I have two collections, one is a list of image names, the second is a subset of that list. When a task has been completed its name is inserted into the second collection.
I need to retrieve a set of not yet completed image names from the first collection. I have achieved this successfully with:
var processedNames = processed.AsQueryable().Select(x => x.ImageName).ToArray();
foreach (var result in results.Where(x => !processedNames.Contains(x.ImageName))
However this brings a large list of strings back from the database and then sends it back to the database in a single document, which as well as being inefficient will break eventually.
So I tried to rewrite it so it's all performed server side with:
var results = from x in captures
join complete in processed.AsQueryable() on x.ImageName equals complete.ImageName into completed
where !completed.Any()
select x;
This fails with:
System.NotSupportedException: '$project or $group does not support {document}.'
I also tried using the non LINQ API:
var xs = capturesCollection.Aggregate()
.Lookup("Processed", "ImageName", "ImageName", @as: "CompletedCaptures")
.Match(x => x["CompletedCaptures"] == null)
.ToList();
This fails with:
MongoDB.Bson.BsonSerializationException: 'C# null values of type 'BsonValue' cannot be serialized using a serializer of type 'BsonValueSerializer'.'
How can I achieve this query completely server side with the C# driver? A pure LINQ solution is preferable for portability.
I worked out how to do it with the Aggregate API:
var results = capturesCollection.Aggregate()
.As<CaptureWithCompletions>()
.Lookup(processed, x => x.ImageName, x => x.ImageName, @as:(CaptureWithCompletions x) => x.CompletedCaptures)
.Match(x => !x.CompletedCaptures.Any())
//.Limit(2)
.ToList();