EF Code-First 學習之旅 配置一對一的關系

1對1、1對0 的關系

例如：Entity1與零個或一個Entity2的實例有關系

public class Student
{
    public Student() { }

    public int StudentId { get; set; }
    public string StudentName { get; set; }

    public virtual StudentAddress Address { get; set; }

}
     
public class StudentAddress 
{
    public int StudentAddressId { get; set; }
        
    public string Address1 { get; set; }
    public string Address2 { get; set; }
    public string City { get; set; }
    public int Zipcode { get; set; }
    public string State { get; set; }
    public string Country { get; set; }

    public virtual Student Student { get; set; }
}

 

在關系型數據庫（如SQL Server）中，1對0或1的關系是一個表的主鍵將是另一個關系表的主鍵或外鍵

因此，創建Student表的時候設置StudentId為主鍵，StudentAddress表的StudentAddressId既是主鍵有事外鍵

在Code First默認約定中，StudentId屬性默認為Student的主鍵，StudentAddressId默認為StudentAddress的主鍵，因此，我們只需要配置StudentAddressId又為外鍵就行

通過如下配置即可

public class Student
{
    public Student() { }

    public int StudentId { get; set; }
    public string StudentName { get; set; }

    public virtual StudentAddress Address { get; set; }

}
     
public class StudentAddress 
{
    [ForeignKey("Student")]
    public int StudentAddressId { get; set; }
        
    public string Address1 { get; set; }
    public string Address2 { get; set; }
    public string City { get; set; }
    public int Zipcode { get; set; }
    public string State { get; set; }
    public string Country { get; set; }

    public virtual Student Student { get; set; }
}

public class Student
{
    public Student() { }

    public int StudentId { get; set; }
    public string StudentName { get; set; }

    public virtual StudentAddress Address { get; set; }

}
     
public class StudentAddress 
{
    [Key, ForeignKey("Student")]
    public int StudentId { get; set; }
        
    public string Address1 { get; set; }
    public string Address2 { get; set; }
    public string City { get; set; }
    public int Zipcode { get; set; }
    public string State { get; set; }
    public string Country { get; set; }

    public virtual Student Student { get; set; }
}

 

Fluent API配置

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    
    // Configure Student & StudentAddress entity
    modelBuilder.Entity<Student>()
                .HasOptional(s => s.Address) // Mark Address property optional in Student entity
                .WithRequired(ad => ad.Student); // mark Student property as required in StudentAddress entity. Cannot save StudentAddress without Student

}

 

上面的配置說明：StudentAddress在Student中的導航屬性是可選的（沒有StudentAddress也可以保存Student），Student在StudentAddress中的導航屬性是必須的（沒有Student的話StudentAddress保存不了），StudentAddressId作為外鍵

 

public class Student
{
    public Student() { }

    public int StudentId { get; set; }
    public string StudentName { get; set; }

    public virtual StudentAddress Address { get; set; }

}
     
public class StudentAddress 
{
    public int StudentId { get; set; }
        
    public string Address1 { get; set; }
    public string Address2 { get; set; }
    public string City { get; set; }
    public int Zipcode { get; set; }
    public string State { get; set; }
    public string Country { get; set; }

    public virtual Student Student { get; set; }
}

 

 

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    // Configure StudentId as PK for StudentAddress
    modelBuilder.Entity<StudentAddress>()
        .HasKey(e => e.StudentId);
        
    // Configure StudentId as FK for StudentAddress
    modelBuilder.Entity<Student>()
                .HasOptional(s => s.Address) 
                .WithRequired(ad => ad.StudentId); 

}

 

 

一對一的關系

一對一在MS SQL Server中在技術上是不可能的，它總是1對0或1的關系，EF是在實體上表現為一對一的關系，而不是在數據庫中

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    // Configure StudentId as PK for StudentAddress
    modelBuilder.Entity<StudentAddress>()
        .HasKey(e => e.StudentId);
        
    // Configure StudentId as FK for StudentAddress
    modelBuilder.Entity<Student>()
                .HasRequired(s => s.Address) 
                .WithRequiredPrincipal(ad => ad.Student); 

}

 

 

modelBuilder.Entity<Student>().HasRequired(s => s.Address)表明Address屬性是必須的

.WithRequiredPrincipal(ad => ad.Student)

注：主實體是Student，依賴實體是StudentAddress