Get value from reactive context in R shiny based on user input - r

Question

I need to change the mydb(string) value based on input selected from sidebar.
ui.R
library(shiny)
shinyUI(fluidPage(
titlePanel("Shiny App"),
sidebarLayout(
sidebarPanel( selectInput("site",
label = "Choose a site for Analysis",
choices = c("abc", "def",
"ghi", "jkl"),
selected = "abc")
),
mainPanel(
textOutput("text"),
)
))
server.R
library(shiny)
library(ggplot2)
library(RMySQL)
shinyServer(function(input, output) {
if(input$site=="abc"){
mydb<-"testdb_abc"}
else if(input$site=="def"){
mydb<-"testdb_def"}
con <- dbConnect(MySQL(),dbname=mydb, user="root", host="127.0.0.1", password="root")
query <- function(...) dbGetQuery(con, ...)
output$text <- renderText({
paste("You have selected:",input$site)
})
})
In above server.R, I need to assign string value to mydb based on selected input. I get this error:
Error in .getReactiveEnvironment()$currentContext() :
Operation not allowed without an active reactive context. (You tried to do something that can only be done from inside a reactive expression or observer.)
How can I do that with reactive in shiny?

Answer 1

as previously mentioned you would have to have your if statements in the reactive expression or observe Below is the working example of the sample App. Here I used a reactive expression to check which database you have selected. you can then use the mydb() and put it into your query, like so (I think this should work):
con <- dbConnect(MySQL(),dbname=mydb(), user="root", host="127.0.0.1", password="root")
query <- function(...) dbGetQuery(con, ...)
A sample example is below
library(shiny)
library(ggplot2)
library(RMySQL)
ui =fluidPage(
titlePanel("Shiny App"),
sidebarPanel(selectInput("site",
label = "Choose a site for Analysis",
choices = c("abc", "def","ghi", "jkl"),selected = "abc")),
mainPanel(textOutput("text"),textOutput("db_select"))
)
server = (function(input, output) {
mydb <- reactive({
if(input$site == "abc")
{
test <- c("testdb_abc")
}
else if(input$site == "def")
{
test <- c("testdb_def")
}
})
output$text <- renderText({
paste("You have selected:",input$site)
})
query_output <- reactive({
con <- (dbConnect(MySQL(),dbname=mydb(), user="root", host="127.0.0.1", password="root"))
query <- function(...) dbGetQuery(con, ...)
})
output$db_select <- renderText({
paste("My Database is:",mydb())
})
})
runApp(list(ui = ui, server = server))