topic Re: how to query map knowing map layer name (not id) in ArcGIS API for Silverlight Questions

how to query map knowing map layer name (not id)

ThaoNguyen — Mon, 15 Nov 2010 18:50:58 GMT

HI,
I have a map layer name, but don't have map id. How can I write the QueryTask that is needed to query the map? How to get layer id if I know map layer name? Please help! Thank you so much!!

Below is my code:

QueryTask queryTask = new QueryTask(MapURL); //I don't know the layer ID, therefore, cannot do MapURL + "/<layerid>")
                queryTask.Failed += QueryTask_Failed;
                queryTask.ExecuteCompleted += QueryTask_ExecuteCompleted;

                // Specify fields to return from query
                Query query = new ESRI.ArcGIS.Client.Tasks.Query();
                query.OutFields.Add("*");
                query.Where = "0=0";

                // Return geometry with result features
                query.ReturnGeometry = true;
                queryTask.ExecuteAsync(query);

Re: how to query map knowing map layer name (not id)

JenniferNery — Mon, 15 Nov 2010 19:12:22 GMT

Is there a reason why you don't want to set the ID of the layer? You can get the layer based on ID or index.
Map.Layers[LayerID] or Map.Layers[index]

Re: how to query map knowing map layer name (not id)

ThaoNguyen — Tue, 16 Nov 2010 11:17:11 GMT

Is there a reason why you don't want to set the ID of the layer? You can get the layer based on ID or index.
Map.Layers[LayerID] or Map.Layers[index]

At this point, the map query is NOT executed yet; therefore, I don't have anything from the Map object, no layers, no features. I only know layer name which is passed to me by another means, not after drawing the map.
My queryTask URL should have something like http://myMachineName/ArcGIS/rest/services/MapServer/MyMap/LayerID
and I don't have layerID. Is there another way to construct QueryTask?

Thanks!

Re: how to query map knowing map layer name (not id)

DominiqueBroux — Tue, 16 Nov 2010 11:55:20 GMT

One option is you to include an ArcGISDynamicMapService in your map. Then, the 'Layers' property of this ArcGISDynamicMapService is giving you an array with the layer IDs, names, ...

If you don't want to include such a layer in your map, you can request yourself the mapserver endpoint and deserialize the result. Example of mapserver url : http://services.arcgisonline.com/ArcGIS/rest/services/Demographics/USA_Median_Age/MapServer?f=pjson

Re: how to query map knowing map layer name (not id)

ThaoNguyen — Tue, 16 Nov 2010 12:46:16 GMT

One option is you to include an ArcGISDynamicMapService in your map. Then, the 'Layers' property of this ArcGISDynamicMapService is giving you an array with the layer IDs, names, ...

If you don't want to include such a layer in your map, you can request yourself the mapserver endpoint and deserialize the result. Example of mapserver url : http://services.arcgisonline.com/ArcGIS/rest/services/Demographics/USA_Median_Age/MapServer?f=pjson

I do have ArcGISDynamicMapService in my map, but at this point, I have not run the query to get the map layers yet. My code is run after the wpf map page is loaded (it is inside the xx_loaded method). Map.Layers will be null. Hope I'm clear now.

Re: how to query map knowing map layer name (not id)

JenniferNery — Tue, 16 Nov 2010 12:49:37 GMT

Oh you don't mean x:Name?

If you mean name defined in the service, you can probably keep them in a dictionary (if you know that names will be unique), with URL as the value. You can add to the dictionary as each layer is initialized.

For the main layer, you can use MapName.
http://help.arcgis.com/en/webapi/silverlight/apiref/ESRI.ArcGIS.Client~ESRI.ArcGIS.Client.ArcGISDynamicMapServiceLayer~MapName.html

For the sub layers, you can use LayerInfo.Name and append the sub layer ID to the main layer's URL.
http://help.arcgis.com/en/webapi/silverlight/apiref/ESRI.ArcGIS.Client~ESRI.ArcGIS.Client.LayerInfo~Name.html

For FeatureLayer, it's similar.
http://help.arcgis.com/en/webapi/silverlight/apiref/ESRI.ArcGIS.Client~ESRI.ArcGIS.Client.FeatureService.FeatureLayerInfo_members.html

These information are available after the layer has initialized.

