I am using Mongo C# v 2.11.5 to group users by their CategoryId. I would like the variable list_of_groups to contain a list of groups, where each group has a list of all the documents in the group, where each document contains all its individual properties. I don't want to apply any accumulator functions on any fields.
The UserGroup class is:
public class UserGroup
{
public string gid {get; set;}
public List<Users> users { get; set; }
}
My grouping query is
var list_of_groups = UserCollection
.Aggregate()
.Group(usr => usr.CategoryId,
g => new UserGroup { gid = g.Key, users = g.ToList() })
.ToList<UserGroup>();
I would like to create a "list of lists", where each inner list contains all the documents of its grouping i.e. this type of structure:
List<List<UserGroup>>(
- List1<UserGroup> (list of complete documents belonging to CategoryId 1)
- List2<UserGroup> (list of complete documents belonging to CategoryId 2)
- List3<UserGroup> (list of complete documents belonging to CategoryId 3)
)
The doesn't work as the following error is generated at runtime:
System.NotSupportedException
HResult=0x80131515
Message=Specified method is not supported.
Source=MongoDB.Driver
Can anyone point out what I'm missing here? I've been going in circles for a while now. Should I not being using the Group function, and maybe some other function is more appropriate since I don't want to apply any accumulator functions, and because I want each document in each group to have all its properties available?
Stack Trace:
at MongoDB.Driver.Linq.Processors.AccumulatorBinder.GetAccumulatorArgument(Expression node)
at MongoDB.Driver.Linq.Processors.AccumulatorBinder.TryGetAccumulatorTypeAndArgument(PipelineExpression node, AccumulatorType& accumulatorType, Expression& argument)
at MongoDB.Driver.Linq.Processors.AccumulatorBinder.VisitPipeline(PipelineExpression node)
at MongoDB.Driver.Linq.Expressions.PipelineExpression.Accept(ExtensionExpressionVisitor visitor)
at MongoDB.Driver.Linq.Expressions.ExtensionExpression.Accept(ExpressionVisitor visitor)
at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
at MongoDB.Driver.Linq.Processors.AccumulatorBinder.Bind(Expression node, IBindingContext bindingContext)
at MongoDB.Driver.Linq.Processors.EmbeddedPipeline.EmbeddedPipelineBinder.Bind(Expression node, IBindingContext parent)
at MongoDB.Driver.Linq.Processors.SerializationBinder.BindEmbeddedPipeline(MethodCallExpression node)
at MongoDB.Driver.Linq.Processors.SerializationBinder.VisitMethodCall(MethodCallExpression node)
at System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor)
at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
at MongoDB.Driver.Linq.Processors.SerializationBinder.Visit(Expression node)
at System.Linq.Expressions.ExpressionVisitor.VisitMemberAssignment(MemberAssignment node)
at System.Linq.Expressions.ExpressionVisitor.VisitMemberBinding(MemberBinding node)
at System.Linq.Expressions.ExpressionVisitor.Visit[T](ReadOnlyCollection`1 nodes, Func`2 elementVisitor)
at System.Linq.Expressions.ExpressionVisitor.VisitMemberInit(MemberInitExpression node)
at System.Linq.Expressions.MemberInitExpression.Accept(ExpressionVisitor visitor)
at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
at MongoDB.Driver.Linq.Processors.SerializationBinder.Visit(Expression node)
at MongoDB.Driver.Linq.Processors.SerializationBinder.Bind(Expression node, IBindingContext context, Boolean isClientSideProjection)
at MongoDB.Driver.Linq.Processors.PipelineBindingContext.Bind(Expression node, Boolean isClientSideProjection)
at MongoDB.Driver.Linq.Processors.PipelineBindingContext.Bind(Expression node)
at MongoDB.Driver.Linq.Translators.AggregateGroupTranslator.BindGroup[TKey,TDocument,TResult](PipelineBindingContext bindingContext, Expression`1 groupProjector, IBsonSerializer`1 parameterSerializer, Expression keySelector)
at MongoDB.Driver.Linq.Translators.AggregateGroupTranslator.Translate[TKey,TDocument,TResult](Expression`1 idProjector, Expression`1 groupProjector, IBsonSerializer`1 parameterSerializer, IBsonSerializerRegistry serializerRegistry, ExpressionTranslationOptions translationOptions)
at MongoDB.Driver.GroupExpressionProjection`3.Render(IBsonSerializer`1 documentSerializer, IBsonSerializerRegistry serializerRegistry)
at MongoDB.Driver.PipelineStageDefinitionBuilder.<>c__DisplayClass19_0`2.<Group>b__0(IBsonSerializer`1 s, IBsonSerializerRegistry sr)
at MongoDB.Driver.DelegatedPipelineStageDefinition`2.Render(IBsonSerializer`1 inputSerializer, IBsonSerializerRegistry serializerRegistry)
at MongoDB.Driver.AppendedStagePipelineDefinition`3.Render(IBsonSerializer`1 inputSerializer, IBsonSerializerRegistry serializerRegistry)
at MongoDB.Driver.MongoCollectionImpl`1.Aggregate[TResult](IClientSessionHandle session, PipelineDefinition`2 pipeline, AggregateOptions options, CancellationToken cancellationToken)
at MongoDB.Driver.MongoCollectionImpl`1.<>c__DisplayClass19_0`1.<Aggregate>b__0(IClientSessionHandle session)
at MongoDB.Driver.MongoCollectionImpl`1.UsingImplicitSession[TResult](Func`2 func, CancellationToken cancellationToken)
at MongoDB.Driver.MongoCollectionImpl`1.Aggregate[TResult](PipelineDefinition`2 pipeline, AggregateOptions options, CancellationToken cancellationToken)
at MongoDB.Driver.CollectionAggregateFluent`2.ToCursor(CancellationToken cancellationToken)
The problem you're facing here is that everything that's within .Group()
method should get translated into corresponding MongoDB / Aggregation Framework operator and obviously there's no .ToList()
counterpart. Therefore, there's no path forward with LINQ if you want to return a list of documents and you have to use Aggregation Framework's syntax directly and take advantage of $$ROOT variable:
public class UserGroup
{
[BsonElement("_id")]
public string gid { get; set; }
public List<User> users { get; set; }
}
var groupDef = new BsonDocument()
{
{ "_id", "$CategoryId" },
{ "users", new BsonDocument(){ { "$push", "$$ROOT" } } }
};
var res = collection.Aggregate().Group<UserGroup>(groupDef).ToList();
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