Question

我有一个产品（草稿）列表，需要与数据库匹配（保存）并进行一些计算。当我们检索或创建时，它们是相同的对象。如果我将Reference1（草稿）与Reference1（已保存）和Reference2（草稿）与Reference2（已保存）匹配，那么它会很顺利，但是他们更改了数据库表并且还必须修改Object，其中，它们可以覆盖Reference1使用OverrideReference1字段的值。 OverrideReference1是在Reference1上使用的高优先级（如果不是空的）。我也使用string.IsNullOrEmpty(s.OverrideReference1) ? s.Reference1 : s.OverrideReference1加入但没有运气

我使用以下代码查询结果，但在加入两个对象时出错。

        var draft = new List<Product>
        {
            new Product { ProductName ="Phone", Quantity = 1000, Reference1 = "RC1", OverrideReference1 = string.Empty, Status = "Draft", Reference2 = string.Empty },
            new Product { ProductName ="Phone", Quantity = 2000, Reference1 = "RC2", OverrideReference1 = string.Empty, Status = "Draft", Reference2 = string.Empty  },
            new Product { ProductName ="Phone", Quantity = 3000, Reference1 = "RC3", OverrideReference1 = string.Empty, Status = "Draft", Reference2 = string.Empty  },
            new Product { ProductName ="Phone", Quantity = 3000, Reference1 = string.Empty, OverrideReference1 = string.Empty, Status = "Draft", Reference2 = "CC1"  },
        };

        var saved = new List<Product>
        {
            new Product { ProductName ="Phone", Quantity = 500, Reference1 = "RC1", OverrideReference1 = "RC3", Status = "Saved" },
            new Product { ProductName ="Phone", Quantity = 3000, Reference1 = string.Empty, OverrideReference1 = string.Empty, Status = "Saved", Reference2 = "CC1"  },
        };

        var results = (from d in draft
                       join s in saved on new { d.Reference1, d.Reference2 } equals new { s.OverrideReference1 ?? s.Reference1, s.Reference2 }
                       select new Product
                       {
                           ProductName = d.ProductName,
                           Quantity = s.Quantity - d.Quantity,
                           Reference1 = d.Reference1,
                           Status = d.Status
                       }).ToList();

Answer 1

当使用＆＃34; OverrideReference1＆＃34; 此属性时，

列名必须与您的问题相同。

此行中的问题：

    join s in saved on new { d.Reference1, d.Reference2 } equals 
new { s.OverrideReference1 ?? s.Reference1, s.Reference2 }

更新

join s in saved on new {
                        (string?)Reference1 = d.Reference1,
                        (string?)Reference2= d.Reference2 } equals 
                    new {(string?)Reference1 = s.OverrideReference1 ?? s.Reference1,
                         (string?)Reference2= s.Reference2 }

代码：

var results = (from d in draft
                   join s in saved on new {(string?)Reference1 = d.Reference1,(string?)Reference2= d.Reference2 } equals 
                   new {(string?)Reference1 = s.OverrideReference1 ?? s.Reference1,(string?)Reference2= s.Reference2 }
                   select new Product
                   {
                       ProductName = d.ProductName,
                       Quantity = s.Quantity - d.Quantity,
                       Reference1 = d.Reference1,
                       Status = d.Status
                   }).ToList();

LINQ：在引用

1 个答案: