Question

我在EF v4中遇到麻烦。我知道这个问题非常受欢迎，我试图在互联网上找到一些东西，但它没有帮助。我有类与地址（人有地址）一对一的人

class Person
{
public int PersonId{get;set;}
public string FisrtName{get; set;}
...
public int AddressId{get;set;}
public virtual Address Address{get;set;}
}
class Address
{
public int AddressId{get;set}
public string Street{get;set;}
...
}

我认为它是一对一的关系，我遵循EF v4中的所有约定。但是当我创建生成DB的DB图时，我看不到Person和Address之间的任何关系。我的意思是我看到两个表没有关系上的人和关键字地址另一个像这种关系的表创建了一对多的Account上的键和地址上的无穷大，但代码相同。我在设计师看到只有一对多的关联，有些情况我可以看到表之间的任何关系必须是。请帮帮我！谢谢你的帮助 P.S我认为添加表格时设计师遇到了麻烦

Answer 1

如果您首先使用代码，则可以使用流畅的代码API或使用属性来优化模型来自定义持久性映射。如果您要使用简单的密钥名称（例如Id），EF可以通过推理来解决关系;在你的情况下，EF需要提示PersonID和AddressID是密钥。

要使用属性方法，请在项目中添加对System.ComponentModel.DataAnnotations的引用，并使用System.ComponentModel.DataAnnotations添加对应的＆＃39;＆＃39;在您的源文件中根据需要。以下示例（EF 4.3.1）将生成＆＃34;一对多＆＃34;生成的地址和人员表之间的关系（在这种情况下，您不希望一对一）。运行代码后，您将在SQL Server数据库关系图窗口中看到关系。

class Program
{
    static void Main(string[] args)
    {
        using (ContactsEntities entities = new ContactsEntities())
        {
            Address doeaddress = new Address() { Street = "1 Broadway", ZipCode = "01234" };
            Address doeaddress2 = new Address() { Street = "2 Broadway", ZipCode = "01234" };
            entities.Addresses.Add(doeaddress);
            entities.Persons.Add(new Person() { FirstName = "Jane", LastName = "Doe", Address = doeaddress });
            entities.Persons.Add(new Person() { FirstName = "John", LastName = "Doe", Address = doeaddress });
            entities.Persons.Add(new Person() { FirstName = "Jim", LastName = "Doe", Address = doeaddress2 });
            entities.SaveChanges(); 
        }
        Console.WriteLine("Press Enter to exit...");
        Console.ReadLine();

    }
}

[Table("Addresses")]
public partial class Address
{
    public Address()
    {
        this.Persons = new HashSet<Person>();
    }
    [Key]
    public int AddressID { get; set; }
    [Required]
    public string Street { get; set; }
    [RegularExpression(@"^(\d{5}-\d{4}|\d{5}|\d{9})$")]
    [Required]
    public string ZipCode { get; set; }

    public virtual ICollection<Person> Persons { get; set; }
}

[Table("Persons")]
public partial class Person
{
    [Key]
    public int PersonID { get; set; }
    public int AddressID { get; set; }
    [Required]
    public string FirstName { get; set; }
    [Required]
    public string LastName { get; set; }
    [ForeignKey("AddressID")]
    public virtual Address Address { get; set; }
}

public partial class ContactsEntities : DbContext
{
    public DbSet<Address> Addresses { get; set; }
    public DbSet<Person> Persons { get; set; }
}

Answer 2

根据反馈，这里是一对一（实际上是一对一或一对）关系的示例。我使用了流畅的API来设置OnModelCreating覆盖中的关系。在这种情况下，一个人最多可以有一个照片行。实际上，如果Photos表包含一个或多个用于保存图像数据的大字节数组，这可能很有用;为清晰起见，我使用字符串来表示图像的链接。

    static void Main(string[] args)
    {
        using (ContactsEntities entities = new ContactsEntities())
        {

            entities.Persons.Add(new Person() { FirstName = "Jane", LastName = "Doe", Photo = new Photo() { PhotoLink = "/images/jane.jpg" } });
            entities.Persons.Add(new Person() { FirstName = "John", LastName = "Doe" }); // no photo
            entities.Persons.Add(new Person() { FirstName = "Joe", LastName = "Smith", Photo = new Photo() { PhotoLink = "/images/joe.jpg", ThumnbnailLink = "/images/thumbs/joe.jpg" } });

            // note that the following is not allowed based on the defined RI rules - will fail on call to SaveChanges:
            // entities.Photos.Add(new Photo() { PhotoLink = "/images/as.jpg" });

            entities.SaveChanges();

            foreach (Person person in entities.Persons)
            {
                Console.WriteLine("{0} {1} {2}", person.FirstName, person.LastName, person.Photo == null ? "missing photo" : person.Photo.PhotoLink);
            } 
        }

        Console.WriteLine("Press Enter to exit...");
        Console.ReadLine();

    }
}

public partial class ContactsEntities : DbContext
{
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        // a Person may have at most one Photo
        modelBuilder.Entity<Person>().HasOptional<Photo>(p => p.Photo);
        // a Photo is dependant on a Person (non-nullable FK constraint)
        modelBuilder.Entity<Photo>().HasRequired<Person>(p => p.Person);
        base.OnModelCreating(modelBuilder);
    }
    public DbSet<Photo> Photos { get; set; }
    public DbSet<Person> Persons { get; set; }
}

[Table("Photos")]
public partial class Photo
{
    [Key]
    public int PhotoID { get; set; }
    [Required]
    public string PhotoLink { get; set; }
    public string ThumnbnailLink { get; set; }
    public virtual Person Person { get; set; }
}

[Table("Persons")]
public partial class Person
{
    [Key]
    public int PersonID { get; set; }
    [Required]
    public string FirstName { get; set; }
    [Required]
    public string LastName { get; set; }

    public virtual Photo Photo { get; set; }
}

实体框架中的关系问题

2 个答案: