从列表创建嵌套模型

Question

I have an existing class

    public class Employee
{
    public int? EmployeeId { get; set; }
    public string EmployeeName { get; set; }
    public int? LocationId { get; set; }
    public string LocationName { get; set; }
    public int? DesignationId { get; set; }
    public string DesignationName { get; set; }
}

Code for fetching data from database:

using (var ds = new EmployeeDS())
                {
                    using (var dataAdapter = new DataSet.EmployeeDSTableAdapters.EmployeeTableAdapter())
                    {
                    dataAdapter.FillEmployee(ds.Employee,Id);
                      var result = (from DataRow row in ds.Employee.Rows
                                  select new Employee
                                  {
                                      EmployeeId = (row["EmployeeID"] == DBNull.Value) ? null : (int?)row["EmployeeID"],
                                      EmployeeName = (row["EmployeeName"] == DBNull.Value) ? string.Empty : (string)row["EmployeeName"],
                                      LocationId = (row["LocationId"] == DBNull.Value) ? null : (int?)row["LocationId"],
                                      LocationName = (row["LocationName"] == DBNull.Value) ? string.Empty : (string)row["LocationName"],
                                      DesignationId = (row["DesignationId"] == DBNull.Value) ? null : (int?)row["DesignationId"],
                                      DesignationName = (row["DesignationName"] == DBNull.Value) ? string.Empty : (string)row["DesignationName"],
                                  }).ToList();
                    }
                }

Its working fine.But this returning multiple rows for a employee having multiple location or designation.So I need to return the data as nested model like :

public class EmployeeNested
    {
        public int? EmployeeId { get; set; }
        public string EmployeeName { get; set; }
        public List<Location> Locations { get; set; }
        public List<Designation> Designations { get; set; }
    }
    public class Location
    {
        public int? LocationId { get; set; }
        public string LocationName { get; set; }
    }
    public class Designation
    {   
     public int? DesignationId { get; set; }
     public string DesignationName { get; set; }
    }

I am using this code for returning nested model:

 var tempList=result.GroupBy(x => x.EmployeeId, (key, g) => g.OrderBy(e => e.EmployeeId).First());
                    foreach (var item in tempList)
                    {
                        item.Designations = result
                                          .Where(x => x.EmployeeId== item.EmployeeId)
                                          .Select(x => new Designation
                                                 {
                                                  DesignationId = x.DesignationId,
                                                  DesignationName = x.DesignationName
                                                 }).ToList();
                        item.Locations = result
                                          .Where(x => x.EmployeeId== item.EmployeeId)
                                          .Select(x => new Location
                                                 {
                                                  LocationId = x.LocationId,
                                                  LocationName = x.LocationName
                                                 }).ToList();
                    }

Question:

• Is there any better solution to convert a flat list to nested List?.

• Is it possible to create a generic method for converting flat list to nested list?. So that I can reuse it for another functions too.

• Is it possible to create a nested list directly from dataset?

I'm sure there is a good solid pattern for doing this, I just can't find it.

Answer 1

I don't think there is a way to create a nested list from a dataset other than looping through the results and some programming logic. If your using a relational database I would recommend using entity framework which would generate something similar to your EmployeeNested class once you have your database properly configured.

Answer 2

Is there any better solution to convert a flat list to nested List?.

As per my knowledge better solution is to create utility methods which take input list and processed it into another type of list. Please refer below sample code.

public static List<EmployeeNested> ProcessEmployeeData(List<Employee> result)
        {
            return result.Where(x => x.EmployeeId.HasValue).GroupBy(x => x.EmployeeId.Value).Select(x => new EmployeeNested
            {
                EmployeeId = x.Key,
                EmployeeName = x.First().EmployeeName,
                Locations = x.Select(s => new Location
                {
                    LocationId = s.LocationId,
                    LocationName = s.LocationName
                }).ToList(),
                Designations = x.Select(s => new Designation
                {
                    DesignationId = s.DesignationId,
                    DesignationName = s.DesignationName
                }).ToList()
            }).ToList();
        }

Is it possible to create a generic method for converting flat list to nested list?. So that I can reuse it for another functions too.

We can't make generic methods unless if there is common property which inherits all property, and how that generic method knows that in which collection need to add some specific object. If there is the way then it going to be complex to implement.

Is it possible to create a nested list directly from dataset?

As per my understanding, we can't make nested collection directly from a dataset, because dataset has no knowledge about in which type of collection we want to bind data which is fetched from the database. if you want to make direct collection then there must be an underlying structure which query database according to our model and bind, that is how ORM framework works like entity framework.