学步园

给实体的某一属性设置默认值

model： 

 

Weight为Product的一个可为空属性， 右击Weight，查看属性，Default Value中设置默认值。

 

            using (EFDemoEntities context = new EFDemoEntities())
            {
                Product product = new Product
                                      {
                                          ProductName = "大鸭梨",
                                          UnitPrice = 3,
                                          Color = "White"
                                      };
                context.Products.AddObject(product);
                context.SaveChanges();
            }

 

 

结果如下： 

 

 

查询时给为Null 的属性设置默认值 

            //Linq
            using (var context = new EFDemoEntities())
            {
                Console.WriteLine("Products:");
                var products = from p in context.Products
                           select new { ProductName = p.ProductName, Weight = p.Weight ?? 0 };
                foreach (var product in products)
                {
                    Console.WriteLine("{0}, 重量: {1}", product.ProductName, product.Weight);
                }
            }
            //Esql
            using (var context = new EFDemoEntities())
            {
                Console.WriteLine("Products:");
                string esql = @"select
                    p.ProductName,
                    case when p.Weight is null then 0
                    else p.Weight
                    end as ProductWeight
                    from Products as p";
                var products = context.CreateQuery<DbDataRecord>(esql);
                foreach (var product in products)
                {
                    Console.WriteLine("{0}, 重量: {1}", product.GetString(0), product.GetDouble(1));
                }
            }

 

 

结果如下(默认值为0)：