EF Core 2.1 支持数据库一对一关系

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CREATE TABLE [dbo].[Person](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [PersonCode] [nvarchar](50) NULL,
    [Name] [nvarchar](50) NULL,
    [Age] [int] NULL,
    [City] [nvarchar](50) NULL,
    [CreateTime] [datetime] NULL,
 CONSTRAINT [PK_Person] PRIMARY KEY CLUSTERED 
    [ID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY],
 CONSTRAINT [IX_Person] UNIQUE NONCLUSTERED 
    [PersonCode] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
ALTER TABLE [dbo].[Person] ADD  CONSTRAINT [DF_Person_CreateTime]  DEFAULT (getdate()) FOR [CreateTime]
从上面可以看出，除了主键ID外，我们还设置了列PersonCode为唯一键IX_Person。




    

然后数据库中还有张表IdentificationCard，其代表的是一个人的身份证，其中列IdentificationNo是身份证号码，其建表语句如下：
CREATE TABLE [dbo].[IdentificationCard](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [IdentificationNo] [nvarchar](50) NULL,
    [PersonCode] [nvarchar](50) NULL,
    [CreateTime] [datetime] NULL,
 CONSTRAINT [PK_IdentificationCard] PRIMARY KEY CLUSTERED 
    [ID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY],
 CONSTRAINT [IX_IdentificationCard] UNIQUE NONCLUSTERED 
    [PersonCode] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
ALTER TABLE [dbo].[IdentificationCard] ADD  CONSTRAINT [DF_IdentificationCard_CreateTime]  DEFAULT (getdate()) FOR [CreateTime]
ALTER TABLE [dbo].[IdentificationCard]  WITH CHECK ADD  CONSTRAINT [FK_IdentificationCard_Person] FOREIGN KEY([PersonCode])
REFERENCES [dbo].[Person] ([PersonCode])
ON UPDATE CASCADE
ON DELETE CASCADE
ALTER TABLE [dbo].[IdentificationCard] CHECK CONSTRAINT [FK_IdentificationCard_Person]
其中设置外键关系FK_IdentificationCard_Person：通过IdentificationCard表的PersonCode列来关联Person表的PersonCode列，从而指明一张身份证属于哪个Person。
然后我们同样设置了IdentificationCard表的PersonCode列为唯一键IX_IdentificationCard，这样外键FK_IdentificationCard_Person表示的实际上就是一对一关系了，因为IdentificationCard表的一行数据通过列PersonCode只能找到一行Person表数据，而现在IdentificationCard表的PersonCode列又是唯一键，所以反过来Person表在IdentificationCard表中最多也只能找到一行数据，所以这是个典型的一对一关系。
我们还在FK_IdentificationCard_Person外键关系上使用了CASCADE设置了级联删除和级联更新。
EF Core实体
接着我们新建了一个.NET Core控制台项目，使用EF Core的Scaffold-DbContext指令自动从数据库中生成实体，可以看到通过我们在数据库中设置的唯一键和外键，EF Core自动识别出了Person表和IdentificationCard表之间是一对一关系，生成的代码如下：
Person实体，对应的是数据库中的Person表，注意其中包含一个属性IdentificationCard，表示Person表和IdentificationCard表的一对一关系：
using System;
using System.Collections.Generic;
namespace FFCoreOneToOne.Entities
    /// <summary>
    /// Person实体，对应数据库中的Person表，可以看到其中有一个IdentificationCard属性，表示Person实体对应一个IdentificationCard实体
    /// </summary>
    public partial class Person
        public int Id { get; set; }
        public string PersonCode { get; set; }
        public string Name { get; set; }
        public int? Age { get; set; }
        public string City { get; set; }
        public DateTime? CreateTime { get; set; }
        public IdentificationCard IdentificationCard { get; set; }
IdentificationCard实体，对应的是数据库中的IdentificationCard表，注意其中包含一个属性PersonCodeNavigation，表示IdentificationCard表和Person表的一对一关系：




    

using System;
using System.Collections.Generic;
namespace FFCoreOneToOne.Entities
    /// <summary>
    /// IdentificationCard实体，对应数据库中的IdentificationCard表，可以看到其中有一个PersonCodeNavigation属性，表示IdentificationCard实体对应一个Person实体
    /// </summary>
    public partial class IdentificationCard
        public int Id { get; set; }
        public string IdentificationNo { get; set; }
        public string PersonCode { get; set; }
        public DateTime? CreateTime { get; set; }
        public Person PersonCodeNavigation { get; set; }
最后是Scaffold-DbContext指令生成的DbContext类TestDBContext，其中比较重要的地方是OnModelCreating方法中，设置IdentificationCard实体和Person实体间一对一关系的Fluent API代码，我用注释详细阐述了每一步的含义：
