Как добавить слой в openlayer3, используя ajax?

Я новичок в Openlayers3 ….. Я пытаюсь загрузить данные из базы данных, используя ajax & PHP, чтобы загрузить векторные данные в openlayers3, я застрял и не знаю, в чем проблема.
вот мой код
Кто-нибудь может мне помочь в этом?

$(document).ready(function()
{
//extent of the map
view = new ol.View({
center:ol.proj.transform([125.7799,8.7965], 'EPSG:4326', 'EPSG:3857'),
zoom:11,
maxZoom:18,
minZoom:2
});

//BaseLayer
var baseLayer = new ol.layer.Tile({
source: new ol.source.OSM()
});

// create a vector source that loads a GeoJSON file
var vectorSource = new ol.source.Vector({
projection: 'EPSG:4326',
url: 'data/Boundaries.geojson',
format: new ol.format.GeoJSON()

});

var geoJSONFormat = new ol.format.GeoJSON();

var farmersSource = new ol.source.Vector({
loader: function(extent, resolution, projection) {
var url = 'allfarmers_geojson.php?p=' + extent.join(',');
$.ajax({
url: url,
success: function(data) {
var features = geoJSONFormat.readFeatures(data);
farmersSource.addFeatures(features);
}
});
},
strategy: ol.loadingstrategy.bbox
});// Polygons
var createPolygonStyleFunction = function() {
return function(feature, resolution) {
var style = new ol.style.Style({
stroke: new ol.style.Stroke({
color: 'blue',
width: 1

}),
fill: new ol.style.Fill({
color: '#faeaac'
}),
//text: createTextStyle(feature)
});
return [style];
};
};

// a vector layer to render the source
var vectorLayer = new ol.layer.Vector({
source: vectorSource,
style:createPolygonStyleFunction()

});

var farmersLayer = new ol.layer.Vector({
source: farmersSource
//style:createPolygonStyleFunction()

});

//Map
var map = new ol.Map({
target:'map',
controls:ol.control.defaults().extend([
new ol.control.ScaleLine(),
new ol.control.ZoomSlider()
]),
renderer: 'canvas',
layers:[baseLayer,vectorLayer,farmersLayer],
view:view
});

//////////styling features and with mouse over color change/////////////
var highlightStyleCache = {};

var featureOverlay = new ol.layer.Vector({
source: new ol.source.Vector(),
map: map,
style: function(feature, resolution) {
var text = resolution < 5000 ? feature.get('NAME_3') : '';
if (!highlightStyleCache[text]) {
highlightStyleCache[text] = new ol.style.Style({
stroke: new ol.style.Stroke({
color: '#f00',
width: 1
}),
fill: new ol.style.Fill({
color: 'rgba(255,0,0,0.1)'
}),
text: new ol.style.Text({
font: '12px Calibri,sans-serif',
text: text,
fill: new ol.style.Fill({
color: '#f00'
})
})
});
}
return highlightStyleCache[text];
}
});

var highlight;
var displayFeatureInfo = function(pixel) {

var feature = map.forEachFeatureAtPixel(pixel, function(feature) {
return feature;
});

if (feature !== highlight) {
if (highlight) {
featureOverlay.getSource().removeFeature(highlight);
}
if (feature) {
featureOverlay.getSource().addFeature(feature);
}
highlight = feature;
}

};

map.on('pointermove', function(evt) {
if (evt.dragging) {
return;
}
var pixel = map.getEventPixel(evt.originalEvent);
displayFeatureInfo(pixel);
});

map.on('click', function(evt) {
displayFeatureInfo(evt.pixel);
});
//////////End of styling features and with mouse over color change/////////////

});

и вот мой файл php

<?php
$conn = new PDO('mysql:host=localhost;dbname=FarmersDB','root','admin');

$sql = 'SELECT *, _coordinates__latitude AS x, _coordinates__longitude AS y FROM farmers';

if (isset($_GET['bbox']) || isset($_POST['bbox'])) {
$bbox = explode(',', $_GET['bbox']);
$sql = $sql . ' WHERE x <= ' . $bbox[2] . ' AND x >= ' . $bbox[0] . ' AND y   <= ' . $bbox[3] . ' AND y >= ' . $bbox[1];
}

$rs = $conn->query($sql);
if (!$rs) {
echo 'An SQL error occured.\n';
exit;
}

$geojson = array(
'type'      => 'FeatureCollection',
'features'  => array()
);while ($row = $rs->fetch(PDO::FETCH_ASSOC)) {
$properties = $row;

unset($properties['x']);
unset($properties['y']);
$feature = array(
'type' => 'Feature',
'geometry' => array(
'type' => 'Point',
'coordinates' => array(
$row['x'],
$row['y']
)
),
'properties' => $properties
);

array_push($geojson['features'], $feature);
}

header('Content-type: application/json');
echo json_encode($geojson, JSON_NUMERIC_CHECK);
$conn = NULL;
?>