[GIS] How to navigate the REST endpoints and retrieve Field information programatically

arcgis-javascript-apiarcgis-rest-apijavascriptrest

I'm adding a Dynamic Map Service to an ArcGIS Server JavaScript API map, and I need to get hold of each component layer and its fields, so I can run a query.

See the sample ArcGIS Server services directory at http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/HomelandSecurity/operations/MapServer

If you open this URL in a browser you can see the list of available layers (0,1,2) and each layer's fields.

How can I retrieve the list of fields programatically, within a JavaScript function? The code snippet below shows how to retrieve the layer endpoints, but I can't see how to get to the fields.

(One option is to add the layers as Feature Layers, but I'd prefer to avoid this if possible).

var url = "http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/HomelandSecurity/operations/MapServer/";
var dynLayer = new esri.layers.ArcGISDynamicMapServiceLayer(url);
map.addLayer(dynLayer);

dojo.connect(dynLayer, "onLoad", function() {
   var infos = dynLayer.layerInfos;
   for (var i = 0; i <= infos.length - 1; i++) {
       var layerId = infos[i].id;
       var restEndPoint = url + layerId;
       //restEndPoint is the layer's URL - how can I retrieve its fields?
   }
});

Thanks,
Steve (cross-posted to the ArcGIS Server forum)

Best Answer

Use esri.request() to hit each layer's REST endpoint to get info about fields. Here's a simple example:

<html>
  <head>
    <script type="text/javascript">var djConfig = {parseOnLoad: true};</script>
    <script type="text/javascript" src="http://serverapi.arcgisonline.com/jsapi/arcgis/?v=2.4"></script>
    <script type="text/javascript">
      dojo.require("esri.map");
      // var service_url = 'http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Hurricanes/NOAA_Tracks_1851_2007/MapServer/layers';
      var service_url = 'http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Fire/Sheep/MapServer/layers';

      function init() {
        esri.request({
          url: service_url,
          content: { f: 'json' },
          callbackParamName: 'callback',
          load: processServiceInfo,
          error: errorHandler
        });
      }
      // Runs once
      function processServiceInfo(info) {
        console.log('svc info: ', info);
        dojo.byId('info').innerHTML = '';
        dojo.forEach(info.layers, function(lyr) {

          // Add a new div for each Layer
          var lyr_div = dojo.create('div', { 
            id: 'layer_' + lyr.id,
            innerHTML: '<strong>Layer: ' + lyr.name + '</strong><br />'
          }, dojo.byId('info'));

          dojo.forEach(lyr.fields, function(field) {
            lyr_div.innerHTML += 'Name: ' + field.name + '; Alias: ' + field.alias + '<br />';
          });
        });
      }

      function errorHandler(err) {
        console.log('error: ', err);
      }

      dojo.ready(init);
    </script>
  </head>
  <body>
    <div id="info">field names and aliases will show up here.</div>
  </body>
</html>

That code uses v2.0 of the API but the same thing will work at 2.3 or 2.4. I originally posted in the Esri JS API forum.

Edit: Updated to handle all layers in a service. The code also now uses version 2.4 of the API.

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