Re: how to query map knowing map layer name (not id)

ThaoNguyen — Tue, 16 Nov 2010 13:16:57 GMT

Oh you don't mean x:Name?

If you mean name defined in the service, you can probably keep them in a dictionary (if you know that names will be unique), with URL as the value. You can add to the dictionary as each layer is initialized.

For the main layer, you can use MapName.
http://help.arcgis.com/en/webapi/silverlight/apiref/ESRI.ArcGIS.Client~ESRI.ArcGIS.Client.ArcGISDynamicMapServiceLayer~MapName.html

For the sub layers, you can use LayerInfo.Name and append the sub layer ID to the main layer's URL.
http://help.arcgis.com/en/webapi/silverlight/apiref/ESRI.ArcGIS.Client~ESRI.ArcGIS.Client.LayerInfo~Name.html

For FeatureLayer, it's similar.
http://help.arcgis.com/en/webapi/silverlight/apiref/ESRI.ArcGIS.Client~ESRI.ArcGIS.Client.FeatureService.FeatureLayerInfo_members.html

These information are available after the layer has initialized.

No, I didn't mean x:Name.
Basically, the name of the layer is given to me. This is retrieved from data, not from map at all. Knowing the layer name, now, I want to query the map layer so that I can get the regions of that layer. For instance, my layer name is USRegions which has 9 features. I want to run a QueryTask that somehow takes my "USRegions" and after the query is run, it gives me 9 features. If I knew map layer ID, that would solve the problem, but unfortunately, I don't have layer id.

Re: how to query map knowing map layer name (not id)

ThaoNguyen — Tue, 16 Nov 2010 13:18:30 GMT

One option is you to include an ArcGISDynamicMapService in your map. Then, the 'Layers' property of this ArcGISDynamicMapService is giving you an array with the layer IDs, names, ...

If you don't want to include such a layer in your map, you can request yourself the mapserver endpoint and deserialize the result. Example of mapserver url : http://services.arcgisonline.com/ArcGIS/rest/services/Demographics/USA_Median_Age/MapServer?f=pjson

Do you have an example in C# how to get layerID using REST API?

Re: how to query map knowing map layer name (not id)

DominiqueBroux — Tue, 16 Nov 2010 13:32:07 GMT

I do have ArcGISDynamicMapService in my map, but at this point, I have not run the query to get the map layers yet. My code is run after the wpf map page is loaded (it is inside the xx_loaded method). Map.Layers will be null. Hope I'm clear now.

I don't understand why Map.layers is null if you do have an ArcGISDynamicMapService inside it. You should at least have this layer in Map.Layers?

That being said, this will not help you because at this moment the layer is not yet initialized so the sublayers are not yet known.

You could put your code in the 'Initialized' event of the layer. At this moment, the LayerInfo array will be initialized.

Re: how to query map knowing map layer name (not id)

ThaoNguyen — Tue, 16 Nov 2010 14:27:07 GMT

I don't understand why Map.layers is null if you do have an ArcGISDynamicMapService inside it. You should at least have this layer in Map.Layers?

That being said, this will not help you because at this moment the layer is not yet initialized so the sublayers are not yet known.

You could put your code in the 'Initialized' event of the layer. At this moment, the LayerInfo array will be initialized.

Sorry, my bad, I was not clear.

In order to draw a map, you have to tell the map where the map service is or what map service you want to connect to, right?

