Here is a more complete code regarding wfs-t:
var format = new ol.format.WFS({featureNS:"fiware",featureType:'fw_core',schemaLocation:"http://www.opengis.net/wfs \
http://schemas.opengis.net/wfs/1.1.0/WFS-transaction.xsd \
http://192.168.4.33:9090/geoserver/grp/wfs/DescribeFeatureType?typename=fiware:fw_core"});
function addInteraction() {
draw = new ol.interaction.Draw({
features: featureOverlay.getFeatures(),
type: (typeSelect.value)
});
draw.on('drawend', function(evt) {
var feature = evt.feature;
feature.set('geometry', feature.getGeometry());
var node = format.writeTransaction([feature], null, null, {
gmlOptions: {srsName: "EPSG:3857"},
featureNS: "fiware",
featureType: "fiware:fw_core"
});
$.ajax({
type: "POST",
url: "http://192.168.4.33:9090/geoserver/wfs",
data: new XMLSerializer().serializeToString(node),
contentType: 'text/xml',
success: function(data) {
var result = format.readTransactionResponse(data);
feature.setId(result.insertIds[0]);
},
error: function(e) {
var errorMsg = e? (e.status + ' ' + e.statusText) : "";
bootbox.alert('Error saving this feature to GeoServer.<br><br>'
+ errorMsg);
},
context: this
});
});
map.addInteraction(draw);
}
Also, when defining a vector layer on Geoserver, on the publication tab, you must determine which column you are using as the geometry column.
Another thing, depending on the version of OpenLayers 3, you may need node.impl instead of node in this line of code:
new XMLSerializer().serializeToString(node.impl)
Hope this helps!