使用LINQ在对象列表内部聚合列表

Question

作为后续到this question，我需要在MongoDB中聚合内部数组，我试图在LINQ中完成相同的任务。

我靠近，我已经找到了如何聚合在一个单独的项目：

// Get collection 
var collection = _database.GetCollection<VehicleDataUpload>("Vehicles"); 

// Get first project that meets our identifier 
var firstProject = collection.AsQueryable().Where(i => i.ProjectId.Equals("1234")).First(); 

// Get a list of DailySummaryData objects 
var aggregation = 
    from entry in firstProject.VehicleEntries 
    group entry by entry.Data 
    into result 
    select new DailySummaryData() { 
     ProjectName = firstProject.ProjectId, 
     Date = result.FirstOrDefault().Date, 
     Passed = result.Sum(x => (x.VehicleStatus.Equals("PASSED") ? 1 : 0)), 
     Failed = result.Sum(x => (x.VehicleStatus.Equals("FAILED") ? 1 : 0)) 
    }; 

return aggregation.ToList(); 

但是，我不能收集使用...First()，因为有可能是一个项目中多个VehicleDataUploads。如何汇总返回的文档列表中的所有列表？

Answer 1

试试如下：

// Get collection 
var collection = _database.GetCollection<VehicleDataUpload>("Vehicles"); 

// Get first project that meets our identifier 
var aggregation = collection 
    .AsQueryable() 
    // This will return an IEnumerable of Vehicles object 
    .Where(i => i.ProjectId.Equals("1234")) 
    // Assuming you want to return a plain list, you should use SelectMany 
    .SelectMany(v => v.VehicleEntries 
     // You group each list of VehicleEntries 
     .GroupBy(ve => ve.Data) 
     // For each group you return a new DailySummaryData object 
     .Select(g => new DailySummaryData() { 
      ProjectName = v.ProjectId, 
      Date = g.Key, 
      Passed = g.Sum(x => (x.VehicleStatus.Equals("PASSED") ? 1 : 0)), 
      Failed = g.Sum(x => (x.VehicleStatus.Equals("FAILED") ? 1 : 0)) 
     }) 

return aggregation.ToList();