The definition expression for the layer.
[Visual Basic .NET] Public Property DefinitionExpression As String
[C#] public string DefinitionExpression {get; set;}
[C++]
HRESULT get_DefinitionExpression(
BSTR* Expression
);
[C++]
HRESULT put_DefinitionExpression(
BSTR Expression
);
[C++]Parameters
Expression [out, retval] Expression is a parameter of type BSTR Expression [in] Expression is a parameter of type BSTR
Product Availability
Remarks
A DefinitionExpression can be set on a layer in order to limit layer features available for display or query. This expression can be also be set in the source map document as a definition query. An expression set in the LayerDescription will override one set for the layer in the source map. This only applies for the session state and does not replace the definition query set in the source map.
Let's look at some examples. You have a layer in your map that represents sales regions. The layer includes fields: REGIONS, SALES and MANAGER.
Example #1: In the source map the layer has a definition query, "REGION = North". No DefintionExpression is specified in LayerDescription. Only those features where REGION = North will be displayed in your map.
Example #2: In the source map the layer has a definition query, "REGION = ‘North’". You apply a DefinitionExpression in LayerDescription as "SALES > 1000". The LayerDescription DefinitionExpression overrides the definition query set in the source map. Only those features where SALES > 1000 will be displayed in your map.
If you wish to use the DefinitionExpression as a way of getting a subset of the features already filtered by the definition query in the map you will need to save the original expression and then add it to the new expression to form one compound expression, “REGION = ‘North’ AND SALES > 1000”. This will display map features that are belong to the North region and have sales over 1000.
Example #3: In the source map the layer has no definition query. You apply a DefinitionExpression in LayerDescription as "SALES > 1000". Only those features where SALES > 1000 will be displayed in your map.
The following MapServer methods will honor DefinitionExpression: Find, Identify, QueryFeatureCount2, QueryFeatureIds2, QueryFeatureData2 and QueryHyperlinks2.
Although the DefinitionExpression set in the LayerDescription will override any any definition query set in the source map, there are MapServer methods that only honor the expression set in the source document. Any expression set in DefinitionExpression in the LayerDescription will be ignored. These mothods include: QueryFeatureCount, QueryFeatureIds, and QueryFeatureData. MapDescription, which contains the LayerDescriptions, are not a parameter for these methods.
DefinitionExpression does not affect spatial extents.