Aggregating Lists inside of a List of objects using LINQ

Question

As a follow up to this question , where I needed to aggregate over inner arrays in MongoDB, I am trying to accomplish the same task in LINQ.

I am close, as I have figured out how to aggregate over an individual item:

// 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();

However, I can't use ...First() on the collection, because there might be multiple VehicleDataUploads for a project. How can I aggregate over all the lists inside the list of documents that are returned?

Answer 1

Try something as follows:

// 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();