R Shiny: Build an interactive SQL query and copy data into global environment - sql

Question

I try to build a shiny app that enables users to query data. Users are supposed to provide a list of values of interest that are used to filter data stored in a database. Unfortunately, dplyr's translation does not appear to be the most efficient/performant solution such that I have to build a string and pass it to the database via sql(). The string manipulations are also a crude fail safe to handle entry errors/varieties. The following code illustrates this string building and data query process:
library(tibble)
library(dplyr)
library(dbplyr)
library(shiny)
library(RSQLite)
library(DBI)
library(stringr)
# Create string variables to experiment
mtcars1 <- tibble::rownames_to_column(mtcars, var = "model") %>% # Create column based on row names
dplyr::mutate(carmaker = stringr::word(model, 1)) # Create column with first word of column with row names
# Establish example database
con <- DBI::dbConnect(RSQLite::SQLite(), path = ":memory:")
copy_to(con, mtcars1, "mtcars1", temporary = FALSE)
# Query example
# Input
string_input <- "Mazda, Merc"
# Prepare input string to be used in SQL
string_filter <- string_input %>%
base::gsub("[,]+", " ", .) %>% # remove commas
stringr::str_squish(.) %>% # remove multiple blanks
base::gsub(" ", ",", .) %>% # substitute blanks for commas
base::gsub("(\\w+)", "'\\1'", .) %>% # enclose words with single quotation marks
base::paste0("carmaker in (", ., ")") # create sql where statement
# Data query
data <- tbl(con, "mtcars1") %>%
filter(sql(string_filter)) %>%
show_query() %>%
collect()
I'd like to implement this code in a shiny app:
# Shiny user interface
ui <- fluidPage(
textInput(inputId = "string_input", label = "Input", value = "", placeholder = "Enter list of car models without commas"),
actionButton(inputId = "go", label = "Go"),
textOutput(outputId = "string_output")
)
# Shiny server function
server <- function(input, output){
observeEvent(input$go, {
output$string_output <- reactive({input$string_input %>%
base::gsub("[,]+", " ", .) %>% # remove commas
stringr::str_squish(.) %>% # remove multiple blanks
base::gsub(" ", ",", .) %>% # substitute blanks for commas
base::gsub("(\\w+)", "'\\1'", .) %>% # enclose words with single quotation marks
base::paste0("carmaker in (", ., ")") # create sql where statement
})
})
}
# Launch shiny app
shinyApp(ui, server)
The app takes to list of values supplied by the user as input, transforms it and shows the transformed list as output.
Here is what I want to do:
I would like store the transformed string_input in an extra local object for further use in the app, that is, I want to pass the string_input to the data query similar to the non-shiny example above.
I would like to copy the data query result to R's global environment such that I can use it, even after closing the app.
Regarding the my second point: I read that one can use <- and <<-, but I could not make it work in a reactive context.

Answer 1

I figured out the solution:
library(tibble)
library(dplyr)
library(dbplyr)
library(shiny)
library(RSQLite)
library(DBI)
library(stringr)
# Create string variables to experiment
mtcars1 <- tibble::rownames_to_column(mtcars, var = "model") %>% # Create column based on row names
dplyr::mutate(carmaker = stringr::word(model, 1)) # Create column with first word of column with row names
# Establish example database
con <- DBI::dbConnect(RSQLite::SQLite(), path = ":memory:")
copy_to(con, mtcars1, "mtcars1", temporary = FALSE)
# Shiny user interface
ui <- fluidPage(
textInput(inputId = "string_input",
label = "Input",
value = "",
placeholder = "Enter a list of car makers (e.g. Mazda, Merc)"),
textOutput(outputId = "string_output"),
actionButton(inputId = "go", label = "Go"),
tableOutput(outputId = "data_output")
)
# Custom function to save reactive object to global environment
saveData <- function(x) {
export <<- x
}
# Shiny server function
server <- function(input, output){
list <- reactive({
input$string_input %>%
base::gsub("[,]+", " ", .) %>% # remove commas
stringr::str_squish(.) %>% # remove multiple blanks
base::gsub(" ", ",", .) %>% # substitute blanks for commas
base::gsub("(\\w+)", "'\\1'", .) %>% # enclose words with single quotation marks
base::paste0("carmaker in (", ., ")") # create sql where statement
})
output$string_output <- reactive({list()})
data <- eventReactive(input$go, {
tbl(con, "mtcars1") %>%
dplyr::filter(sql(!!list())) %>%
dplyr::collect()
})
output$data_output <- renderTable(data())
observeEvent(input$go, {
saveData(data())
})
}
# Launch shiny app
shinyApp(ui, server)
The trick was to define the function saveData, pass the reactive data object to it and assign it to export via <<-.
Honestly, I do not understand all of the fundamentals so any suggestions for improvement are welcome. However, it works.

Answer 2

For your first question:
# Shiny server function
server <- function(input, output){
string_output <- eventReactive(input$go, {
input$string_input %>%
base::gsub("[,]+", " ", .) %>% # remove commas
stringr::str_squish(.) %>% # remove multiple blanks
base::gsub(" ", ",", .) %>% # substitute blanks for commas
base::gsub("(\\w+)", "'\\1'", .) %>% # enclose words with single quotation marks
base::paste0("carmaker in (", ., ")") # create sql where statement
})
output$string_output <-renderText(string_output())
}
string_output() reactive function is now available for output as well as for data query.
Note that you could also use input$string_input instead of input$goas trigger to update the output while you type the criteria.
You can then use input$go to query the data:
data <- eventReactive(input$go, { dbGetQuery(yourConnection,YourQuery(string_output())})
output$data <- renderTable(data())
Not sure you can directly write from Shiny to R's environment, but you can for sure save data() as a file on the server.