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Distinct Query?

RobChouinard

Why is there no "Return Distinct Values" in Query? Am I missing it somewhere?

I am running ArcGIS Server 10.1.1 and Silverlight API 3.1. On the Query form for a REST service layer there is a "Return Distinct Values" and works as expected. It is exactly what I am looking for. As a workaround I have views made for about a dozen fields. It would be really nice to have this flexibility especially since the feature is already on the server side.

Rob

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Accepted answers

RobChouinard

Well I wrote my own class to handle this and I am here to share. Is there a better place to share code like this?

Thanks to ESRI for making this easier by providing ArcGISWebClient and FeatureSet.FromJson() in the SDK.

QueryDistinctTask.cs

/**  * Created by Rob Chouinard  *   * Free to use and destroy!  * Requires Silverlight API 3.1+ and ArcGIS Server 10.1 SP1+  * Use is similar to ESRI.ArcGIS.Client.Tasks.QueryTask  **/  using System; using System.ComponentModel; using System.Collections.Generic; using ESRI.ArcGIS.Client; using ESRI.ArcGIS.Client.Tasks;  namespace ESRI.ArcGIS.Extensions {     public class QueryDistinctTask     {         ArcGISWebClient webClient = null;          /// <summary>         /// Initializes a new instance of the <seealso cref="QueryDistinctTask"/> class.         /// </summary>         /// <param name="Url">The URL of the task.</param>         public QueryDistinctTask(string Url = "")         {             this.Url = Url;         }          #region Properties         /// <summary>         /// If true, adds a timestamp parameter ("_ts") to the request to prevent it from being loaded from the browser's cache.         /// </summary>         public bool DisableClientCaching          {             get { return disableClientCaching; }              set             {                 if (disableClientCaching != value)                 {                     disableClientCaching = value;                     OnPropertyChanged("DisableClientCaching");                 }             }         }         bool disableClientCaching = false;          /// <summary>         /// Gets a value that indicates whether a Web request is in progress.         /// </summary>         public bool IsBusy         {             get             {                 if (webClient != null)                     return webClient.IsBusy;                 else                     return false; ;             }         }          /// <summary>         /// Gets or sets the URL to proxy the request through.           /// </summary>         public string ProxyURL         {             get { return proxyURL; }             set             {                 if (proxyURL != value)                 {                     proxyURL = value;                     OnPropertyChanged("ProxyURL");                 }             }         }         string proxyURL;          /// <summary>         /// Gets or sets the last query result.         /// </summary>         public FeatureSet LastResult          {             get { return lastResult; }             private set             {                 if (lastResult != value)                 {                     lastResult = value;                     OnPropertyChanged("LastResult");                 }             }         }         FeatureSet lastResult;          /// <summary>         /// Gets or sets the URL of the task.           /// </summary>         public string Url         {             get { return url; }             set             {                 if (url != value)                 {                     url = value;                     OnPropertyChanged("Url");                 }             }         }         string url;         #endregion          #region Events         /// <summary>         /// Occurs when the query completes.         /// </summary>         public event EventHandler<QueryDistinctEventArgs> ExecuteCompleted;          /// <summary>         /// Occurs when the query completes and fails.         /// </summary>         public event EventHandler<AsyncCompletedEventArgs> Failed;          /// <summary>         /// Occurs when a property value changes.         /// </summary>         public event PropertyChangedEventHandler PropertyChanged;         #endregion          #region Public Methods         /// <summary>         /// Cancels a pending asynchronous operation.         /// </summary>         public void CancelAsync()         {             if (webClient != null)                 webClient.CancelAsync();         }          /// <summary>         /// Executes a query against an ArcGIS Server map layer. The result is returned as a FeatureSet. If the query is successful, the <seealso cref="QueryDistinctTask.ExecuteCompleted"/> event is raised with the result. A FeatureSet contains an array of Graphic features without geometery. This array will not be populated if no results are found.         /// </summary>         /// <param name="query">Specifies the attributes filter of the query.</param>         /// <param name="userToken">A user-defined object that is passed to the method invoked when the asynchronous operation completes.</param>         public void ExecuteAsync(QueryDistinct query, object userToken = null)         {             webClient = new ArcGISWebClient();             webClient.DisableClientCaching = DisableClientCaching;             webClient.ProxyUrl = ProxyURL;             webClient.DownloadStringCompleted += DownloadStringCompleted;              string extendedUrl = Url;             if (!Url.EndsWith("/"))                 extendedUrl += "/";             extendedUrl += "query";              if (!webClient.IsBusy)                 webClient.DownloadStringAsync(new Uri(extendedUrl), GetParameters(query), ArcGISWebClient.HttpMethods.Auto, userToken);             else             {                 throw new Exception("The web client is busy processing it's current task. \nWait for the current process to complete before processing another request.");             }         }         #endregion          #region Private Methods         IDictionary<string, string> GetParameters(QueryDistinct query)         {             IDictionary<string, string> parameters = new Dictionary<string, string>();             if (query.Where != null && query.Where.Length > 0)                 parameters.Add("where", query.Where);             else if (query.Text != null)                 parameters.Add("text", query.Text);              parameters.Add("outFields", string.Join(",", query.OutFields)); // Return all of the fields.             parameters.Add("returnGeometry", "false"); // Do not include the geometry coordinate values.             parameters.Add("returnDistinctValues", "true"); // Since that is what we are after.             parameters.Add("f", "json"); // Get the results back in the 'pretty' JSON format.              return parameters;         }          void DownloadStringCompleted(object sender, ArcGISWebClient.DownloadStringCompletedEventArgs e)         {             if (e.Error != null || e.Cancelled)             {                 OnFailed(new AsyncCompletedEventArgs(e.Error, e.Cancelled, e.UserState));                 return;             }              if (e.Cancelled)                 return;              try             {                 FeatureSet featureSet = FeatureSet.FromJson(e.Result);                 int count = featureSet.Features.Count;                 lastResult = featureSet;                 QueryDistinctEventArgs queryEventArgs = new QueryDistinctEventArgs(featureSet)                 {                     UserState = e.UserState                 };                 OnExecuteCompleted(queryEventArgs);             }             catch (Exception)             {                 try                 {                     ServiceException se = ServiceException.FromJson(e.Result);                     OnFailed(                         new AsyncCompletedEventArgs(se, e.Cancelled, e.UserState));                 }                 catch (Exception)                 {                     OnFailed(                     new AsyncCompletedEventArgs(                         new Exception("Failed to parse featureSet from json.\nCheck your URL and query."),                         e.Cancelled,                         e.UserState)                     );                 }             }         }          void OnFailed(AsyncCompletedEventArgs asyncCompletedEventArgs)         {             if (Failed != null)                 Failed(this, asyncCompletedEventArgs);         }          void OnPropertyChanged(string Name)         {             if (PropertyChanged != null)                 PropertyChanged(this, new PropertyChangedEventArgs(Name));         }          void OnExecuteCompleted(QueryDistinctEventArgs queryEventArgs)         {             if (ExecuteCompleted != null)                 ExecuteCompleted(this, queryEventArgs);         }         #endregion     }      public class QueryDistinct     {         public OutFields OutFields { get; set; }         public string Text { get; set; }         public string Where { get; set; }          public QueryDistinct()         {             OutFields = new OutFields();         }     }      public class QueryDistinctEventArgs : EventArgs     {         public FeatureSet FeatureSet { get; private set; }         public object UserState { get; set; }          public QueryDistinctEventArgs(FeatureSet featureSet)         {             FeatureSet = featureSet;         }     } }

