Storing reactive data in shiny from SQL - r

Question

This is a follow up from this question:
Acessing SQL database using shiny with reactive query
I am trying to build a data frame from data fetched from an SQL database using a shiny app. Currently i am able to query the database and return one set of data. Now I would like to save that data to a data frame and then add more data from subsequent queries. Here is my code:
UI
library(markdown)
shinyUI(fluidPage(
titlePanel("Generic grapher"),
sidebarLayout(
sidebarPanel(
numericInput("wafer", label = h3("Select wafer ID:"), value = NULL),
actionButton("do", "An action button")
),
mainPanel(
verbatimTextOutput("value"), verbatimTextOutput("que"), dataTableOutput(outputId="pos")
)
)
)
)
Server:
library(RMySQL)
library(DBI)
library(sqldf)
con = dbConnect(RMySQL::MySQL(), dbname="xx", username="pete", password="xx", host="xx", port=3306)
query <- function(...) dbGetQuery(con, ...)
wq = data.frame()
shinyServer(function(input, output){
d <- eventReactive(input$do, { input$wafer })
output$value <- renderPrint({ d() })
a <- reactive({ paste("Select id from wafer where wafer_id=",d(), sep="") })
output$que <- renderPrint({ a() })
wq <- reactive({ query( a() ) })
output$pos <- renderDataTable({ wq() })
})
Now I am trying to use the information from these two answers to store the data from each search I do in a data frame:
Add values to a reactive table in shiny
What's the difference between Reactive Value and Reactive Expression?
New Server:
library(RMySQL)
library(DBI)
library(sqldf)
con = dbConnect(RMySQL::MySQL(), dbname="xx", username="pete", password="xx", host="xx", port=3306)
query <- function(...) dbGetQuery(con, ...)
wq = data.frame()
shinyServer(function(input, output){
values <- reactiveValues()
values$df <- data.frame()
d <- eventReactive(input$do, { input$wafer })
output$value <- renderPrint({ d() })
a <- reactive({ paste("Select id from wafer where wafer_id=",d(), sep="") })
output$que <- renderPrint({ a() })
wq <- reactive({ query( a() ) })
values$df <- reactive({ rbind(values$df, wq() ) })
output$pos <- renderDataTable({ values$df })
})
However, when I do this the data table never renders within my app. I dont have an error message. Any ideas where Im going wrong? Any help appreciated!

Answer 1

I think changing
values$df <- reactive({ rbind(values$df, wq() ) })
in your new server.R to
observe({
values$df <- rbind(isolate(values$df), wq())
})
might fix your problem.
EDIT: Here's a working example using a local connection:
library(markdown)
library(RMySQL)
library(DBI)
library(sqldf)
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "mtcars", mtcars)
query <- function(...) dbGetQuery(con, ...)
wq = data.frame()
ui <- shinyUI(fluidPage(
titlePanel("Generic grapher"),
sidebarLayout(
sidebarPanel(
numericInput("wafer", label = h3("Select number of cylinders:"),
value = NULL),
actionButton("do", "An action button")
),
mainPanel(
verbatimTextOutput("value"),
verbatimTextOutput("que"),
verbatimTextOutput("wq_print"),
dataTableOutput(outputId="pos")
)
)
)
)
server <- shinyServer(function(input, output){
values <- reactiveValues()
values$df <- data.frame()
d <- eventReactive(input$do, { input$wafer })
output$value <- renderPrint({ d() })
a <- reactive({ paste("SELECT * FROM mtcars WHERE cyl = ", d(), sep="") })
output$que <- renderPrint({ a() })
observe({
if (!is.null(d())) {
wq <- reactive({ query( a() ) })
output$wq_print <- renderPrint({ print(str(wq())) })
values$df <- rbind(isolate(values$df), wq())
}
})
output$pos <- renderDataTable({ values$df })
})
shinyApp(ui, server)
The relevant changes to your original code are the !is.null(d()) condition for handling the initial NULL value of d(), and using values$df <- rbind(isolate(values$df), wq()) inside an observer. Hope this helps with fixing your code!