Can't convert List<AnonymousType#1> to List<Model>

L A

9y26.3kVisual Basic .NET

Hello all,

In my ASP.NETMVC application have 4 model classes.

ProductModel

public class ProductModel
{
public int ProductID { get; set; }
public string ProductName { get; set; }
public int SupplierID { get; set; }
public int CategoryID { get; set; }
}

CategoriesModel

public class CategoriesModel
{
public int CategoryID { get; set; }
public string CategoryName { get; set; }
public string Description { get; set; }
}

SuppliersModel

public class SuppliersModel
{
public int SupplierID { get; set; }
public string CompanyName { get; set; }
public string ContactName { get; set; }
public string ContactTitle { get; set; }
public string Phone { get; set; }
public string City { get; set; }
public string Country { get; set; }
}

Products_Categories_SuppliersModel - Class with all the required properties from above three classes.

public class Products_Categories_SuppliersModel
{
public string ProductName { get; set; }
public string ContactName { get; set; }
public string ContactTitle { get; set; }
public string CompanyName { get; set; }
public string Phone { get; set; }
public string City { get; set; }
public string Country { get; set; }
public string CategoryName { get; set; }
public string Description { get; set; }
}

I have data in List, List, List. Used LINQ to join all three Lists<>.

public List GetProduct_Category_SupplierData()
{
try
{
List prodData = GetProductsData().ToList();
List categData = GetCategoriesData().ToList();
List supplData = GetSuppliersData();
var DBData = (from p in prodData
join c in categData
on p.CategoryID equals c.CategoryID
join s in supplData on p.SupplierID equals s.SupplierID
select new
{
p.ProductName,
c.CategoryName,
c.Description,
s.ContactName,
s.ContactTitle,
s.CompanyName,
s.Phone,
s.City,
s.Country
});
return DBData.ToList();
}
catch (Exception) { return null; }
finally {}
}

But Line # 24 throws error - Cannot implicitly convert type 'System.Collections.Generic.List' to 'System.Collections.Generic.List'.

What's the mistake in above code.? I have created Products_Categories_SuppliersModel class such that return data should be of 'Products_Categories_SuppliersModel' type.

Please suggest me to figure out my mistakes & help me code in a better way.

Thanks in advance.

5 Replies

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Abhilash J A9y ago
Accepted answer
Just instantiate Products_Categories_SuppliersModel in your select.
var DBData = (from p in prodData
                 join c in categData
                 on p.CategoryID equals c.CategoryID
                 join s in supplData on p.SupplierID equals s.SupplierID
                 select new Products_Categories_SuppliersModel()
                 {
                     p.ProductName,
                     c.CategoryName,
                     c.Description,
                     s.ContactName,
                     s.ContactTitle,
                     s.CompanyName,
                     s.Phone,
                     s.City,
                     s.Country
                 });
Or

Write your select statement like this
select new  MVCApp.Models.Products_Categories_SuppliersModel
{
ProductName = p.ProductName,
CategoryName = c.CategoryName,
Description = c.Description,
ContactName = s.ContactName,
ContactTitle = s.ContactTitle,
CompanyName = s.CompanyName,
Phone = s.Phone,
City = s.City,
Country = s.Country };
+3
L A9y ago
Thanks Mobeen Rashid, Mani Kandan for your reply. Mobeen Rashid, i already had Products_Categories_SuppliersModel class with all properties i needed in my application.

Thnaks again to everyone, for your suggestions/ comments.
0
Mobeen Rashid9y ago
First thing first, the problem is in your return type not in query or in .ToList(). In LINQ query you are taking data from different model types and projecting it out into a new anonymous type at here
select new  {
                         p.ProductName,
                         c.CategoryName,
                         c.Description,
                         s.ContactName,
                         s.ContactTitle,
                         s.CompanyName,
                         s.Phone,
                         s.City,
                         s.Country
                     }
LINQ query will return data in IQueryable and next line you are converting it to a List object like this List but your method's return type is List, So runtime will throw a casting exception here.
Solution to this problem is that you create a Dto class that contains all the properties that you want to return
public class SampleDto{
     public string ProductName;
     public string CategoryName;
     public string Description;
     public string ContactName;
     public string ContactTitle;
     public string CompanyName;
     public string Phone;
     public string City;
     public string Country;
}
And now you return Dto Instean of creating an anonymous object.
var DBData = (from p in prodData
                     join c in categData
                     on p.CategoryID equals c.CategoryID
                     join s in supplData on p.SupplierID equals s.SupplierID
                     select new SampleDto
                     {
                          ProductName=p.ProductName,
                         CategoryName=c.CategoryName,
                         Description=c.Description,
                         ContactName=s.ContactName,
                         ContactTitle=s.ContactTitle,
                         CompanyName=s.CompanyName,
                         Phone=s.Phone,
                         City=s.City,
                         Country=s.Country
                     });
And change the return type of your method to List
public List GetProduct_Category_SupplierData()
{
    try
    {
+1
L A9y ago
Thanks, Rajkiran Swain, for your reply. I did go thru link you shared, which says to return not just ProductName but the product itself. But im trying to return columns from differnt List's. And i already created class of type 'Products_Categories_SuppliersModel'.

Please correct me if im wrong. And suggest what changes to be made in my code to achieve this.
0
Rajkiran Swain9y ago
https://stackoverflow.com/questions/30392222/cannot-implicitly-convert-type-system-collections-generic-liststring-to-sys
0