无法将类型“System.Collections.Generic.List<AnonymousType#1>”隐式转换为“System.Collections.Generic.List<AnonymousType#2>”[重复]

Question

我正面临一个编译时错误，例如

Cannot implicitly convert type 'System.Collections.Generic.List<AnonymousType#1>' to 'System.Collections.Generic.List<AnonymousType#2>'

这是我的代码：

var query = Enumerable.Repeat(new
            {
                        Id = default(int),
                        Name = string.Empty,
                        type_id = default(int),
                        Ownername = string.Empty,
                        Ownermob = string.Empty,
                        ContactPerson = string.Empty,
                        ContactPersonmob = string.Empty,
                        Phone = string.Empty,
                        Mobile = string.Empty,
                        Room = string.Empty,
                        Build = string.Empty,
                        Road = string.Empty,
                        Area = string.Empty,
                        City = string.Empty,
                        country_id = default(int?),
                        state_id = default(int?),
                        Email = string.Empty,
                        Remark = string.Empty,
                        UserOFC = default(bool),
                        UserVAT = default(bool),
                        UserINV = default(bool),
                        UserNone = default(bool),
                        Username = string.Empty,
                        Register_Date = default(DateTime)},0).ToList();

                    query = db.Parties.Where(p => p.type_id.Equals(GroupByENTYPE)).OrderByDescending(p => p.Register_Date).Select(p => new
                    {
                        Id = p.Id,
                        Name = p.Name,
                        type_id = p.type_id,
                        Ownername = p.Ownername,
                        Ownermob = p.Ownermob,
                        ContactPerson = p.ContactPerson,
                        ContactPersonmob = p.ContactPersonmob,
                        Phone = p.Phone,
                        Mobile = p.Mobile,
                        Room = p.Room,
                        Build = p.Build,
                        Road = p.Road,
                        Area = p.Area,
                        City = p.City,
                        country_id = p.country_id,
                        state_id = p.state_id,
                        Email = p.Email,
                        Remark = p.Remark,
                        UserOFC = p.UserOFC,
                        UserVAT = p.UserVAT,
                        UserINV = p.UserINV,
                        UserNone = p.UserNone,
                        Username = db.Users.Where(u => u.Ref_no.Equals(p.User_id)).Select(u => u.Username).FirstOrDefault(),
                        Register_Date = p.Register_Date
                    }).FilterForColumn(ColumnName, SearchText).ToList();//here error occurs
                }

这里用于声明公共查询部分并在多个条件下分配它。在 FilterColumn 部分面临编译时错误。如何在另一个页面上使用相同类型的此声明不会产生任何问题。

我在这里放置了提供知识的表模式：

---------------------已更新--------- -------------------

Id  int Unchecked
Name    varchar(50) Unchecked
type_id int Unchecked
Ownername   varchar(50) Checked
Ownermob    nchar(10)   Checked
Room    varchar(10) Checked
Build   varchar(50) Checked
Road    text    Checked
Area    text    Checked
City    varchar(50) Checked
Phone   nchar(10)   Checked
Mobile  nchar(10)   Checked
Email   varchar(100)    Checked
ContactPerson   varchar(50) Checked
ContactPersonmob    nchar(10)   Checked
UserOFC bit Checked
UserVAT bit Checked
UserINV bit Checked
UserNone    bit Checked
state_id    int Checked
country_id  int Checked
Remark  text    Checked
Register_Date   smalldatetime   Unchecked
User_id char(14)    Unchecked

请帮帮我...

Answer 1

很难从纯文本中看出。尝试使用二进制搜索来查找不兼容的属性。那就是

1. 注释掉后半部分属性以查看前半部分属性中是否发生不兼容。
2. 如果编译器仍然报告错误，请对前半部分属性执行相同操作。
3. 如果编译器不报告错误，则对后半部分属性执行相同操作。

Answer 2

你的匿名类型的属性看起来是一样的，所以我最好的猜测是，当你有一个对象要使用时，你的默认类型之一与实际使用的类型不同。

我认为解决这个问题的最佳策略是使用 Null Object pattern

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资源：

• 你可以看this不错的教程。
• Tutorial + example