Developer's Guide - MapGuide Open Source - OSGeo

Querying Feature Data
In order to work with feature data, you must first select the features you are
interested in. This can be done with the Viewer or through Web API calls.
Feature Readers
A feature reader, represented by an MgFeatureReader object, is used to iterate
through a list of features. Typically, the feature reader is created by selecting
features from a feature source.
To create a feature reader, use the MgFeatureService::SelectFeatures()
method. See Selecting with the Web API (page 35) for details about selection.
To process the features in a feature reader, use the
MgFeatureReader::ReadNext() method. You must call this method before
being able to read the first feature. Continue calling the method to process
the rest of the features.
The MgFeatureReader::GetPropertyCount() method returns the number of
properties available for the current feature. When you know the name and
type of the feature property, call one of the
MgFeatureReader::GetPropertyType() methods (where PropertyType
represents one of the available types) to retrieve the value. Otherwise, call
MgFeatureReader::GetPropertyName() and
MgFeatureReader::GetPropertyType() before retrieving the value.
Selecting with the Web API
Selections can be created programatically with the Web API. This is done by
querying data in a feature source, creating a feature reader that contains the
features, then converting the feature reader to a selection (MgSelection object).
To create a feature reader, apply a selection filter to a feature class in the feature
source. A selection filter can be a basic filter, a spatial filter, or a combination
of the two. The filter is stored in an MgFeatureQueryOptions object.
Basic filters are used to select features based on the values of feature properties.
For example, you could use a basic filter to select all roads that have four or
more lanes.
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