QueryDistinctTask.zip

All comments

DominiqueBroux

The 'returnDistinctValues' option has been added recently at the server side (10.1 SP1) and is not yet exposed by the Silverlight API.
We'll try to add this capability in a future version.

Thanks for sharing your workaround, might be useful for others having the same need.

RobChouinard

/**  * Created by Rob Chouinard  *   * Free to use and destroy!  * Requires Silverlight API 3.1+ and ArcGIS Server 10.1 SP1+  * Use is similar to ESRI.ArcGIS.Client.Tasks.QueryTask  **/  using System; using System.ComponentModel; using System.Collections.Generic; using ESRI.ArcGIS.Client; using ESRI.ArcGIS.Client.Tasks;  namespace ESRI.ArcGIS.Extensions {     public class QueryDistinctTask     {         ArcGISWebClient webClient = null;          /// <summary>         /// Initializes a new instance of the <seealso cref="QueryDistinctTask"/> class.         /// </summary>         /// <param name="Url">The URL of the task.</param>         public QueryDistinctTask(string Url = "")         {             this.Url = Url;         }          #region Properties         /// <summary>         /// If true, adds a timestamp parameter ("_ts") to the request to prevent it from being loaded from the browser's cache.         /// </summary>         public bool DisableClientCaching          {             get { return disableClientCaching; }              set             {                 if (disableClientCaching != value)                 {                     disableClientCaching = value;                     OnPropertyChanged("DisableClientCaching");                 }             }         }         bool disableClientCaching = false;          /// <summary>         /// Gets a value that indicates whether a Web request is in progress.         /// </summary>         public bool IsBusy         {             get             {                 if (webClient != null)                     return webClient.IsBusy;                 else                     return false; ;             }         }          /// <summary>         /// Gets or sets the URL to proxy the request through.           /// </summary>         public string ProxyURL         {             get { return proxyURL; }             set             {                 if (proxyURL != value)                 {                     proxyURL = value;                     OnPropertyChanged("ProxyURL");                 }             }         }         string proxyURL;          /// <summary>         /// Gets or sets the last query result.         /// </summary>         public FeatureSet LastResult          {             get { return lastResult; }             private set             {                 if (lastResult != value)                 {                     lastResult = value;                     OnPropertyChanged("LastResult");                 }             }         }         FeatureSet lastResult;          /// <summary>         /// Gets or sets the URL of the task.           /// </summary>         public string Url         {             get { return url; }             set             {                 if (url != value)                 {                     url = value;                     OnPropertyChanged("Url");                 }             }         }         string url;         #endregion          #region Events         /// <summary>         /// Occurs when the query completes.         /// </summary>         public event EventHandler<QueryDistinctEventArgs> ExecuteCompleted;          /// <summary>         /// Occurs when the query completes and fails.         /// </summary>         public event EventHandler<AsyncCompletedEventArgs> Failed;          /// <summary>         /// Occurs when a property value changes.         /// </summary>         public event PropertyChangedEventHandler PropertyChanged;         #endregion          #region Public Methods         /// <summary>         /// Cancels a pending asynchronous operation.         /// </summary>         public void CancelAsync()         {             if (webClient != null)                 webClient.CancelAsync();         }          /// <summary>         /// Executes a query against an ArcGIS Server map layer. The result is returned as a FeatureSet. If the query is successful, the <seealso cref="QueryDistinctTask.ExecuteCompleted"/> event is raised with the result. A FeatureSet contains an array of Graphic features without geometery. This array will not be populated if no results are found.         /// </summary>         /// <param name="query">Specifies the attributes filter of the query.</param>         /// <param name="userToken">A user-defined object that is passed to the method invoked when the asynchronous operation completes.</param>         public void ExecuteAsync(QueryDistinct query, object userToken = null)         {             webClient = new ArcGISWebClient();             webClient.DisableClientCaching = DisableClientCaching;             webClient.ProxyUrl = ProxyURL;             webClient.DownloadStringCompleted += DownloadStringCompleted;              string extendedUrl = Url;             if (!Url.EndsWith("/"))                 extendedUrl += "/";             extendedUrl += "query";              if (!webClient.IsBusy)                 webClient.DownloadStringAsync(new Uri(extendedUrl), GetParameters(query), ArcGISWebClient.HttpMethods.Auto, userToken);             else             {                 throw new Exception("The web client is busy processing it's current task. \nWait for the current process to complete before processing another request.");             }         }         #endregion          #region Private Methods         IDictionary<string, string> GetParameters(QueryDistinct query)         {             IDictionary<string, string> parameters = new Dictionary<string, string>();             if (query.Where != null && query.Where.Length > 0)                 parameters.Add("where", query.Where);             else if (query.Text != null)                 parameters.Add("text", query.Text);              parameters.Add("outFields", string.Join(",", query.OutFields)); // Return all of the fields.             parameters.Add("returnGeometry", "false"); // Do not include the geometry coordinate values.             parameters.Add("returnDistinctValues", "true"); // Since that is what we are after.             parameters.Add("f", "json"); // Get the results back in the 'pretty' JSON format.              return parameters;         }          void DownloadStringCompleted(object sender, ArcGISWebClient.DownloadStringCompletedEventArgs e)         {             if (e.Error != null || e.Cancelled)             {                 OnFailed(new AsyncCompletedEventArgs(e.Error, e.Cancelled, e.UserState));                 return;             }              if (e.Cancelled)                 return;              try             {                 FeatureSet featureSet = FeatureSet.FromJson(e.Result);                 int count = featureSet.Features.Count;                 lastResult = featureSet;                 QueryDistinctEventArgs queryEventArgs = new QueryDistinctEventArgs(featureSet)                 {                     UserState = e.UserState                 };                 OnExecuteCompleted(queryEventArgs);             }             catch (Exception)             {                 try                 {                     ServiceException se = ServiceException.FromJson(e.Result);                     OnFailed(                         new AsyncCompletedEventArgs(se, e.Cancelled, e.UserState));                 }                 catch (Exception)                 {                     OnFailed(                     new AsyncCompletedEventArgs(                         new Exception("Failed to parse featureSet from json.\nCheck your URL and query."),                         e.Cancelled,                         e.UserState)                     );                 }             }         }          void OnFailed(AsyncCompletedEventArgs asyncCompletedEventArgs)         {             if (Failed != null)                 Failed(this, asyncCompletedEventArgs);         }          void OnPropertyChanged(string Name)         {             if (PropertyChanged != null)                 PropertyChanged(this, new PropertyChangedEventArgs(Name));         }          void OnExecuteCompleted(QueryDistinctEventArgs queryEventArgs)         {             if (ExecuteCompleted != null)                 ExecuteCompleted(this, queryEventArgs);         }         #endregion     }      public class QueryDistinct     {         public OutFields OutFields { get; set; }         public string Text { get; set; }         public string Where { get; set; }          public QueryDistinct()         {             OutFields = new OutFields();         }     }      public class QueryDistinctEventArgs : EventArgs     {         public FeatureSet FeatureSet { get; private set; }         public object UserState { get; set; }          public QueryDistinctEventArgs(FeatureSet featureSet)         {             FeatureSet = featureSet;         }     } }

