How to periodically fetch data from psql table
Question
I am fetching data from a psql table and passing it to javascript as json array for display as a time series chart. The data passed needs to be in the from of an array.
As the data in the table is updated periodically, I need to constantly fetch the data from psql eg every 15 minutes and pass updated array to javascript.
I search but so far I couldn't any solution. My question is how can I fetch data from psql periodically.
Here is my code:
<!DOCTYPE html>
<html lang="en">
<head>
<script>
var Device_Data;
var time, batt;
var timeArray = [];
var battArray = [];
var N = 12;
for (i = 0; i < N; i++) {
timeArray.push(0);
battArray.push(0); }
function dspChrt(Device_Data) {
console.log(Device_Data[0].date_time);
console.log(Device_Data[1].battery_voltage_mv);
time = Device_Data[0].date_time;
batt = Device_Data[1].battery_voltage_mv;
timeArray.shift();
timeArray.push(time);
battArray.shift();
battArray.push(batt);
</script>
</head>
<body>
<?php
require("Connection.php");
$stmt = $conn->prepare("Select date_time, battery_voltage_mv FROM measuring_device_statuses order by date_time desc limit 12");
$stmt->execute();
$result = $stmt->setFetchMode(PDO::FETCH_ASSOC);
$WData = $stmt->fetchAll();
/*
echo "<pre>".print_r($WData, true)."</pre>";
die();
*/
?>
<script>
var WData = <?php print_r(json_encode($WData));?>;
//console.log(WData);
dspChrt(WData);
</script>
</body>
</html>
2 answers
solution1
0 2018-11-08 13:25:44
将您的数据提取php脚本保存在某个文件“ fetch.php”中，并通过javascript设置间隔函数定期调用它，例如，此代码每3秒打印一次警报。
setInterval(function(){ alert("Hello"); }, 3000);
solution2
0 2018-11-08 13:28:07
You can use AJAX for this purpose.
HTML
<div id="myDiv"></div>
JavaScript
<script>
window.onload = function(){
loadDoc();
SetInverval(loadDoc, (10000 * 60 * 15)); // Perform function every fifteen minutes
}
function loadDoc() {
var div = document.getElementById("myDiv"); // Get Div
div.innerHTML = ""; // Set to nothing
var xhttp = new XMLHttpRequest(); // Create new XML object
xhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) { // If successful
div.innerHTML = this.responseText; // Display result
}
};
xhttp.open("GET", "loadDoc.php", true);
xhttp.send();
}
This should be in your PHP file, named loadDoc.php or whatever you choose to replace it to.
<?php
require("Connection.php");
$stmt = $conn->prepare("SELECT date_time, battery_voltage_mv FROM measuring_device_statuses ORDER BY date_time DESC LIMIT 12");
$stmt->execute();
//$result = $stmt->setFetchMode(PDO::FETCH_ASSOC);
$WData = $stmt->fetchAll();
$stmt->close();
echo "<pre>".print_r($WData, true)."</pre>";
die();
?>
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