EF Code-First 學習之旅 配置一對一的關係

1對一、1對0 的關係

例如：Entity1與零個或一個Entity2的實例有關係

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; }
}

 

在關係型數據庫（如SQL Server）中，1對0或1的關係是一個表的主鍵將是另外一個關係表的主鍵或外鍵

所以，建立Student表的時候設置StudentId爲主鍵，StudentAddress表的StudentAddressId既是主鍵有事外鍵

在Code First默認約定中，StudentId屬性默認爲Student的主鍵，StudentAddressId默認爲StudentAddress的主鍵，所以，咱們只須要配置StudentAddressId又爲外鍵就行

經過以下配置便可

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也能夠保存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做爲外鍵

 

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); 

}

 

 

一對一的關係

一對一在MS SQL Server中在技術上是不可能的，它老是1對0或1的關係，EF是在實體上表現爲一對一的關係，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)代表Address屬性是必須的

.WithRequiredPrincipal(ad => ad.Student)

注：主實體是Student，依賴實體是StudentAddress