EntityFramework之一对一关系（二）

下面新建两个实体，关系为一对一

Product为产品类，WarrantyCard为保修卡类，一个产品对应一个保修卡，一个保修卡对应一个产品。

1、新建实体类

 1     public class Product
 2     {
 3         public int Id { get; set; }
 4         public string Name { get; set; }
 5         public string Description { get; set; }
 6 
 7         public virtual WarrantyCard WarrantyCard { get; set; }
 8     }
 9 
10     public class WarrantyCard
11     {
12         public int ProductId { get; set; }
13         public DateTime ExpiredDate { get; set; }
14 
15         public virtual Product Product { get; set; }
16     }

2、创建EntityContext类并继承DbContext

 1     public class EntityContext : DbContext
 2     {
 3         public EntityContext()
 4             : base("name=DBConnectionString")
 5         {
 6 
 7         }
 8 
 9         public DbSet<Product> Product { get; set; }
10         public DbSet<WarrantyCard> WarrantyCard { get; set; }
11 
12         protected override void OnModelCreating(DbModelBuilder modelBuilder)
13         {
14             modelBuilder.Configurations.AddFromAssembly(Assembly.GetExecutingAssembly());
15             base.OnModelCreating(modelBuilder);
16         }

3、在web.config文件中添加数据库连接字符串

1 <connectionStrings>
2     <add name="DBConnectionString" connectionString="Data Source=.;Initial Catalog=OneToOne;Integrated Security=true" providerName="System.Data.SqlClient" />
3 </connectionStrings>

4、创建表映射类

 1     public class ProductMap : EntityTypeConfiguration<Product>
 2     {
 3         public ProductMap()
 4         {
 5             ToTable("Product");
 6             HasKey(p => p.Id);
 7 
 8             //两条语句效果一样
 9             HasOptional(p => p.WarrantyCard).WithRequired(p => p.Product);
10             //HasRequired(p => p.WarrantyCard).WithRequiredPrincipal(i => i.Product);
11         }
12     }
13 
14     public class WarrantyCardMap : EntityTypeConfiguration<WarrantyCard>
15     {
16         public WarrantyCardMap()
17         {
18             ToTable("WarrantyCard");
19             HasKey(w => w.ProductId);
20         }
21     }

HasOptional(p => p.WarrantyCard).WithRequired(p => p.Product)这句大概意思是：在新增数据到Product表时可以不加数据到WarrantyCard表，也可以加，

但是往WarrantyCard表新增数据时必须有Product表中的ProductId，WarrantyCard依赖Product，生成的是关系是Product表Id是主键，WarrantyCard表ProductId是外键。

5、写点代码测试一下

 1     EntityContext db = new EntityContext();
 2     var product = new Product() { Description = "电器", Name = "电磁炉" };
 3     db.Set<Product>().Add(product);
 4     db.SaveChanges();
 5 
 6     var card = new WarrantyCard() { ExpiredDate = DateTime.Now, ProductId = product.Id };
 7     db.Set<WarrantyCard>().Add(card);
 8     db.SaveChanges();
 9 
10     //WarrantyCard为Product类中的WarrantyCard属性名
11     var list = db.Set<Product>().Include("WarrantyCard").ToList();

6、数据库关系图