using System;
using FFCoreOneToOne.Logger;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata;
namespace FFCoreOneToOne.Entities
    public partial class TestDBContext : DbContext
        public TestDBContext()
        public TestDBContext(DbContextOptions<TestDBContext> options)
            : base(options)
        public virtual DbSet<IdentificationCard> IdentificationCard { get; set; }
        public virtual DbSet<Person> Person { get; set; }
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
            if (!optionsBuilder.IsConfigured)
                optionsBuilder.UseSqlServer("Server=localhost;User Id=sa;Password=1qaz!QAZ;Database=TestDB");
        protected override void OnModelCreating(ModelBuilder modelBuilder)
            modelBuilder.Entity<IdentificationCard>(entity =>
                entity.HasIndex(e => e.PersonCode)
                    .HasName("IX_IdentificationCard")
                    .IsUnique();
                entity.Property(e => e.Id).HasColumnName("ID");
                entity.Property(e => e.CreateTime)
                    .HasColumnType("datetime")
                    .HasDefaultValueSql("(getdate())");
                entity.Property(e => e.IdentificationNo).HasMaxLength(50);
                entity.Property(e => e.PersonCode).HasMaxLength(50);
                //设置IdentificationCard实体和Person实体的一对一关系
                entity.HasOne(d => d.PersonCodeNavigation)//HasOne设置IdentificationCard实体中有一个Person实体，可以通过IdentificationCard实体的PersonCodeNavigation属性访问到
                    .WithOne(p => p.IdentificationCard)//WithOne设置Person实体中有一个IdentificationCard实体，可以通过Person实体的IdentificationCard属性访问到
                    .HasPrincipalKey<Person>(p => p.PersonCode)//设置数据库中Person表的PersonCode列是一对一关系的主表键
                    .HasForeignKey<IdentificationCard>(d => d.PersonCode)//设置数据库中IdentificationCard表的PersonCode列是一对一关系的从表外键
                    .OnDelete(DeleteBehavior.Cascade)//由于我们在数据库中开启了IdentificationCard表外键FK_IdentificationCard_Person的级联删除，所以这里也生成了实体级联删除的Fluent API
                    .HasConstraintName("FK_IdentificationCard_Person");//设置IdentificationCard实体和Person实体的一对一关系采用的是数据库外键FK_IdentificationCard_Person
            modelBuilder.Entity<Person>(entity =>
                entity.HasIndex(e => e.PersonCode)
                    .HasName("IX_Person")
                    .IsUnique();
                entity.Property(e => e.Id).HasColumnName("ID");
                entity.Property(e => e.City).HasMaxLength(50);
                entity.Property(e => e.CreateTime)
                    .HasColumnType("datetime")
                    .HasDefaultValueSql("(getdate())");
                entity.Property(e => e.Name).HasMaxLength(50);
                entity.Property(e => e.PersonCode)
                    .IsRequired()
                    .HasMaxLength(50);
接着我们在.NET Core控制台项目的Program类中定义了些示例代码，其中AddPersonWithIdentificationCard和AddIdentificationCardWithPerson方法使用DbContext来添加数据到数据库，RemoveIdentificationCardFromPerson和RemovePersonFromIdentificationCard方法用来演示如何通过实体的导航属性来删除数据，最后DeleteAllPersons是清表语句，删除数据库中IdentificationCard表和Person表的所有数据。
这里先把示例代码全部贴出来：
using FFCoreOneToOne.Entities;
using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.Linq;
namespace FFCoreOneToOne
    class Program
        /// <summary>
        /// 删除数据库Person表和IdentificationCard表的所有数据
        /// </summary>
        static void DeleteAllPersons()
            using (TestDBContext dbContext = new TestDBContext())
                dbContext.Database.ExecuteSqlCommand("DELETE FROM [dbo].[IdentificationCard]");
                dbContext.Database.ExecuteSqlCommand("DELETE FROM [dbo].[Person]");
