LINQ:连接两个对象，引用合并

Question

我有一个产品列表(草案)，需要与数据库(已保存)进行匹配并进行一些计算。当我们检索或创建时，它们是相同的对象。如果我将Reference1 (draft)匹配到Reference1 (saved)，将Reference2(draft)匹配到Reference2(saved)，则一切顺利，但是它们修改了数据库表，并且还必须修改Object，其中，它们可以通过使用overriderreference1字段覆盖Reference1值。overriderreference1是在Reference1之上使用的高优先级(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

我使用下面的代码来查询结果，但是在连接两个对象时出现错误。

        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

列名必须设置相同，您的问题是当字符串为空时使用"OverrideReference1"此属性。

本行问题:

    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();