Creates a new FeatureLayer containing features from the ServiceChildLayer which match the criteria in the SQL WHERE Clause.

Namespace:  ESRI.ArcGISExplorer.Mapping

Assembly:  ESRI.ArcGISExplorer (in ESRI.ArcGISExplorer.dll) Version: 2.0.0.1500 (2.0.0.1500)

Syntax

C#
public FeatureLayer Query(
	string whereClause
)
Visual Basic (Declaration)
Public Function Query ( _
	whereClause As String _
) As FeatureLayer

Parameters

whereClause
Type: System..::.String

A string containing the SQL WHERE clause to be used in the query on this ServiceChildLayer.

Return Value

A new Mapping.FeatureLayer containing the subset of features from the ServiceChildLayer which match the criteria in the SQL WHERE Clause.

Remarks

This method applies a query to the features within a ServiceChildLayer. All features matching the criteria specified in the query are returned in a new FeatureLayer. The query executed by the method follows the standard SQL structure of SELECT * FROM WHERE. It is the criteria which follow "WHERE" that must be specified in the whereClause parameter, for example "NAME = 'San Diego'".

Prior to calling the Query method of a ServiceChildLayer there are a number of other methods and properties which should be used to ensure the eventual call to the Query method will return a successful result:

  • ServiceLayer.CanQuery: This value should be accessed first, prior to any members on the ServiceChildLayers which make up the ServiceLayer. If this value is false any attempt to access the query related members of a constituent ServiceChildLayer will result in an ExplorerException.
  • ServiceChildLayer.CanQuery: If this value is false any attempt to access the query related members on this ServiceChildLayer will result in an ExplorerException.
  • ServiceChildLayer.QueryFeatureLimit: This value should be used in conjunction with QueryFeatureCount below to ensure that the WHERE clause used in the Query method call does not produce a result set which exceeds this server-side setting.
  • ServiceChildLayer.QueryFeatureCount: Informs you how many features would be returned in response to a given query without needing to return the actual result set to the client application. If this value is greater than the QueryFeatureLimit value above, the query should be modified and compared to the QueryFeatureLimit, repeatedly if necessary, until QueryFeatureCount is less than the QueryFeatureLimit.

Once a successful query has been established via the QueryFeatureLimit property and QueryFeatureCount method, that same query should be used when calling the actual Query method. The Query method will return a new FeatureLayer on which the Connect method must be called prior to any attempt to access certain members on that FeatureLayer (GeometryType, PopupProperties and Table). The DataSourceType of the layer will be InMemory.

Version Information: This member is supported from version 2.0.0.1500.

Examples

The code below demonstrates the process of connecting to a ServiceLayer and confirming that both the top level ServiceLayer and a specific ServiceChildLayer will support queries before then accessing the Columns, QueryFeatureLimit, and QueryFeatureCount members to ensure a valid query is executed against the ServiceChildLayer via the Query method. Finally, the example connects to the FeatureLayer datasource and gets the number of rows in the result FeatureLayer table.
CopyC#
{

  //Create a new ServiceConnectionProperties instance and populate with connection information
  ServiceConnectionProperties serviceConnProps = new ServiceConnectionProperties(ServiceType.MapServer,
      new Uri("http://sampleserver1.arcgisonline.com/ArcGIS/services/Demographics"),
      "/ESRI_Census_USA");

  //Create a new ServiceLayer instance passing in the ServiceConnectionProperties 
  ServiceLayer serviceLayer = new ServiceLayer(serviceConnProps);

  //Check the ServiceLayer can Connect
  if (!serviceLayer.Connect())
    return;

  //Check this ServiceLayer supports queries
  if (!serviceLayer.CanQuery)
    return;

  //Get the "states" ServiceChildLayer on which we want to execute a query
  ServiceChildLayer serviceChildLayerStates = serviceLayer.FindByName("states") as ServiceChildLayer;

  //Check this ServiceChildlayer supports queries
  if (!serviceChildLayerStates.CanQuery)
    return;

  //Get the collection of columns for the ServiceChildLayer
  ColumnCollection columns = serviceChildLayerStates.Columns;

  //Create the WHERE clause
  string whereClause = string.Empty;

  //Check each column until the alias matches the intended query field
  foreach (Column column in columns)
  {
    //Use column members to confirm the the AliasName and data type
    if (column.AliasName == "POP2007" & column.Type == ColumnType.Integer)
    {
      //Populate the WHERE clause with matched column name, operator and value
      whereClause = column.Name + " > 10000000";
      break;
    }
  }

  //Check the WHERE clause
  if (whereClause == string.Empty)
    return;

  //Get the maximum number of records returnable from the service
  int queryFeatureLimit = serviceChildLayerStates.QueryFeatureLimit;

  //Get the number of features matching the WHERE clause
  int queryFeatureCount = serviceChildLayerStates.QueryFeatureCount(whereClause);

  //IMPORTANT: Check the feature count is not greater than the feature limit
  if (!(queryFeatureCount <= queryFeatureLimit))
    return;

  //Execute the Query method to get a new FeatureLayer containing the results
  FeatureLayer featureLayer = serviceChildLayerStates.Query(whereClause);

  //The FeatureLayer method must be called to access all FeatureLayer members
  if (!featureLayer.Connect())
    return;

  //Implement code to work with FeatureLayer (in this case get the number of rows)
  int numberOfResultFeatures = featureLayer.Table.GetRows().Count;

}
CopyVB.NET
'Create a new ServiceConnectionProperties instance and populate with connection information
Dim serviceConnProps As New ServiceConnectionProperties( _
ServiceType.MapServer, _
New Uri("http://sampleserver1.arcgisonline.com/ArcGIS/services/Demographics"), _
"/ESRI_Census_USA")

'Create a new ServiceLayer instance passing in the ServiceConnectionProperties 
Dim serviceLayer1 As New ServiceLayer(serviceConnProps)

'Check the ServiceLayer can Connect
If Not serviceLayer1.Connect() Then
  Return
End If

'Check this ServiceLayer supports queries  
If Not serviceLayer1.CanQuery Then
  Return
End If

'Get the "states" ServiceChildLayer on which we want to execute a query  
Dim serviceChildLayerStates As ServiceChildLayer = TryCast(serviceLayer1.FindByName("states"), ServiceChildLayer)

'Check this ServiceChildlayer supports queries  
If Not serviceChildLayerStates.CanQuery Then
  Return
End If

'Get the collection of columns for the ServiceChildLayer  
Dim columns As ColumnCollection = serviceChildLayerStates.Columns

'Create the WHERE clause  
Dim whereClause As String = String.Empty

'Check each column until the alias matches the intended query field  
For Each column As Column In columns

  'Use column members to confirm the the AliasName and data type  
  If column.AliasName = "POP2007" And column.Type = ColumnType.[Integer] Then

    'Populate the WHERE clause with matched column name, operator and value  
    whereClause = column.Name + " > 10000000"
    Exit For

  End If

Next

'Check the WHERE clause  
If whereClause = String.Empty Then
  Return
End If

'Get the maximum number of records returnable from the service  
Dim queryFeatureLimit As Integer = serviceChildLayerStates.QueryFeatureLimit

'Get the number of features matching the WHERE clause  
Dim queryFeatureCount As Integer = serviceChildLayerStates.QueryFeatureCount(whereClause)

'IMPORTANT: Check the feature count is not greater than the feature limit  
If Not (queryFeatureCount <= queryFeatureLimit) Then
  Return
End If

'Execute the Query method to get a new FeatureLayer containing the results  
Dim featureLayer As FeatureLayer = serviceChildLayerStates.Query(whereClause)

'The FeatureLayer method must be called to access all FeatureLayer members  
If Not featureLayer.Connect() Then
  Return
End If

'Implement code to work with FeatureLayer (in this case get the number of rows)  
Dim numberOfResultFeatures As Integer = featureLayer.Table.GetRows().Count

See Also