Question

任何人都可以帮助我理解为什么我得到以下消息：“ System.NullReferenceException：'对象引用未设置为对象的实例。在方法的最后一行。我的目标是在要查询的同一集合中建立自我查找。我认为这与驱动程序无法正确序列化模型有关，但是我无法理解为什么会发生这种情况。

public void CanGetAggregatedComponents()
    {

        PipelineStageDefinition<ComponentRecordDataModel, AggregatedAlignedComponentRecordDataModel> lookup;

        lookup = PipelineStageDefinitionBuilder.Lookup<ComponentRecordDataModel,
            ComponentRecordDataModel,
            AggregatedAlignedComponentRecordDataModel>(
            _mongoContext.Collection,
            local => local.RecordAlignments,
            foreign => foreign.Id,
            (AggregatedAlignedComponentRecordDataModel lookupResult) =>lookupResult
        );

      //  var expectedLookup =
        //    @"{$lookup: { from: 'componentRecord', localField: 'recordAlignments', foreignField: '_id', as: 'alignedToRecord' } }";

        var rendered = lookup.Render(BsonSerializer.SerializerRegistry.GetSerializer<ComponentRecordDataModel>(),
           BsonSerializer.SerializerRegistry);

    }

Answer 1

您的查询可能为空。试试这个：

public void CanGetAggregatedComponents()
    {

        PipelineStageDefinition<ComponentRecordDataModel, AggregatedAlignedComponentRecordDataModel> lookup;

        lookup = PipelineStageDefinitionBuilder.Lookup<ComponentRecordDataModel,
            ComponentRecordDataModel,
            AggregatedAlignedComponentRecordDataModel>(
            _mongoContext.Collection,
            local => local.RecordAlignments,
            foreign => foreign.Id,
            (AggregatedAlignedComponentRecordDataModel lookupResult) =>lookupResult
        );

      //  var expectedLookup =
        //    @"{$lookup: { from: 'componentRecord', localField: 'recordAlignments', foreignField: '_id', as: 'alignedToRecord' } }";
   if(lookup !=null)
   {
        var rendered = lookup.Render(BsonSerializer.SerializerRegistry.GetSerializer<ComponentRecordDataModel     >(),BsonSerializer.SerializerRegistry);
   }
}

或这个

public void CanGetAggregatedComponents()
    {

        PipelineStageDefinition<ComponentRecordDataModel, AggregatedAlignedComponentRecordDataModel> lookup;

        lookup = PipelineStageDefinitionBuilder.Lookup<ComponentRecordDataModel,
            ComponentRecordDataModel,
            AggregatedAlignedComponentRecordDataModel>(
            _mongoContext.Collection,
            local => local.RecordAlignments,
            foreign => foreign.Id,
            (AggregatedAlignedComponentRecordDataModel lookupResult) =>lookupResult
        );

      //  var expectedLookup =
        //    @"{$lookup: { from: 'componentRecord', localField: 'recordAlignments', foreignField: '_id', as: 'alignedToRecord' } }";

        var rendered = lookup?.Render(BsonSerializer.SerializerRegistry.GetSerializer<ComponentRecordDataModel>(),
           BsonSerializer.SerializerRegistry);

    }

C＃驱动程序Mongo $ lookup修复

1 个答案: