实体框架自定义数据类型映射

Question

给定以下代码：

public class Car 
{
    public virtual int CarId { get; set; }
    public virtual string TypeName { get; set; }
    public ConvertableNullable<double> Price { get; set; }
}

其中 ConvertableNullable 只是 Nullable 的解决方法，但它不会从中继承。

现在，这是我的简单上下文，我将汽车类映射到实体，并映射它的每个属性

public class MyDBContext : DbContext {
   public MyDBContext() : base(
       "data source=.;initial catalog=newDB1;integrated security=True;" + 
        "multipleactiveresultsets=True;App=EntityFramework")
   { }

   protected override void OnModelCreating(DbModelBuilder modelBuilder)
   {
       base.OnModelCreating(modelBuilder);

       modelBuilder.Entity<Car>().HasKey(x=>x.CarId);
       modelBuilder.Entity<Car>().Property(x => x.TypeName);
       modelBuilder.Entity<Car>().Property(x => x.Price);
   }

    public DbSet<Car> Cars { get; set; }
}

，当我尝试处理这个上下文时，它会抛出异常

var db = new MyDBContext();

// Throws exception "The property 'Price' is not a declared 
// property on type 'Car'. Verify that the property has not
// been explicitly excluded from the model by using the Ignore
// method or NotMappedAttribute data annotation. Make sure that
// it is a valid primitive property."
var c = db.Cars.ToList(); 

有什么建议吗？

Answer 1

唯一的解决方案是使用这样的东西：

public class Car 
{
    public virtual int CarId { get; set; }
    public virtual string TypeName { get; set; }
    // This must be accessible to the mapping 
    public double? PriceData { get; set; } 

    public ConvertableNullable<double> Price 
    { 
        get { // Return data from PriceData }
        set { // Set data to PriceData }
    }
}

您的映射将是：

modelBuilder.Entity<Car>().HasKey(x=>x.CarId);
modelBuilder.Entity<Car>().Property(x => x.TypeName);
modelBuilder.Entity<Car>().Property(x => x.PriceData).HasColumnName("Price");
modelBuilder.Entity<Car>().Ignore(x => x.Price);

问题是 EF 全局不支持自定义标量类型。

Answer 2

“确保它是一个有效的原始属性” - 显然问题出在你的 Nullable 解决方法上 - 为什么不把它变成一个可以为 null 的双精度呢？

public class Car 
{
    public virtual int CarId { get; set; }
    public virtual string TypeName { get; set; }
    public double? Price { get; set; }
}