Use Shiny App to Query a SQL Server DB - r

Question

I guess I really don't understand this process like I thought I did. I found the link below, and it seems pretty helpful, but after making only slight modifications, I can't get it to do what I want.
R Shiny SQL Server Query
I just want to launch a webpage and have a user enter a parameter, to be passed into a query.
library(RODBCext)
library(shiny)
ui <- shinyUI(
pageWithSidebar(
headerPanel("Hide Side Bar example"),
sidebarPanel(
textInput("CATEGORY", "Enter CATEGORY below"),
submitButton(text="Submit")
),
mainPanel(
tabsetPanel(
tabPanel("Data", tableOutput("tbTable"))
)
)
)
)
browser()
server <- function(input, output, session)
myData <- reactive({
req(input$Id)
#connect to database
dbhandle = odbcDriverConnect('driver={SQL Server};server=my_server;database=data_WH;trusted_connection=true')
browser()
#build query
#query = "SELECT * FROM [my_db].[dbo].[my_table] where [CATEGORY] = '1070'"
query = "SELECT * FROM [my_db].[dbo].[my_table] where [CATEGORY] = ?"
browser()
#store results
res <- sqlExecute(channel = dbhandle,
query = query,
data = list(input$Id),
fetch = TRUE,
stringsAsFactors = FALSE)
#close the connection
odbcClose(dbhandle)
#return results
res
})
output$tbTable <-
renderTable(
myData()
)
shinyApp(ui = ui, server = server)
The SQL string is fine. I entered browser, to try to debug the script, as described in the link below.
https://shiny.rstudio.com/articles/debugging.html
browser()
It didn't pause the code; it didn't help me debug the code. It didn't do anything at all.
Any thoughts anyone?

Answer 1

It looks like your server function is incorrectly defined.
A function defined of the form
fn <- function(arg1, arg2)
expression1
expression2
Is actually going to be evaluated as
fn <- function(arg1, arg2){
expression1
}
expression2
In your server function, because you didn't place your braces, the only expression in the function definition is creating the myData reactive. Your output$tbTable element is completely separate from your function, never gets called in the app, and so your reactive is never processed. You should try this:
library(RODBCext)
library(shiny)
ui <- shinyUI(
pageWithSidebar(
headerPanel("Hide Side Bar example"),
sidebarPanel(
textInput("CATEGORY", "Enter CATEGORY below"),
submitButton(text="Submit")
),
mainPanel(
tabsetPanel(
tabPanel("Data", tableOutput("tbTable"))
)
)
)
)
server <- function(input, output, session)
{ # NOTE THE BRACE HERE
myData <- reactive({
req(input$CATEGORY)
#connect to database
dbhandle = odbcDriverConnect('driver={SQL Server};server=my_server;database=data_WH;trusted_connection=true')
#build query
#query = "SELECT * FROM [my_db].[dbo].[my_table] where [CATEGORY] = '1070'"
query = "SELECT * FROM [my_db].[dbo].[my_table] where [CATEGORY] = ?"
#store results
res <- sqlExecute(channel = dbhandle,
query = query,
data = list(input$CATEGORY),
fetch = TRUE,
stringsAsFactors = FALSE)
#close the connection
odbcClose(dbhandle)
#return results
res
})
output$tbTable <-
renderTable(
myData()
)
} # AND NOTE THE CLOSING BRACE HERE
shinyApp(ui = ui, server = server)