EntityFramework之一對一關系（二）

下面新建兩個實體，關系為一對一

Product為產品類，WarrantyCard為保修卡類，一個產品對應一個保修卡，一個保修卡對應一個產品。

1、新建實體類

    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、創建EntityContext類並繼承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文件中添加數據庫連接字符串

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

 4、創建表映射類

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

            //兩條語句效果一樣
            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)這句大概意思是：在新增數據到Product表時可以不加數據到WarrantyCard表，也可以加，

但是往WarrantyCard表新增數據時必須有Product表中的ProductId，WarrantyCard依賴Product，生成的是關系是Product表Id是主鍵，WarrantyCard表ProductId是外鍵。

5、寫點代碼測試一下

    EntityContext db = new EntityContext();
    var product = new Product() { Description = "電器", Name = "電磁爐" };
    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為Product類中的WarrantyCard屬性名
    var list = db.Set<Product>().Include("WarrantyCard").ToList();

 6、數據庫關系圖