OGR
Public Member Functions

OGRGenSQLResultsLayer Class Reference

Inheritance diagram for OGRGenSQLResultsLayer:
OGRLayer

List of all members.

Public Member Functions

virtual OGRGeometryGetSpatialFilter ()
virtual void ResetReading ()
virtual OGRFeatureGetNextFeature ()
virtual OGRErr SetNextByIndex (long nIndex)
virtual OGRFeatureGetFeature (long nFID)
virtual OGRFeatureDefnGetLayerDefn ()
virtual OGRSpatialReferenceGetSpatialRef ()
virtual int GetFeatureCount (int bForce=TRUE)
virtual OGRErr GetExtent (OGREnvelope *psExtent, int bForce=TRUE)
virtual int TestCapability (const char *)

Member Function Documentation

OGRErr OGRGenSQLResultsLayer::GetExtent ( OGREnvelope psExtent,
int  bForce = TRUE 
) [virtual]

Fetch the extent of this layer.

Returns the extent (MBR) of the data in the layer. If bForce is FALSE, and it would be expensive to establish the extent then OGRERR_FAILURE will be returned indicating that the extent isn't know. If bForce is TRUE then some implementations will actually scan the entire layer once to compute the MBR of all the features in the layer.

Depending on the drivers, the returned extent may or may not take the spatial filter into account. So it is safer to call GetExtent() without setting a spatial filter.

Layers without any geometry may return OGRERR_FAILURE just indicating that no meaningful extents could be collected.

This method is the same as the C function OGR_L_GetExtent().

Parameters:
psExtentthe structure in which the extent value will be returned.
bForceFlag indicating whether the extent should be computed even if it is expensive.
Returns:
OGRERR_NONE on success, OGRERR_FAILURE if extent not known.

Reimplemented from OGRLayer.

References OGRLayer::GetExtent().

OGRFeature * OGRGenSQLResultsLayer::GetFeature ( long  nFID) [virtual]

Fetch a feature by it's identifier.

This function will attempt to read the identified feature. The nFID value cannot be OGRNullFID. Success or failure of this operation is unaffected by the spatial or attribute filters.

If this method returns a non-NULL feature, it is guaranteed that it's feature id (OGRFeature::GetFID()) will be the same as nFID.

Use OGRLayer::TestCapability(OLCRandomRead) to establish if this layer supports efficient random access reading via GetFeature(); however, the call should always work if the feature exists as a fallback implementation just scans all the features in the layer looking for the desired feature.

Sequential reads are generally considered interrupted by a GetFeature() call.

This method is the same as the C function OGR_L_GetFeature().

Parameters:
nFIDthe feature id of the feature to read.
Returns:
a feature now owned by the caller, or NULL on failure.

Reimplemented from OGRLayer.

References OGRFeature::Clone(), OGRLayer::GetFeature(), OGRFeature::SetFID(), and OGRFeature::SetField().

Referenced by GetNextFeature().

int OGRGenSQLResultsLayer::GetFeatureCount ( int  bForce = TRUE) [virtual]

Fetch the feature count in this layer.

Returns the number of features in the layer. For dynamic databases the count may not be exact. If bForce is FALSE, and it would be expensive to establish the feature count a value of -1 may be returned indicating that the count isn't know. If bForce is TRUE some implementations will actually scan the entire layer once to count objects.

The returned count takes the spatial filter into account.

This method is the same as the C function OGR_L_GetFeatureCount().

Parameters:
bForceFlag indicating whether the count should be computed even if it is expensive.
Returns:
feature count, -1 if count not known.

Reimplemented from OGRLayer.

References OGRLayer::GetFeatureCount().

OGRFeatureDefn * OGRGenSQLResultsLayer::GetLayerDefn ( ) [virtual]

Fetch the schema information for this layer.

The returned OGRFeatureDefn is owned by the OGRLayer, and should not be modified or freed by the application. It encapsulates the attribute schema of the features of the layer.

This method is the same as the C function OGR_L_GetLayerDefn().

Returns:
feature definition.

Implements OGRLayer.

OGRFeature * OGRGenSQLResultsLayer::GetNextFeature ( ) [virtual]

Fetch the next available feature from this layer. The returned feature becomes the responsiblity of the caller to delete.

Only features matching the current spatial filter (set with SetSpatialFilter()) will be returned.

This method implements sequential access to the features of a layer. The ResetReading() method can be used to start at the beginning again.

This method is the same as the C function OGR_L_GetNextFeature().

Returns:
a feature, or NULL if no more features are available.

