Combining input from shiny widgets and MySQL queries with less code - mysql

Question

I have an application that allows users to query MySQL database using input widgets on a shiny app. The queries involve joining tables too. The code becomes too long when employing IF ...ELSE statements to determine if a widget is empty or has some user input like in the code below.
Sample MySQL data can be created as below:
CREATE TABLE quoteauthors (
FirstName VARCHAR(255) ,
LastName VARCHAR(255) ,
authorID VARCHAR(255)
);
CREATE TABLE quotes (
quote VARCHAR(255) ,
authorID VARCHAR(255)
);
INSERT INTO quoteauthors
VALUES ('Albert', 'Einstein', 'a1'),
('Stephen', 'Hawking', 'a2'),
('Isaac', 'Newton', 'a3');
INSERT INTO quotes
VALUES ('Unthinking respect for authority is the greatest enemy of truth.', 'a1'),
('In the middle of difficulty lies opportunity.', 'a1'),
('Intelligence is the ability to adapt to change.', 'a2'),
('Science is not only a disciple of reason but, also, one of romance and passion.', 'a2'),
('If I have seen further it is by standing on the shoulders of Giants.', 'a3'),
('I can calculate the motion of heavenly bodies but not the madness of people', 'a3');
Sample shiny app is as below:
library(shiny)
library(shinydashboard)
library(DBI)
library(RMySQL)
ui <- dashboardPage(
dashboardHeader(),
dashboardSidebar(
sidebarMenu(
menuItem("QUOTE Search", tabName = "Tabs", icon = icon("object-ungroup"))
)
),
dashboardBody(
tabItem(tabName = "Tabs",
fluidRow(
column(width=3,
box(
title="Search ",
solidHeader=TRUE,
collapsible=TRUE,
width=NULL,
textInput("quoteSearch1", " Search Term 1 ", '', placeholder = "Type search term"),
radioButtons("combi", "Logical Operator to Combine Terms:",
c(
"AND" = "AND",
"OR" = "OR"
), inline = TRUE),
textInput("quoteSearch2", " Search Term 2 ", '', placeholder = "Type search term"),
selectInput("authorchoice", "Select AUTHOR", selected = NULL, multiple = T,
choices=c('Albert','Stephen','Isaac')),
submitButton("Search")
)
),
column( width=9,
tabBox(
width="100%",
tabPanel("Search Results",
htmlOutput("quotesearchdetails")
)))))))
server <- function(input, output) {
output$quotesearchdetails <-renderUI({
if(input$quoteSearch1!=""){
con <- dbConnect(MySQL(),
user='XXXXXXXXXXX',
port = 3306, password='XXXXXXXXXXX',
dbname='XXXXXXXXXXX',
host='XXXXXXXXXXX')
dbSendQuery(con, "SET NAMES utf8mb4;")
dbSendQuery(con, "SET CHARACTER SET utf8mb4;")
dbSendQuery(con, "SET character_set_connection=utf8mb4;")
on.exit(dbDisconnect(con), add = TRUE)
quotedetails <- reactive({
if (input$authorchoice == ""){
if (input$quoteSearch2 == ""){
dbGetQuery(con, statement =
paste0(" SELECT q.quote, a.FirstName, a.LastName
FROM quotes q
JOIN quoteauthors a
ON (q.authorID = a.authorID)
WHERE (q.quote LIKE '%",input$quoteSearch1,"%') "))
}else{
if (input$combi == "AND"){
dbGetQuery(con, statement =
paste0("
SELECT q.quote, a.FirstName, a.LastName
FROM quotes q
JOIN quoteauthors a
ON (q.authorID = a.authorID)
WHERE (q.quote LIKE '%",input$quoteSearch1,"%' AND
q.quote LIKE '%",input$quoteSearch2,"%')"))
}else{
dbGetQuery(con, statement =
paste0("
SELECT q.quote, a.FirstName, a.LastName
FROM quotes q
JOIN quoteauthors a
ON (q.authorID = a.authorID)
WHERE (q.quote LIKE '%",input$quoteSearch1,"%'
OR q.quote LIKE '%",input$quoteSearch2,"%')"))
}
}
}else{
if (input$quoteSearch2 == ""){
dbGetQuery(con, statement =
paste0("
SELECT q.quote, a.FirstName, a.LastName
FROM quotes q
JOIN quoteauthors a
ON (q.authorID = a.authorID)
WHERE (q.quote LIKE
'%",input$quoteSearch1,"%'
AND a.FirstName LIKE '%",input$authorchoice,"%') "))
}else {
if (input$combi == "AND"){
dbGetQuery(con, statement =
paste0("
SELECT q.quote, a.FirstName, a.LastName
FROM quotes q
JOIN quoteauthors a
ON (q.authorID = a.authorID)
WHERE (q.quote LIKE '%",input$quoteSearch1,"%' AND
q.quote LIKE '%",input$quoteSearch2,"%') AND
a.FirstName LIKE '%",input$authorchoice,"%' "))
}else{
dbGetQuery(con, statement =
paste0("
SELECT q.quote, a.FirstName, a.LastName
FROM quotes q
JOIN quoteauthors a
ON (q.authorID = a.authorID)
WHERE (q.quote LIKE '%",input$quoteSearch1,"%' OR
q.quote LIKE '%",input$quoteSearch2,"%')
AND
a.FirstName LIKE '%",input$authorchoice,"%' "))
}
}
}
})
outputed=""
quotedetailsreturned <- quotedetails()
if (dim(quotedetailsreturned)[1] > 0){
for(i in seq(from=1,to=dim(quotedetailsreturned)[1])){
outputed<-paste(outputed,
paste("Author's First name: ",quotedetailsreturned[i,"FirstName"]),
sep="<br/><br/>")
outputed<-paste(outputed,
paste("Author's Last name: ",quotedetailsreturned[i,"LastName"]),
sep="<br/><br/>")
outputed<-paste(outputed,
paste("Quote: ",quotedetailsreturned[i,"quote"]),
sep="<br/><br/>")
}
} else { outputed <-"your search yielded no results."}
HTML(outputed)
}else {
paste("Please input a search term at least in the first field")
}
})
}
shinyApp(ui, server)
I am seeking a solution on how to avoid the repetition and long codes using the IF...ELSE statements in my code. What best programming practices I could use to combine the MySQL queries with user input on various shiny widgets including textInput, radioButtons, selectize/selectInput and so on by considering some inputs can be left empty thus should not be considered in the query.

Answer 1

I would first build the query string only, step-by-step, adding each clause at a step according to the chosen settings. After it has been built, execute the query. Makes the code much shorter and easier to read.