Get data from mysql with json and plot with D3
Question
I am trying to plot mysql data with d3. I am using php to convert to json format. For testing purposes I followed the steps here and used my own php file on XAMPP. But when I open the the html file in my browser, it always displays a white page.
<?php
$mysqli = mysqli_connect("$host, $username, $password, $dbname");
$mysqli ->set_charset('utf8mb4');
$myArray = array();
if($result = $mysqli ->query("SELECT `date`, `volume` FROM `sensordata`"))
{
while ($row = $result->fetch_array(MYSQLI_ASSOC))
{
$myArray[] = $row;
}
header("Content-Type: application/json");
echo json_encode($myArray);
}
$result->close();
$mysqli ->close();
?>
It echoes in json format like so:
[{"date": "02-04-2021","volume": "606.51"},{"date": "03-04-2021","volume": "700.51"}]
I use the following code from the Site:
<!DOCTYPE html>
<meta charset="utf-8">
<html lang = "en">
<style> /* set the CSS */
.line {
fill: none;
stroke: steelblue;
stroke-width: 2px;
}
</style>
<body>
<script src="d3/d3.js"></script>
<script>
// set the dimensions and margins of the graph
var margin = {top: 20, right: 20, bottom: 30, left: 50},
width = 960 - margin.left - margin.right,
height = 500 - margin.top - margin.bottom;
// parse the date / time
var parseTime = d3.timeParse("%d-%m-%Y");
// set the ranges
var x = d3.scaleTime().range([0, width]);
var y = d3.scaleLinear().range([height, 0]);
// define the line
var valueline = d3.line()
.x(function(d) { return x(d.date); })
.y(function(d) { return y(d.volume); });
// append the svg obgect to the body of the page
// appends a 'group' element to 'svg'
// moves the 'group' element to the top left margin
var svg = d3.select("body").append("svg")
.attr("width", width + margin.left + margin.right)
.attr("height", height + margin.top + margin.bottom)
.append("g")
.attr("transform","translate(" + margin.left + "," + margin.top + ")");
// Get the data
d3.json("get_data.json", function(error, data) {
if (error) throw error;
// format the data
data.forEach(function(d) {
d.date = parseTime(d.date);
d.volume = +d.volume;
});
// Scale the range of the data
x.domain(d3.extent(data, function(d) { return d.date; }));
y.domain([0, d3.max(data, function(d) { return d.volume; })]);
// Add the valueline path.
svg.append("path")
.data([data])
.attr("class", "line")
.attr("d", valueline);
// Add the X Axis
svg.append("g")
.attr("transform", "translate(0," + height + ")")
.call(d3.axisBottom(x)
.tickFormat(d3.timeFormat("%d-%m-%Y")));
// Add the Y Axis
svg.append("g")
.call(d3.axisLeft(y));
});
</script>
</body>
If I use variables like these:
var data = [
{date:"30-05-12",volume:"123"},
{date:"27-05-12",volume:"67.00"},
{date:"26-06-12",volume:"89.70"},
{date:"25-07-12",volume:"99.00"}
];
instead of this part:
// Get the data
d3.json("get_data.json", function(error, data) {
if (error) throw error;
// format the data
data.forEach(function(d) {
d.date = parseTime(d.date);
d.volume = +d.volume;
});
everything is fine and the data gets plotted.
All files are in the same folder.
Could someone please help me?
2 answers
solution1
0 2021-04-04 00:16:47
You are requesting a JSON file here, not your PHP file:
d3.json("get_data.json", ...)
So you might want to either request your PHP file, or write the JSON data to a *.json file in advance:
if($result = $mysqli ->query("SELECT `date`, `volume` FROM `sensordata`"))
{
...
file_put_contents('get_data.json', json_encode($myArray));
}
Also, your date format differs between the PHP output you've given and the hardcoded one ('02-04-2021' vs. '30-05-12'). If you like to stick with the latter, you might want to adapt your code's date format string (given it's used by d3.js to also parse a date):
var parseTime = d3.timeParse("%d-%m-%y")
For d3.json(), see also their docs .
solution2
0 2021-04-04 08:36:39
I think i got it in D3 5.0 they changed the syntax of d3.json , with the new syntax my code looks like this:
d3.json("get_data.php").then(function(data) {
// format the data
data.forEach(function(d) {
d.date = parseTime(d.date);
d.volume = +d.volume;
});
Old code:
d3.json("get_data.json", function(error, data) {
if (error) throw error;
// format the data
data.forEach(function(d) {
d.date = parseTime(d.date);
d.volume = +d.volume;
});
Now the data gets plotted.
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