Call PHP function with JavaScript Ajax to get database values - php

Question

i try to call a php function with Ajax. This is my JavaScript code in my html file:
<script type="text/javascript">
function ajax(){
$.ajax({
type:"POST",
url: "SQLCommunication.php",
dataType: "JSON",
success : function(json){
json = jQuery.parseJSON(json);
alert(json.value);
}
}
)
}
$("#btn_refresh").click(function(){
ajax();
});
</script>
I don't know if i have to specify which PHP function i actually want to call? I also don't know how i do that.
My PHP function:
header('Content-Type: application/json');
function readValue(){
$conn = establishConnection();
if($conn->connect_error){
die("Connection failed: " . $conn->connect_error);
}
$sql = "SELECT datetime, value FROM tempvalues";
$result = $conn->query($sql);
if($result->num_rows > 0){
$row = $result->fetch_assoc();
$arr["datetime"] = $row["datetime"]; //return datetime and value as array
$arr["value"] = $row["value"];
if(is_ajax()){
return json_encode($arr);
} else {
return $arr;
}
}
$conn->close();
}
So the problem is now, that nothing happens if i press the button.

Answer 1

I'll rewrite to my style
jQuery
<script type="text/javascript">
$("#btn_refresh").click(function(){
$.ajax({
type:"POST",
url: "SQLCommunication.php",
dataType: "JSON",
success : function(data){
console.log(data);
if(data.status === "success"){
alert("success");
}else{
alert("error");
}
}
error : function(XHR, status){
alert("fatal error");
}
})
});
</script>
PHP
header('Content-Type: application/json');
function readValue(){
$conn = establishConnection();
if($conn->connect_error){
die("Connection failed: " . $conn->connect_error);
}
$sql = "SELECT datetime, value FROM tempvalues";
$result = $conn->query($sql);
if($result->num_rows > 0){
$row = $result->fetch_assoc();
$arr["datetime"] = $row["datetime"]; //return datetime and value as array
$arr["value"] = $row["value"];
$arr["status"] = "success";
}else{
$arr["status"] = "error";
}
return json_encode($arr);
$conn->close();
}
echo readValue();
Untested
Updated
functions.php
function readValue(){
$conn = establishConnection();
if($conn->connect_error){
die("Connection failed: " . $conn->connect_error);
}
$sql = "SELECT datetime, value FROM tempvalues";
$result = $conn->query($sql);
if($result->num_rows > 0){
$row = $result->fetch_assoc();
$arr["datetime"] = $row["datetime"]; //return datetime and value as array
$arr["value"] = $row["value"];
$arr["status"] = "success";
}else{
$arr["status"] = "error";
}
return json_encode($arr);
$conn->close();
}
function writeValue(){
...
}
SQLCommunication.php
header('Content-Type: application/json');
if(!isset($_GET['func']) && empty($_GET['func'])){
//make the file inaccessible without $_GET
$arr['status'] = "error";
echo json_encode($arr);
exit();
)
if($_GET['func'] === "readvalue"){
echo readValue();
}elseif($_GET['func'] === "writevalue"){
echo writeValue();
}elseif($_GET['func'] === "whatever"){
//whatever...
}
....
jQuery
$("#btn_refresh").click(function(){
$.ajax({
type:"POST",
url: "SQLCommunication.php?func=readvalue", //SQLCommunication.php?func=writevalue
dataType: "JSON",
success : function(data){
console.log(data);
if(data.status === "success"){
alert("success");
}else{
alert("error");
}
}
error : function(XHR, status){
alert("fatal error");
}
})
});

Answer 2

If you want to see the result in your ajax response, you have to use echo(), or any other printing method in your controller instead of return