QueryDistinctTask.zip

RobChouinard

That help link is for ArcGIS Desktop. I have/do used LINQ to get distinct attribute values from a FeatureSet after querying all rows. This is ok for small to medium sized tables. For a very large table this won't do and is not practical. What I would like to do is utilize the new "Return Distinct Values" boolean variable when querying a REST MapService Layer as seen at the bottom of the page here: http://sampleserver6.arcgisonline.com/arcgis/rest/services/EmergencyFacilities/MapServer/0/query?where=1%3D1&text=&objectIds=&time=&geometry=&geometryType=esriGeometryEnvelope&inSR=&spatialRel=esriSpatialRelIntersects&relationParam=&outFields=organiz&returnGeometry=false&maxAllowableOffset=&geometryPrecision=&outSR=&returnIdsOnly=false&returnCountOnly=false&orderByFields=&groupByFieldsForStatistics=&outStatistics=&returnZ=false&returnM=false&gdbVersion=&returnDistinctValues=true&f=html

I plan on using ArcGISWebClient and FeatureSet.FromJson() to build a QueryDistinctTask class. If all goes well I will post it here.

What I really was looking for was an out of the box Silverlight API feature. Since it is a feature of ArcGIS Server why did ESRI not build this feature in Silverlight API? Or maybe I can't find it.

Rob

vipulsoni

Hi,

While developing an application I too faced the same hurdle and I guess my workaround might help you out.

First of all , as per the below link - Because you are selecting columns as a whole, you cannot restrict the SELECT to return only some of the columns in the corresponding table because the SELECT * syntax is hard-coded. For this reason, keywords, such as DISTINCT, ORDER BY, and GROUP BY, cannot be used in a SQL query in ArcGIS except when using subqueries.

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//00s50000002t000000

What I did is to get the results in a string Array and then apply distinct to the array....also further then I applied sort to it.
see the code pasted below it will give you an idea. but yes for getting the distinct through the API i am also unaware , this all i     posted is a workaround.
---------------------------------------------------------------------------------------------------

int f = 0;

foreach (var g in e.FeatureSet.Features)
                {

myStringArray = g.Attributes["Title"].ToString();
f++;
                    }

string[] unique = myStringArray.Distinct().ToArray();

Array.Sort(unique);

foreach(string s in unique)
                {

                 }

-------------------

also have a look at this post..

http://forums.esri.com/Thread.asp?c=213&f=2455&t=281270

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