Unknown Typically you would use this with a polymorphic collection, but it fails the same way when querying for the collection's type.
using System; using MongoDB.Bson; using MongoDB.Driver; using MongoDB.Driver.Linq; var client = new MongoClient(); var db = client.GetDatabase("test"); var coll = db.GetCollection<Animal>("zoo"); var query = coll.AsQueryable().Where(e => e.GetType() == typeof(Animal)); Console.WriteLine(query); record Animal(ObjectId Id);
Stack trace:
System.NullReferenceException: Object reference not set to an instance of an object. at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToFilterTranslators.ExpressionTranslators.GetTypeComparisonExpressionToFilterTranslator.Translate(TranslationContext context, BinaryExpression expression, MethodCallExpression getTypeExpression, Expression typeConstantExpression) in /Users/james/Dropbox/code/mongodb/mongo-csharp-driver/src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToFilterTranslators/ExpressionTranslators/GetTypeComparisonExpressionToFilterTranslator.cs:line 51 at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToFilterTranslators.ExpressionTranslators.ComparisonExpressionToFilterTranslator.Translate(TranslationContext context, BinaryExpression expression) in /Users/james/Dropbox/code/mongodb/mongo-csharp-driver/src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToFilterTranslators/ExpressionTranslators/ComparisonExpressionToFilterTranslator.cs:line 61 at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToFilterTranslators.ExpressionToFilterTranslator.TranslateUsingQueryOperators(TranslationContext context, Expression expression) in /Users/james/Dropbox/code/mongodb/mongo-csharp-driver/src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToFilterTranslators/ExpressionToFilterTranslator.cs:line 97 at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToFilterTranslators.ExpressionToFilterTranslator.Translate(TranslationContext context, Expression expression, Boolean exprOk) in /Users/james/Dropbox/code/mongodb/mongo-csharp-driver/src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToFilterTranslators/ExpressionToFilterTranslator.cs:line 37 at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToFilterTranslators.ExpressionToFilterTranslator.TranslateLambda(TranslationContext context, LambdaExpression lambdaExpression, IBsonSerializer parameterSerializer, Boolean asRoot) in /Users/james/Dropbox/code/mongodb/mongo-csharp-driver/src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToFilterTranslators/ExpressionToFilterTranslator.cs:line 70 at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.WhereMethodToPipelineTranslator.Translate(TranslationContext context, MethodCallExpression expression) in /Users/james/Dropbox/code/mongodb/mongo-csharp-driver/src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToPipelineTranslators/WhereMethodToPipelineTranslator.cs:line 39 at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.ExpressionToPipelineTranslator.Translate(TranslationContext context, Expression expression) in /Users/james/Dropbox/code/mongodb/mongo-csharp-driver/src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToPipelineTranslators/ExpressionToPipelineTranslator.cs:line 73 at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToExecutableQueryTranslators.ExpressionToExecutableQueryTranslator.Translate[TDocument,TOutput](MongoQueryProvider`1 provider, Expression expression) in /Users/james/Dropbox/code/mongodb/mongo-csharp-driver/src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToExecutableQueryTranslators/ExpressionToExecutableQueryTranslator.cs:line 32 at MongoDB.Driver.Linq.Linq3Implementation.MongoQuery`2.ToString() in /Users/james/Dropbox/code/mongodb/mongo-csharp-driver/src/MongoDB.Driver/Linq/Linq3Implementation/MongoQuery.cs:line 109
The root cause is in GetTypeComparisonExpressionToFilterTranslator line 49. If the nominalType matches the actualType and the hierarchy wasn't configured with a RootClass (e.g. [BsonDiscriminator(RootClass = true)]), then GetDiscriminator returns null and we throw on line 51 discrminatorValue.IsBsonArray).