        /// <summary>
        /// 通过添加Person来添加IdentificationCard
        /// </summary>
        static void AddPersonWithIdentificationCard()
            //通过添加Person实体来添加IdentificationCard实体，将Person实体的IdentificationCard属性设置为对应的IdentificationCard实体即可
            using (TestDBContext dbContext = new TestDBContext())
                var james = new Person() { Name = "James", Age = 30, PersonCode = "P001", City = "Beijing" };
                james.IdentificationCard = new IdentificationCard() { IdentificationNo = "510100197512305607" };
                var tom = new Person() { Name = "Tom", Age = 35, PersonCode = "P002", City = "Shanghai" };
                tom.IdentificationCard = new IdentificationCard() { IdentificationNo = "510100197512305609" };
                var sam = new Person() { Name = "Sam", Age = 25, PersonCode = "P003", City = "Chongqing" };
                sam.IdentificationCard = new IdentificationCard() { IdentificationNo = "510100197512305605" };
                dbContext.Person.Add(james);
                dbContext.Person.Add(tom);
                dbContext.Person.Add(sam);
                dbContext.SaveChanges();
        /// <summary>
        /// 通过添加IdentificationCard来添加Person，从EF Core的日志中可以看到使用这种方式还是先执行的插入Person表数据的SQL，再执行的插入IdentificationCard表数据的SQL
        /// </summary>
        static void AddIdentificationCardWithPerson()
            //通过添加IdentificationCard实体来添加Person实体，将IdentificationCard实体的PersonCodeNavigation属性设置为对应的Person实体即可
            using (TestDBContext dbContext = new TestDBContext())
                var jamesCard = new IdentificationCard() { IdentificationNo = "510100197512305607" };
                jamesCard.PersonCodeNavigation = new Person() { Name = "James", Age = 30, PersonCode = "P001", City = "Beijing" };
                var tomCard = new IdentificationCard() { IdentificationNo = "510100197512305609" };
                tomCard.PersonCodeNavigation = new Person() { Name = "Tom", Age = 35, PersonCode = "P002", City = "Shanghai" };
                var samCard = new IdentificationCard() { IdentificationNo = "510100197512305605" };
                samCard.PersonCodeNavigation = new Person() { Name = "Sam", Age = 25, PersonCode = "P003", City = "Chongqing" };
                dbContext.IdentificationCard.Add(jamesCard);
                dbContext.IdentificationCard.Add(tomCard);
                dbContext.IdentificationCard.Add(samCard);
                dbContext.SaveChanges();
        /// <summary>
        /// 通过设置Person实体的IdentificationCard属性为null来删除IdentificationCard表的数据
        /// </summary>
        static void RemoveIdentificationCardFromPerson()
            //先用DbContext从数据库中查询出Person实体，然后设置其IdentificationCard属性为null，来删除IdentificationCard表的数据
            //注意在查询Person实体的时候，记得要用EF Core中Eager Loading的Include方法也查询出IdentificationCard实体，这样我们在设置Person实体的IdentificationCard属性为null后，DbContext才能跟踪到变更，才会在下面调用DbContext.SaveChanges方法时，生成删除IdentificationCard表数据的SQL语句
            using (TestDBContext dbContext = new TestDBContext())
                var james = dbContext.Person.Include(e => e.IdentificationCard).First(e => e.Name == "James");
                james.IdentificationCard = null;
                var tom = dbContext.Person.Include(e => e.IdentificationCard).First(e => e.Name == "Tom");
                tom.IdentificationCard = null;
                var sam = dbContext.Person.Include(e => e.IdentificationCard).First(e => e.Name == "Sam");
                sam.IdentificationCard = null;
                dbContext.SaveChanges();
        /// <summary>
        /// 本来这个方法是想用来通过设置IdentificationCard实体的PersonCodeNavigation属性为null，来删除Person表的数据，但是结果是还是删除的IdentificationCard表数据
        /// </summary>
