C＃聚合来自多个列的数据，这些列来自使用Entity Framework6的RAW SQL查询的结果集中，并将这些数据添加到ViewModel中的列表中

Question

I want to process the data from my database-query using raw SQL in Entity Framework 6 as follows and need a best practice by the use of native functions of C# and LINQ:

PICTURE 1: Resultset taken from database

I have created a class for the resultset above, it looks like that:

public class ProjectQueryModel {

        public int Project { get; set; }
        public string Projectname { get; set; }

        public int RoomId { get; set; }
        public string RoomName { get; set; }

        public int? EmployeeId { get; set; }
        public string EmployeeName { get; set; }

        public int? QualificationId { get; set; }
        public string QualificationName { get; set; }
        public int? QualificationLevel { get; set; }
}

To this point the query works and I got all my data from it stored in a List of type ProjectQueryModel . Now I want to add this data to my ViewModel and don't know how to use the functions C# offers me to process the data of resultsets. How can I achieve the following by saving every entity of type ProjectViewModel in a List, whose objects have the following structure:

PICTURE 2: data organisation in ViewModel

An example dataset for project 1 in the target list should look like this:

ProjectId = 1
Projectname =   T1
RoomId =    1
RoomName =  Delta Room
======================
Employees *(Attribute of type List <ProjectEmployeesVM> )*
  [0].EmployeeId = 2
  [0].EmployeeName = Mee
  [0].EmployeeQualifications *(Attribute of type List<EmployeeQualificationsVM)*
      [0].EmployeeQualifications[0].QualificationId = 1
      [0].EmployeeQualifications[0].QualificationName = Programmer
      [0].EmployeeQualifications[0].QualificationLevel = 3
      ...any other qualification of the employee
  [1].EmployeeId = 2
  [1].EmployeeName = Mee
  [1].EmployeeQualifications
      [1].EmployeeQualifications[0]
  ...Any other employee in this project and all of his qualifications

What I also want to achieve is to save a empty list in case the project has no employees , because the resultset is achieved by the use of LEFT OUTER JOINS. For the qualifications it is not necessary, because every employee has at least one qualification.

VERY BIG THANKS in advance

Answer 1

I'm supposing you have a constructor in every class involved that takes all the properties as arguments.

Here's how i would do it:

List<ProjectQueryModel> queryResult = ...;

List<ProyectViewModel> views = queryResult
    // Take all the rows that belong to one proyect
    .GroupBy(m => m.Proyect)
    // Convert every group into a ProyectViewModel
    // First use Select to Map every Group into a new Proyect using a function that takes a group of rows and return a Proyect
    // Then we use Aggregate inside that mapping function to collapse the entire group of rows into a single ProyectViewModel
    // We'll need a contructor in ProyectViewModel that gives us a completly empty instance
    // Aggregate takes a starting point, and a function that takes that starting point, and passes it every element of the IEnumerable we're using. The return value of that function is the "new starting point".
    // Using this we'll build the Proyect from every row.
    .Select(g => g.Aggregate(new ProyectViewModel(), (pvm, nxtRow) => {
        // Check if we haven't initialized the instance, and do so.
        if (pvm.ProyectId == null) pvm.ProyectId = nxtRow.Proyect;
        if (pvm.ProyectName == null) pvm.ProyectName = nxtRow.ProyectName;
        if (pvm.RoomId == null) pvm.RoomId = nxtRow.RoomId;
        if (pvm.RoomName == null) pvm.RoomName = nxtRow.RoomName;
        if (pvm.Employees == null) pvm.Employees = new List<ProyectEmployeeViewModel>();

        // If the row has an employee
        if (nxtRow.EmployeeId.HasValue) {
            // If the Employee is not yet on the Proyect add it
            if (!pvm.Employees.Any(e => e.EmployeeId == nxtRow.EmployeeId))                                
            {
                // This constructor should create the empty List of Qualifications
                pvm.Employees.Add(new ProyectEmployeeViewModel(nxtRow.EmployeeId.Value, nxtRow.EmployeeName);
            }

            // If the row has a qualification
            if (nxtRow.QualificationId.HasValue)
            {
                // Find it's employee
                pvm.Employees.First(e => e.EmployeeId == nxtRow.EmployeeId)
                // Add the current row's qualification to the employee
                    .Qualifications.Add(new EmployeeQualificationsViewModel(nxtRow.QualificationId.Value, nxtRow.QualificationName, nxtRow.QualificationLevel.Value));
            }
        }

        // Return the Proyect with the changes we've made so we keep building it
        return pvm;
    })).ToList();

LINQ is quite a beauty isn't it?

There might be errors, but use this as a starting point.

Answer 2

Start by making sure that your database has the right foreign key constraints between your tables, then update your model. This will automatically create the correct navigation properties. I've assumed they will be called Employees and Qualifications, but change as appropriate.

Then your query just becomes:

var result=db.Projects
  .Include(p=>p.Employees)
  .Include(p=>p.Employees.Select(e=>e.Qualifications))
  .Where(p=>p.id==1)
  .AsEnumerable(); // or .ToList() if you prefer

Then just pass IEnumerable<Project> to your view (or just Project if your view will always only get 1 Project -- in that case, just end the query with .First() instead of .AsEnumerable() ) . Unless of course you like creating ViewModels, but I'm guessing you don't and this isn't a project that needs the added complexity or abstractions.

The above code assumes you have the following tables:

Project (int Id, varchar(50) Name, int RoomId)
Room (int Id, int Name)
Employee (int Id, varchar(50) Name)
Qualification (int Id,varchar(50) Name, int Level)

Cross Reference tables:

ProjectEmployees (int ProjectId, int EmployeeId)
EmployeeQualifications (int EmployeeId, int QualificationId)

Foreign Keys:

Project.RoomId -> Room.Id
ProjectEmployees.ProjectId -> Project.Id
ProjectEmployees.EmployeeId -> Employee.Id
EmployeeQualifications.EmployeeId -> Employee.Id
EmployeeQualifications.QualificationId -> Qualification.Id