Here is what I have in xaml:
<esri:Map x:Uid="mapId" x:Name="MainMap"
                  Margin="0"
                  Extent="-150.773,5.7054,-51.813,67.5554"
                  MouseRightButtonDown="MainMap_MouseRightButtonDown"
                  VerticalAlignment="Top"
                  ExtentChanged="MainMap_ExtentChanged"
                  >
            <esri:Map.Layers>
                <esri:ArcGISDynamicMapServiceLayer x:Uid="dynMapSvcId" ID="BigMap" Url="" />
                
                <esri:GraphicsLayer x:Uid="graphicLayerId" ID="ResultMap" Opacity="0.7"/>

            </esri:Map.Layers>

        </esri:Map>

Code behind:
public MyClass()
        {
            InitializeComponent();
        }

private void MyClass_Loaded(object sender, RoutedEventArgs e)
        {
                QueryTask queryTask = new QueryTask(MapURL);
                queryTask.Failed += QueryTask_Failed;
                queryTask.ExecuteCompleted += QueryTask_ExecuteCompleted;

                // Specify fields to return from query
                Query query = new ESRI.ArcGIS.Client.Tasks.Query();
                query.OutFields.Add("*");
                query.Where = "0=0";
                // Return geometry with result features
                query.ReturnGeometry = true;
                queryTask.ExecuteAsync(query);
}
The "MapURL" variable should have something like this: http://machineName/ArcGIS/rest/services/MyMapServiceName/MapServer/LayerID

I don't have LayerID in order to pass in the URL, but I have the layer name.
So, basically, the map is not drawing yet in this method. The layer I meant was the layer from the map service Website. So, Map.Layers should not be null. You are correct!! But the ID for the layer from xaml is not what I'm looking for. I want the ID of the layer when I view the map service from the URL. Sorry for not being clear!

So, I think using json to get layer ID is one way, but I don't know how to do it. Do you have an example in C# code how to do it? I tried to pass in the url of "http://machineName/ArcGIS/rest/services/MyMapServiceName/MapServer/?f=json" to the code above but the query failed with System.Net.WebException: The remote server returned an error: (400) Bad Request.
I guess I didn't do it right.

Re: how to query map knowing map layer name (not id)

DominiqueBroux — Sat, 11 Dec 2021 21:46:12 GMT

 
<esri:ArcGISDynamicMapServiceLayer x:Uid="dynMapSvcId" ID="BigMap" Url="" />

My understanding is that you know the url of your map service, so it should be:

 
<esri:ArcGISDynamicMapServiceLayer x:Uid="dynMapSvcId" ID="BigMap" Url="http://<server>/ArcGIS/rest/services/<mapService>" />

then you can add an Initialized event handler:

 
<esri:ArcGISDynamicMapServiceLayer x:Uid="dynMapSvcId" ID="BigMap" Url="http://<server>/ArcGIS/rest/services/<mapService>" 
Initialized="BigMap_Initialized" />

and in the event handler you can use the LayerInfo array to define which layerID you want to work with and make your query.

Note that instead of using a graphicslayer and a query, you could use a feature layer which is basically doing that without any code from you. You just have to initialize the Url of the feature layer which is also something like http://<server>/ArcGIS/rest/services/<mapService>/LayerID

Re: how to query map knowing map layer name (not id)

JenniferNery — Tue, 16 Nov 2010 15:30:24 GMT

How about initializing the ArcGISDynamicMapServiceLayer in code, subscribe to its Initialized event, call Initialize(). At it's Initialized event handler, retrieve the sublayer Name and ID information. Save this info onto a dictionary with Name as Key and ID as value.

Once you are given the sub layer name, you can get the corresponding ID from this dictionary and append it to the ArcGISDynamicMapServiceLayer URL so you can run your query against it.

The ArcGISDynamicMapServiceLayer in this case is not added to your map but is Initialized and used to get its sub layers.

Re: how to query map knowing map layer name (not id)

ThaoNguyen — Sat, 11 Dec 2021 21:46:15 GMT

 
<esri:ArcGISDynamicMapServiceLayer x:Uid="dynMapSvcId" ID="BigMap" Url="" />
 
My understanding is that you know the url of your map service, so it should be:
 
<esri:ArcGISDynamicMapServiceLayer x:Uid="dynMapSvcId" ID="BigMap" Url="http://<server>/ArcGIS/rest/services/<mapService>" />
then you can add an Initialized event handler:
 
<esri:ArcGISDynamicMapServiceLayer x:Uid="dynMapSvcId" ID="BigMap" Url="http://<server>/ArcGIS/rest/services/<mapService>" 
Initialized="BigMap_Initialized" />
and in the event handler you can use the LayerInfo array to define which layerID you want to work with and make your query.

Note that instead of using a graphicslayer and a query, you could use a feature layer which is basically doing that without any code from you. You just have to initialize the Url of the feature layer which is also something like http://<server>/ArcGIS/rest/services/<mapService>/LayerID

The problem I have now is I do not have layerID (which is a number); but I have a layer name. I do not know map service until someone passes it to me; therefore, I want to put it in code. In addition, it is changed... Anyway, that is not important, what I want is I want to run a queryTask that I can pass in layer name, not layer id which I do not have.

Re: how to query map knowing map layer name (not id)

DaveTimmins — Tue, 16 Nov 2010 17:31:08 GMT

Hi,

something like this?

int GetLayerID(string layerName)
        {
            var client = new WebClient();
            client.DownloadStringCompleted += (sender, args) =>
            {
                string json = args.Result;
                foreach (var layer in JObject.Parse(json)["layers"].Children())
                {
                    if (string.Equals((string)layer["name"], layerName, StringComparison.OrdinalIgnoreCase))
                        return (int)layer["id"];
                }
                throw new InvalidOperationException(string.Format("A layer with the name '{0}' was not found in the MXD.", layerName));
            };
            string uri = "your map server url" + "?f=json";
            client.DownloadStringAsync(new Uri(uri));
        }

Re: how to query map knowing map layer name (not id)

ThaoNguyen — Tue, 16 Nov 2010 17:47:04 GMT

Hi,

something like this?

int GetLayerID(string layerName)
        {
            var client = new WebClient();
            client.DownloadStringCompleted += (sender, args) =>
            {
                string json = args.Result;
                foreach (var layer in JObject.Parse(json)["layers"].Children())
                {
                    if (string.Equals((string)layer["name"], layerName, StringComparison.OrdinalIgnoreCase))
                        return (int)layer["id"];
                }
                throw new InvalidOperationException(string.Format("A layer with the name '{0}' was not found in the MXD.", layerName));
            };
            string uri = "your map server url" + "?f=json";
            client.DownloadStringAsync(new Uri(uri));
        }

Thank you so much!! That is what I'm looking for.
BTW, is the space name for JObject Newtonsoft.Json.Linq? Just want to double check before I add the dll that contains this object to my VStudio project.

Re: how to query map knowing map layer name (not id)

DaveTimmins — Tue, 16 Nov 2010 18:31:24 GMT

Yes that's correct. You'll need the Newtonsoft.Json.Silverlight library.

Re: how to query map knowing map layer name (not id)

ThaoNguyen — Thu, 18 Nov 2010 13:29:02 GMT

Hi,

something like this?

int GetLayerID(string layerName)
        {
            var client = new WebClient();
            client.DownloadStringCompleted += (sender, args) =>
            {
                string json = args.Result;
                foreach (var layer in JObject.Parse(json)["layers"].Children())
                {
                    if (string.Equals((string)layer["name"], layerName, StringComparison.OrdinalIgnoreCase))
                        return (int)layer["id"];
                }
                throw new InvalidOperationException(string.Format("A layer with the name '{0}' was not found in the MXD.", layerName));
            };
            string uri = "your map server url" + "?f=json";
            client.DownloadStringAsync(new Uri(uri));
        }

For those who are interested, another way to get the json (without waiting for the event to be completed)

var client = new System.Net.WebClient();
try
{
using (StreamReader reader = new StreamReader(client.OpenRead("your map url here" + "?f=json")))
string json = reader.ReadToEnd();

//do get layer Id like Dave posted
foreach (var layer in JObject.Parse(json)["layers"].Children())
                {
                    if (string.Equals((string)layer["name"], layerName, StringComparison.OrdinalIgnoreCase))
                        return (int)layer["id"];
                }

}
catch (Exception ex)
{
//your code here
}