如何使用自定义 class 作为具有 Entity Framework Core 转换的实体的属性？

Question

I am trying to model various levels of accounts using "Table Per Hierarchy" in my application. Basically there are 3 levels of account: Super, Partner and Standard. They all share most of their properties, but the key difference is that Standard accounts are managed by a Super or Partner account.

I want to add an AccountType property to the Account base class that is a custom class, but is persisted to the database as a string. I know you can add a conversion for properties via EF's fluent API, but I cannot get it to work for this scenario.

This is how my classes are laid out:

 public abstract class Account { [Key] public int Id { get; set; } [Required] public AccountTypeClass AccountType { get; set; } // other props omitted for brevity } public class StandardAccount: Account { [Required] public int ManagingAccountId { get; set; } [ForeignKey(nameof(ManagingAccountId))] public ManagingAccount ManagingAccount { get; set; } } public abstract class ManagingAccount: Account { public ICollection<StandardAccount> Accounts { get; set; } = new List<StandardAccount>(); } public class PartnerAccount: ManagingAccount { } public class SuperAccount: ManagingAccount { } public class AccountTypeClass { // other props omitted for brevity private string value; private AccountTypeClass(string value) => this.value = value; public static AccountTypeClass Super => new AccountTypeClass(nameof(Super).ToLower()); public static AccountTypeClass Partner => new AccountTypeClass(nameof(Partner).ToLower()); public static AccountTypeClass Standard => new AccountTypeClass(nameof(Standard).ToLower()); public static AccountTypeClass Parse(string value) { switch(value) { case "super": return Super; case "partner": return Partner; case "standard": return Standard; default: throw new NotImplementedException(); } } public override string ToString() => this.value; }

And this is my DbContext :

 public class DataContext: DbContext { public DataContext(DbContextOptions options): base(options) { } public virtual DbSet<Account> Accounts { get; set; } protected override void OnModelCreating(ModelBuilder builder) { base.OnModelCreating(builder); builder.Entity<Account>().Property(p => p.AccountType).HasConversion(p => p.ToString(), p => AccountTypeClass.Parse(p)); builder.Entity<SuperAccount>().HasData(new SuperAccount() { Id = 1 }); builder.Entity<PartnerAccount>().HasData(new PartnerAccount() { Id = 2 }); builder.Entity<StandardAccount>().HasData(new StandardAccount() { Id = 3, ManagingAccountId = 1 }); } }

When I try and add a migration I get the following error message:

The property or navigation 'AccountType' cannot be added to the entity type 'ManagingAccount' because a property or navigation with the same name already exists on entity type 'Account'.

But if I swap out the AccountTypeClass for this enum:

 public enum AccountTypeEnum { Super, Partner, Standard }

And change the conversion to this (Where EnumHelper is just a little helper class that parses a string to an enum value):

 builder.Entity<Account>().Property(p => p.AccountType).HasConversion(p => p.ToString(), p => EnumHelper.Parse<AccountTypeEnum>(p));

Everything works as expected.

I can get the conversion to/from my AccountTypeClass to work on a standalone class (no inheritance), but not when I try using inheritance and table per hierarchy. Is this not supported or have I done something wrong?

Answer 1

I could be wrong, but I feel like your migrations are messed up right now. Have you tried deleting all your migrations and creating a fresh initial migration, just to verify your model is translatable?