/// <summary>
/// Downloads records and yields them as a lazy sequence of features of the specified type. Possibly throws RestException.
/// </summary>
/// <typeparam name="T">The type the record should be mapped to.</typeparam>
/// <param name="layerId">The layer ID of the feature layer or table.</param>
/// <param name="whereClause">The where clause. If set to null, returns all features.</param>
/// <param name="extraParameters">The query string that describes any additional query parameters (i.e. outSR=4326). Each parameter must be url encoded.</param>
/// <param name="keepQuerying">If set to true, repetitively queries the server until all features have been returned.</param>
/// <param name="degreeOfParallelism">The maximum number of concurrent requests.</param>
/// <returns></returns>
public IEnumerable <T> Download <T>(int layerId, string whereClause = null, string extraParameters = null, bool keepQuerying = false, int degreeOfParallelism = 1) where T : Feature
{
var layer = GetLayer(layerId);
var returnGeometry = typeof(T).HasGeometry();
var featureSet = Esri.GetFeatureSet(ServiceArgs, layerId, returnGeometry, layer.hasZ, whereClause, extraParameters, null);
foreach (var g in featureSet.features)
{
yield return(ToFeature <T>(g, layer));
}
var objectIds = featureSet.features.Select(g => Convert.ToInt32(g.attributes[layer.GetObjectIdFieldName()])).ToArray();
if (!keepQuerying || objectIds.Length == 0)
{
yield break;
}
var remainingObjectIds = Esri.GetOIDSet(ServiceArgs, layerId, whereClause, extraParameters).objectIds.Except(objectIds);
foreach (var f in Download <T>(layer, remainingObjectIds, returnGeometry, whereClause, extraParameters, objectIds.Length, degreeOfParallelism))
{
yield return(f);
}
}
private IEnumerable <T> Download <T>(Layer layer, IEnumerable <int> objectIds, bool returnGeometry, string whereClause, string extraParameters, int batchSize, int degreeOfParallelism) where T : Feature
{
return(objectIds.Partition(batchSize)
.AsParallel()
.AsOrdered()
.WithDegreeOfParallelism(degreeOfParallelism < 1 ? 1 : degreeOfParallelism)
.SelectMany(ids => Esri.GetFeatureSet(ServiceArgs, layer.id, returnGeometry, layer.hasZ, whereClause, extraParameters, ids).features
.Select(g => ToFeature <T>(g, layer))));
}
