMgm_Company WHERE Companynm = '",compName,"'"))
})

output$MotorSelector <- renderUI({
selectInput("MachSer","Machine:",sqlQuery(connection,paste("SELECT Motor_func FROM RiskMgm_Motor WHERE Company_ID='",CompID,"'")))
})

My error:

Successfilly opened connection to db
Error in paste("SELECT CompanyID FROM RiskMgm_Company WHERE Companynm = '",  : 
could not find function "compName"

What am I doing wrong? Essentially what I want is a list of companies given by the SQL query. Then depending on the Company selected it will show the motors that belong to that company in the next dropdown box

Thanks

Answer 1

You would refer to the elements by their id for example input$compName. As a contrived example here is a simple shiny app with two selectInput's. The second selectInput choices depend on the value of the first. Referencing the output of widgets created by renderUI is no different from referencing the same widgets if they had been in UI.R from the beginning:

library(shiny)
myDF <- data.frame(A = 1:4, B = 3:6, C = 6:9, D = 10:13)
runApp(
  list(
    ui = fluidPage(
      uiOutput("myList"),
      uiOutput("myNumbers")
      )
    , server = function(input, output, session){
      output$myList <- renderUI({
        selectInput("compName", "Company Name:", LETTERS[1:4])
      })

      output$myNumbers <- renderUI({
        selectInput("compNo", "Product Line:", myDF[, input$compName])
      })
    }
    )
  )