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

    public class Product
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Description { get; set; }

        public virtual WarrantyCard WarrantyCard { get; set; }
    }

    public class WarrantyCard
    {
        public int ProductId { get; set; }
        public DateTime ExpiredDate { get; set; }

        public virtual Product Product { get; set; }
    }

2、创建EntityContext类并继承DbContext

    public class EntityContext : DbContext
    {
        public EntityContext()
            : base("name=DBConnectionString")
        {

        }

        public DbSet<Product> Product { get; set; }
        public DbSet<WarrantyCard> WarrantyCard { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Configurations.AddFromAssembly(Assembly.GetExecutingAssembly());
            base.OnModelCreating(modelBuilder);
        }

 3、在web.config文件中添加数据库连接字符串

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

 4、创建表映射类

    public class ProductMap : EntityTypeConfiguration<Product>
    {
        public ProductMap()
        {
            ToTable("Product");
            HasKey(p => p.Id);

            //两条语句效果一样
            HasOptional(p => p.WarrantyCard).WithRequired(p => p.Product);
            //HasRequired(p => p.WarrantyCard).WithRequiredPrincipal(i => i.Product);
        }
    }

    public class WarrantyCardMap : EntityTypeConfiguration<WarrantyCard>
    {
        public WarrantyCardMap()
        {
            ToTable("WarrantyCard");
            HasKey(w => w.ProductId);
        }
    }

 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

    EntityContext db = new EntityContext();
    var product = new Product() { Description = "电器", Name = "电磁炉" };
    db.Set<Product>().Add(product);
    db.SaveChanges();

    var card = new WarrantyCard() { ExpiredDate = DateTime.Now, ProductId = product.Id };
    db.Set<WarrantyCard>().Add(card);
    db.SaveChanges();

    //WarrantyCard为Product类中的WarrantyCard属性名
    var list = db.Set<Product>().Include("WarrantyCard").ToList();

 6、数据库关系图