        static void RemovePersonFromIdentificationCard()
            //原本我想的是，先用DbContext从数据库中查询出IdentificationCard实体，并用EF Core中Eager Loading的Include方法也查询出Person实体，然后设置IdentificationCard实体的PersonCodeNavigation属性为null，来删除Person表的数据
            //结果这样做EF Core最后还是删除的IdentificationCard表的数据，原因是IdentificationCard表是一对一外键关系的从表，设置从表实体的外键属性PersonCodeNavigation为null，EF Core认为的是从表的数据作废，所以删除了从表IdentificationCard中的数据，主表Person的数据还在。。。
            using (TestDBContext dbContext = new TestDBContext())
                var jamesCard = dbContext.IdentificationCard.Include(e => e.PersonCodeNavigation).First(e => e.IdentificationNo == "510100197512305607");
                jamesCard.PersonCodeNavigation = null;
                var tomCard = dbContext.IdentificationCard.Include(e => e.PersonCodeNavigation).First(e => e.IdentificationNo == "510100197512305609");
                tomCard.PersonCodeNavigation = null;
                var samCard = dbContext.IdentificationCard.Include(e => e.PersonCodeNavigation).First(e => e.IdentificationNo == "510100197512305605");
                samCard.PersonCodeNavigation = null;
                dbContext.SaveChanges();
        static void Main(string[] args)
            DeleteAllPersons();
            AddPersonWithIdentificationCard();
            AddIdentificationCardWithPerson();
            RemoveIdentificationCardFromPerson();
            RemovePersonFromIdentificationCard();
            Console.WriteLine("Press any key to quit...");
            Console.ReadKey();
AddPersonWithIdentificationCard
首先我们测试AddPersonWithIdentificationCard方法，其通过添加Person实体到数据库来添加IdentificationCard表的数据，更改Main方法的代码如下，并执行程序：
static void Main(string[] args)
    DeleteAllPersons();
    AddPersonWithIdentificationCard();
    //AddIdentificationCardWithPerson();
    //RemoveIdentificationCardFromPerson();
    //RemovePersonFromIdentificationCard();
    Console.WriteLine("Press any key to quit...");
    Console.ReadKey();
执行后数据库中Person表的数据如下：
IdentificationCard表的数据如下：
AddIdentificationCardWithPerson
然后我们测试AddIdentificationCardWithPerson方法，其通过添加IdentificationCard实体到数据库来添加Person表的数据，从EF Core的日志中可以看到使用这种方式还是先执行的插入Person表数据的SQL，再执行的插入IdentificationCard表数据的SQL。更改Main方法的代码如下，并执行程序：
static void Main(string[] args)
    DeleteAllPersons();
    //AddPersonWithIdentificationCard();
    AddIdentificationCardWithPerson();
    //RemoveIdentificationCardFromPerson();
    //RemovePersonFromIdentificationCard();
    Console.WriteLine("Press any key to quit...");
    Console.ReadKey();
执行后数据库中Person表的数据如下：
IdentificationCard表的数据如下：
RemoveIdentificationCardFromPerson
然后我们测试RemoveIdentificationCardFromPerson方法，其通过设置Person实体的IdentificationCard属性为null，来删除IdentificationCard表的数据，更改Main方法的代码如下，并执行程序：
static void Main(string[] args)
    DeleteAllPersons();
    AddPersonWithIdentificationCard();
    //AddIdentificationCardWithPerson();
    RemoveIdentificationCardFromPerson();
    //RemovePersonFromIdentificationCard();
    Console.WriteLine("Press any key to quit...");
    Console.ReadKey();
执行后数据库中Person表的数据如下：
IdentificationCard表的数据如下：
RemovePersonFromIdentificationCard
最后我们测试RemovePersonFromIdentificationCard方法，本来这个方法我是设计用来通过设置IdentificationCard实体的PersonCodeNavigation属性为null，来删除Person表的数据，但是测试后发现结果还是删除的IdentificationCard表的数据，原因可以看下上面示例代码中RemovePersonFromIdentificationCard方法中的注释。更改Main方法的代码如下，并执行程序：
static void Main(string[] args)
    DeleteAllPersons();
    AddPersonWithIdentificationCard();
    //AddIdentificationCardWithPerson();
    //RemoveIdentificationCardFromPerson();
    RemovePersonFromIdentificationCard();
    Console.WriteLine("Press any key to quit...");
    Console.ReadKey();
执行后数据库中Person表的数据如下：
IdentificationCard表的数据如下：