C# 实体框架 Inheritance：自动将属性映射到子属性

Question

I was wondering if we can automatically map a property into children property when retrieving from database.

Example:

public class Account
{
    [Key]
    [Index(IsUnique = true)]
    public Guid ID { get; set; } = Guid.NewGuid();

    [Required]
    [Index(IsUnique = true)]
    [StringLength(50)]
    public string Email { get; set; }

    [Required]
    public string Password { get; set; }

    public string Hash { get; set; }

    public ICollection<Role> Roles { get; set; }

    [ForeignKey("AccountProfile")]
    public Guid? AccountProfileId { get; set; }

    public virtual AccountProfile AccountProfile { get; set; }
}

public class AccountProfile
{
    [Key]
    [Index(IsUnique = true)]
    public Guid ID { get; set; } = Guid.NewGuid();

    [Required]
    public string Name { get; set; }

    [Required]
    public string Phone { get; set; }

    public ICollection<AccountAddress> Addresses { get; set; }
}

And then I make a view model:

[NotMapped]
public class AccountVM : Account
{
    public string Name { get; set; } //Map this into AccountProfile.Name
}

I want to auto map the Name into base.AccountProfile.Name when retrieving the data from database:

List<AccountVM> models = db.Accounts.Include(m => m.Roles).Include(m => m.AccountProfile).ToList();

This code will not work because I need to do Select(m => new AccountVM() {...}) which is not code efficient, because I have to assign each of the properties.

So is there a way to do this?

---

Updated

So I just figurred out a little change in my view model into:

[NotMapped]
public class AccountVM : Account
{
    public string Name { get { return base.AccountProfile.Name; } set { base.AccountProfile.Name = value; } }
}

and my retriever:

List<AccountVM> models = db.Accounts.Include(m => m.Roles).Include(m => m.AccountProfile).Select(m => m as AccountVM).ToList();

Then another error arise:

The 'TypeAs' expression with an input of type 'Yountrep.Models.Account' and a check of type 'Yountrep.ViewModels.AccountVM' is not supported. Only entity types and complex types are supported in LINQ to Entities queries.

I guess the problem is now how to typecast it into AccountVM

Answer 1

Your view model should not be inheriting from an entity model. You can create your view model like this to include any relational objects.

public class AccountVM
{
    public string Name { get; set; }
    public AccountProfile Profile { get; set; }

    public class AccountProfile
    {
        public string Name { get; set; }
    }
}

You can than manually copy over the properties when building your LINQ query:

List<AccountVM> vm = db.Accounts.Select(a => 
{ 
    new AccountVM {
        Name= a.Name,
        Profile = new AccountProfile {
            Name = a.AccountProfile.Name
        }    
    }
}).ToList();

Another alternative is to use AutoMapper. I use AutoMapper for several of my projects, and it reduces the need to have to manually translate every field.

AutoMapper

If you want to flatten properties:

    public class AccountVM
    {
        public string Name { get; set; }
        public string ProfileName { get; set; }
    }

List<AccountVM> vm = db.Accounts.Select(a => 
{ 
    new AccountVM {
        Name= a.Name,
        ProfileName = (a.AccountProfile == null) ? "" : a.AccountProfile.Name
       }    
    }
}).ToList();

I also added a ternary expression to check for null. This will avoid an exception error if profile does not exist.