private IEnumerable <IProjectionAttribute> CreateDefaultHeader(IProjectionMetadata metadata)
{
ProjectionIdentity identity = this.Identity;
IProcContext context = this.Context;
IEnumerable <IProjectionMetadata> header = this.SelectAttributes(metadata);
if (this.Data != null)
{
using ProjectionReader reader = new ProjectionReader(this.Data.Source, header);
if (reader.Read())
{
foreach (var(valueMetadata, data) in header.Zip(reader.GetData()))
{
yield return(new ProjectionAttribute(identity, context, valueMetadata, data));
}
yield break;
}
}
foreach (IProjectionMetadata attributeMetadata in header)
{
yield return(new ProjectionAttribute(identity, context, attributeMetadata, data: null));
}
}
public static IEnumerable <IProjectionData> Lookup(IField source, IEnumerable <IProjectionMetadata> header)
{
using ProjectionReader reader = new ProjectionReader(source, header);
if (reader.Read())
{
foreach (IProjectionData data in reader.GetData())
{
yield return(data);
}
}
}
internal static IProjectionData Resolve(IProjectionData data, IProjectionMetadata metadata)
{
if (data == null)
{
return(null);
}
else if (data.Source.Metadata == metadata.Relation)
{
return(data);
}
else
{
return(ProjectionReader.Lookup(data.Source, new[] { metadata }).FirstOrDefault());
}
}