/// <summary>
/// Constructs a $apply aggregate transformation.
/// E.g. $apply=aggregate(Prop with sum as SumProp, Prop with average as AverageProp)
/// </summary>
/// <param name="aggregations">List of aggregations.</param>
/// <returns>The aggregate tranformation.</returns>
private string ConstructAggregateTransformation(IList <ApplyQueryOptionExpression.Aggregation> aggregations)
{
StringBuilder aggregateBuilder = new StringBuilder();
aggregateBuilder.Append(UriHelper.AGGREGATE);
aggregateBuilder.Append(UriHelper.LEFTPAREN);
int i = 0;
while (true)
{
ApplyQueryOptionExpression.Aggregation aggregation = aggregations[i];
AggregationMethod aggregationMethod = aggregation.AggregationMethod;
string aggregationAlias = aggregation.AggregationAlias;
string aggregationUriEquivalent;
if (!TypeSystem.TryGetUriEquivalent(aggregationMethod, out aggregationUriEquivalent))
{
// This would happen if an aggregation method was added to the enum with no
// relevant update to map it to the URI equivalent
throw new NotSupportedException(Strings.ALinq_AggregationMethodNotSupported(aggregationMethod.ToString()));
}
string aggregationProperty = string.Empty;
// E.g. Amount with sum as SumAmount (For $count aggregation: $count as Count)
if (aggregationMethod != AggregationMethod.VirtualPropertyCount)
{
aggregationProperty = this.ExpressionToString(aggregation.Expression, /*inPath*/ false);
aggregateBuilder.Append(aggregationProperty);
aggregateBuilder.Append(UriHelper.SPACE);
aggregateBuilder.Append(UriHelper.WITH);
aggregateBuilder.Append(UriHelper.SPACE);
}
aggregateBuilder.Append(aggregationUriEquivalent);
aggregateBuilder.Append(UriHelper.SPACE);
aggregateBuilder.Append(UriHelper.AS);
aggregateBuilder.Append(UriHelper.SPACE);
// MUST define an alias for the resulting aggregate value
// Concatenate aggregation method with aggregation property to generate a simple identifier/alias
// OASIS Standard: The alias MUST NOT collide with names of declared properties, custom aggregates, or other aliases in that type
// TODO: Strategy to avoid name collision - Append a Guid?
if (string.IsNullOrEmpty(aggregationAlias))
{
aggregationAlias = aggregationMethod.ToString() + aggregationProperty.Replace('/', '_');
}
aggregateBuilder.Append(aggregationAlias);
if (++i == aggregations.Count)
{
break;
}
aggregateBuilder.Append(UriHelper.COMMA);
}
aggregateBuilder.Append(UriHelper.RIGHTPAREN);
return(aggregateBuilder.ToString());
}