遵循DDD方式如何更新EF Core 2.0拥有的实体？

Question

我有一个项目在遵循DDD方法的情况下使用Asp.Net Core 2.0。 因此，我拥有聚合的根，这些根拥有实体和值对象，这些对象和值对象被配置为拥有的类型，这是EF Core 2.0中的一项新功能。 我添加了这样的配置示例以更好地阐明。

域：

public class Address : ValueObject 
{
    public Address(string street, int number){
        Street = street;
        Number = number;
    }

    public string Street {get; private set;}
    public int Number {get; private set;}
}  
public class Company : AggregateRoot
{
    public Address Address {get; private set;}
    // Other properties...

    // Value objects are immutables so I'm only able to replace it with a new object.
    public void UpdateAddress(string street, int number){
        Address = new Address(street, number);
    }
    // Other methods...
}

EF核心实体配置：

internal class CompanyEntityTypeConfiguration : IEntityTypeConfiguration<Company>
{
    public void Configure(EntityTypeBuilder<Company> builder)
    {
        builder.HasKey(x => x.Id);
        builder.OwnsOne(x => x.Address);
    }
}

我正在从数据库中检索跟踪实体，当我尝试更新AggregateRoot并将其替换为一个新的值对象时，出现一个异常，提示“另一个相同类型的实体已被跟踪”。 地址是被跟踪的实体。

因此，解决方案是检索未跟踪的内容，但我不想使用此方法，因为它将在数据库中进行完整的更新。 那么，如何从Entity Framework 2.0跟踪的实体更新值对象（拥有的实体）？

Answer 1

使用ef core 1.0.0时，我找到了一种解决方法。 我再也找不到参考资料来将链接放在此处，并感谢作者，但是，在您的情况下，解决方法如下：

领域 ：

public class Address : ValueObject
    {
        public Address(string street, int number)
        {
            Street = street;
            Number = number;
        }

        public string Street { get; private set; }
        public int Number { get; private set; }


        #region Value object workaround
        public Address WithStreet(string value) => new Address(value, Number);

        public Address WithNumber(int value) => new Address(Street, value);
        #endregion
    }
    public class Company : AggregateRoot
    {

        #region public public Address Address { get; set; }
        [NotMapped]
        public Address Address { get; set; }

        //In the DbContext this property needs to be mapped with a column in a database
        private string Address_Street
        {
            get { return Address.Street; }
            set { Address = Address.WithStreet(value); }
        }

        //In the DbContext this property needs to be mapped with a column in a database
        private int Address_Number
        {
            get { return Address.Number; }
            set { Address = Address.WithNumber(value); }
        }
        #endregion


        // Other properties...

        // Value objects are immutables so I'm only able to replace it with a new object.
        public void UpdateAddress(string street, int number)
        {
            Address = new Address(street, number);
        }
        // Other methods...
    }

EF核心实体配置：

internal class CompanyEntityTypeConfiguration : IEntityTypeConfiguration<Company>
    {
        public void Configure(EntityTypeBuilder<Company> builder)
        {
            #region Address value object workaround
            builder.Property(typeof(string), "Address_Street").HasColumnName("Address_Street");
            builder.Property(typeof(int), "Address_Number").HasColumnName("Address_Number");
            #endregion
        }
    }

需要重写DbContext中的SaveChanges（）

DbContext：

public class YourDbContext : DbContext
    {
        //yours DbSet<>

        protected override void OnModelCreating(ModelBuilder builder)
        {
            //yours EntityTypeConfiguration
        }

        /// <summary>
        /// Overridden for value object workaround
        /// </summary>
        /// <returns></returns>
        public override int SaveChanges()
        {
            foreach (var entry in ChangeTracker.Entries())
            {
                foreach (var pi in entry.Entity.GetType().GetProperties(BindingFlags.Instance | BindingFlags.NonPublic))
                {
                    entry.Property(pi.Name).CurrentValue = pi.GetValue(entry.Entity);
                }
            }
            return base.SaveChanges();
        }
    }

如果ef core 2.0拥有的实体像EF6.X复杂类型那样工作，以实现DDD值对象，那将是很好的。 此解决方法将需要一些猴子作业代码，但您将能够应用DDD。