EF Code First 学习笔记:关系

一对多关系

项目中最常用到的就是一对多关系了。Code First对一对多关系也有着很好的支持。很多情况下我们都不需要特意的去配置，Code First就能通过一些引用属性、导航属性等检测到模型之间的关系，自动为我们生成外键。观察下面的类：

public class Destination
{
public int DestinationId { get; set; }
public string Name { get; set; }
public string Country { get; set; }
public string Description { get; set; }
public byte[] Photo { get; set; }
public List<Lodging> Lodgings { get; set; }
}

public class Lodging
{
public int LodgingId { get; set; }
public string Name { get; set; }
public string Owner { get; set; }
public bool IsResort { get; set; }
public decimal MilesFromNearestAirport { get; set; }
public Destination Destination { get; set; }
}

public class Destination
{
public int DestinationId { get; set; }
public string Name { get; set; }
public string Country { get; set; }
public string Description { get; set; }
public byte[] Photo { get; set; }
}

public class Lodging
{
public int LodgingId { get; set; }
public string Name { get; set; }
public string Owner { get; set; }
public bool IsResort { get; set; }
public decimal MilesFromNearestAirport { get; set; }
public Destination Destination { get; set; }
}

public class Destination
{
public int DestinationId { get; set; }
public string Name { get; set; }
public string Country { get; set; }
public string Description { get; set; }
public byte[] Photo { get; set; }
public List<Lodging> Lodgings { get; set; }
}

public class Lodging
{
public int LodgingId { get; set; }
public string Name { get; set; }
public string Owner { get; set; }
public bool IsResort { get; set; }
public decimal MilesFromNearestAirport { get; set; }
}

public class Destination
{
public int DestinationId { get; set; }
public string Name { get; set; }
public string Country { get; set; }
public string Description { get; set; }
public byte[] Photo { get; set; }
public List<Lodging> Lodgings { get; set; }
}

public class Lodging
{
public int LodgingId { get; set; }
public string Name { get; set; }
public string Owner { get; set; }
public bool IsResort { get; set; }
public decimal MilesFromNearestAirport { get; set; }
//外键
public int TargetDestinationId { get; set; }
public Destination Target { get; set; }
}

public class Lodging
{
public int LodgingId { get; set; }
public string Name { get; set; }
public string Owner { get; set; }
public bool IsResort { get; set; }
public decimal MilesFromNearestAirport { get; set; }
public Destination Target { get; set; }
//第一联系人
public Person PrimaryContact { get; set; }
//第二联系人
public Person SecondaryContact { get; set; }
}

public class Person
{
public int PersonID { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public List<Lodging> PrimaryContactFor { get; set; }
public List<Lodging> SecondaryContactFor { get; set; }
}

public class Lodging
{
public int LodgingId { get; set; }
public string Name { get; set; }
public string Owner { get; set; }
public bool IsResort { get; set; }
public decimal MilesFromNearestAirport { get; set; }
public Destination Target { get; set; }
//第一联系人
public Person PrimaryContact { get; set; }
//第二联系人
public Person SecondaryContact { get; set; }
}

public class Person
{
public int PersonID { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public List<Lodging> PrimaryContactFor { get; set; }
public List<Lodging> SecondaryContactFor { get; set; }
}

public class Person
{
public int PersonId { get; set; }
public int SocialSecurityNumber { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
[Timestamp]
public byte[] RowVersion { get; set; }
public PersonPhoto Photo { get; set; }
}

public class PersonPhoto
{
[Key]
public int PersonId { get; set; }
public byte[] Photo { get; set; }
public string Caption { get; set; }
public Person PhotoOf { get; set; }
}

public class Person { public int PersonId { get; set; } public int SocialSecurityNumber { get; set; } public string FirstName { get; set; } public string LastName { get; set; } [Timestamp] public byte[] RowVersion { get; set; } public PersonPhoto Photo { get; set; } } public class PersonPhoto { [Key, ForeignKey("PhotoOf")] public int PersonId { get; set; } public byte[] Photo { get; set; } public string Caption { get; set; } public Person PhotoOf { get; set; } }

public class Person
{
public int PersonId { get; set; }
public int SocialSecurityNumber { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
[Timestamp]
public byte[] RowVersion { get; set; }
public PersonPhoto Photo { get; set; }
}

public class PersonPhoto
{
[Key, ForeignKey("PhotoOf")]
public int PersonId { get; set; }
public byte[] Photo { get; set; }
public string Caption { get; set; }
public Person PhotoOf { get; set; }
}

使用Fluent API：

modelBuilder.Entity<PersonPhoto>().HasRequired(p => p.PhotoOf).WithOptional(p => p.Photo);

注意：PersonPhoto表中的PersonId既是外键也必须是主键

public class User
{
[Key]
public int UserId { get; set; }
public string UserName { get; set; }
public string Password { get; set; }
public bool IsActive { get; set; }
public System.DateTime CreateDate { get; set; }
public virtual Student Student { get; set; }
public virtual ICollection<Teacher> Teachers { get; set; }
public virtual UserDetail UserDetail { get; set; }
}

public class Teacher
{
[Key,ForeignKey("User")]
public int UserId { get; set; }
[Key, ForeignKey("Class")]
public int ClassId { get; set; }

[Key, ForeignKey("Course")]
public string CourseId { get; set; }

[Key, ForeignKey("Role")]
public int RoleId { get; set; }

public virtual Class Class { get; set; }
public virtual Course Course { get; set; }
public virtual Role Role { get; set; }
public virtual User User { get; set; }
}

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{

base.OnModelCreating(modelBuilder);
//一对一
modelBuilder.Entity<UserDetail>().HasRequired(p => p.User).WithOptional(p => p.UserDetail);
modelBuilder.Entity<Student>().HasRequired(p => p.User).WithOptional(p => p.Student);
//一对多
modelBuilder.Entity<Teacher>().HasKey(t => new { t.UserId, t.CourseId,t.ClassId,t.RoleId });
modelBuilder.Entity<Teacher>().HasRequired(p => p.User).WithMany(l => l.Teachers).HasForeignKey(p => p.UserId);
modelBuilder.Entity<Teacher>().HasRequired(p => p.Class).WithMany(l => l.Teachers).HasForeignKey(p => p.ClassId);
modelBuilder.Entity<Teacher>().HasRequired(p => p.Course).WithMany(l => l.Teachers).HasForeignKey(p => p.CourseId);
modelBuilder.Entity<Teacher>().HasRequired(p => p.Role).WithMany(l => l.Teachers).HasForeignKey(p => p.RoleId);
}