Implements OGRLayer.

References GetFeature(), and OGRLayer::GetNextFeature().

OGRGeometry * OGRGenSQLResultsLayer::GetSpatialFilter ( ) [virtual]

This method returns the current spatial filter for this layer.

The returned pointer is to an internally owned object, and should not be altered or deleted by the caller.

This method is the same as the C function OGR_L_GetSpatialFilter().

Returns:
spatial filter geometry.

Reimplemented from OGRLayer.

OGRSpatialReference * OGRGenSQLResultsLayer::GetSpatialRef ( ) [virtual]

Fetch the spatial reference system for this layer.

The returned object is owned by the OGRLayer and should not be modified or freed by the application.

This method is the same as the C function OGR_L_GetSpatialRef().

Returns:
spatial reference, or NULL if there isn't one.

Reimplemented from OGRLayer.

References OGRLayer::GetSpatialRef().

void OGRGenSQLResultsLayer::ResetReading ( ) [virtual]

Reset feature reading to start on the first feature. This affects GetNextFeature().

This method is the same as the C function OGR_L_ResetReading().

Implements OGRLayer.

References OGRLayer::ResetReading(), OGRLayer::SetAttributeFilter(), and OGRLayer::SetSpatialFilter().

OGRErr OGRGenSQLResultsLayer::SetNextByIndex ( long  nIndex) [virtual]

Move read cursor to the nIndex'th feature in the current resultset.

This method allows positioning of a layer such that the GetNextFeature() call will read the requested feature, where nIndex is an absolute index into the current result set. So, setting it to 3 would mean the next feature read with GetNextFeature() would have been the 4th feature to have been read if sequential reading took place from the beginning of the layer, including accounting for spatial and attribute filters.

Only in rare circumstances is SetNextByIndex() efficiently implemented. In all other cases the default implementation which calls ResetReading() and then calls GetNextFeature() nIndex times is used. To determine if fast seeking is available on the current layer use the TestCapability() method with a value of OLCFastSetNextByIndex.

This method is the same as the C function OGR_L_SetNextByIndex().

Parameters:
nIndexthe index indicating how many steps into the result set to seek.
Returns:
OGRERR_NONE on success or an error code.

Reimplemented from OGRLayer.

References OGRLayer::SetNextByIndex().

int OGRGenSQLResultsLayer::TestCapability ( const char *  pszCap) [virtual]

Test if this layer supported the named capability.

The capability codes that can be tested are represented as strings, but #defined constants exists to ensure correct spelling. Specific layer types may implement class specific capabilities, but this can't generally be discovered by the caller.

  • OLCRandomRead / "RandomRead": TRUE if the GetFeature() method is implemented in an optimized way for this layer, as opposed to the default implementation using ResetReading() and GetNextFeature() to find the requested feature id.

  • OLCSequentialWrite / "SequentialWrite": TRUE if the CreateFeature() method works for this layer. Note this means that this particular layer is writable. The same OGRLayer class may returned FALSE for other layer instances that are effectively read-only.

  • OLCRandomWrite / "RandomWrite": TRUE if the SetFeature() method is operational on this layer. Note this means that this particular layer is writable. The same OGRLayer class may returned FALSE for other layer instances that are effectively read-only.

  • OLCFastSpatialFilter / "FastSpatialFilter": TRUE if this layer implements spatial filtering efficiently. Layers that effectively read all features, and test them with the OGRFeature intersection methods should return FALSE. This can be used as a clue by the application whether it should build and maintain it's own spatial index for features in this layer.

  • OLCFastFeatureCount / "FastFeatureCount": TRUE if this layer can return a feature count (via OGRLayer::GetFeatureCount()) efficiently ... ie. without counting the features. In some cases this will return TRUE until a spatial filter is installed after which it will return FALSE.

  • OLCFastGetExtent / "FastGetExtent": TRUE if this layer can return its data extent (via OGRLayer::GetExtent()) efficiently ... ie. without scanning all the features. In some cases this will return TRUE until a spatial filter is installed after which it will return FALSE.

  • OLCFastSetNextByIndex / "FastSetNextByIndex": TRUE if this layer can perform the SetNextByIndex() call efficiently, otherwise FALSE.

This method is the same as the C function OGR_L_TestCapability().

Parameters:
pszCapthe name of the capability to test.
Returns:
TRUE if the layer has the requested capability, or FALSE otherwise. OGRLayers will return FALSE for any unrecognised capabilities.

Implements OGRLayer.

References OGRLayer::TestCapability().


The documentation for this class was generated from the following files:

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