使用 LINQ 执行 GroupBy 和 Union 来获取记录

Question

情况是这样的。

我正在尝试使用 LINQ 在两个查询之间执行 Union。我在两个查询中都应用了 GroupBy，使用的是匿名类型。我不太清楚，但可能是匿名类型的使用导致我无法执行该 Union 操作的问题。它向我显示了这样的异常：

'System.Linq.IQueryable' does not contain a definition for 'Union' and the best extension method overload 'System.Linq.ParallelEnumerable.Union(System.Linq.ParallelQuery, System.Collections.Generic.IEnumerable)' has some invalid arguments

这里是查询：

var records = (from o in _context.Table1
                       join q in _context.Table2 on o.UserId equals q.UserId
                       group new { o, q }
                       by new { o.Name, o.Date, o.IsDone, o.IsDl, o.DateChanged, o.UserId, q.FirstName, q.LastName } into data
                       select new
                       {
                           NameP = data.Key.Name,
                           Date = data.Key.Date,
                           IsDone = data.Key.IsDone,
                           IsDl = data.Key.IsDl,
                           DateDone = data.Key.DateChanged,
                           Name = data.Key.FirstName +" "+ data.Key.LastName
                       }).Union(
                            from i in _context.Table1
                            where i.UserId == null
                            group i by new {o.Name, o.Date, o.IsDone, o.IsDl, o.DateChanged, o.UserId} into newData
                            select new
                            {
                                NameP = newData.Key.Name,
                                Date= newData.Key.Date,
                                IsDone = newData.Key.IsDone,
                                IsDl = newData.Key.IsDl,
                                DateDone = ' ',
                                Name = ' '
                            }).ToList();

我在这里想要实现的是获取两种情况的记录，当 UserId 为 null 时以及当它不为 null 时使用 group by 因为记录是重复的。

如有任何关于我做错的建议或指导，我们将不胜感激。

Answer 1

确保所有属性的两个匿名类型具有相同的数据类型。

我唯一可以推测的是日期。也许第一个 DateDone 实际上是 DateTime 类型，而您将第二个设置为 string...

var records = (from o in _context.Table1
               join q in _context.Table2 on o.UserId equals q.UserId
               group new { o, q }
               by new 
               { 
                   o.Name, 
                   o.Date,  
                   o.IsDone,  
                   o.IsDl,  
                   o.DateChanged,  
                   o.UserId,  
                   q.FirstName,  
                   q.LastName  
               } into data
               select new
               {
                   NameP = data.Key.Name,
                   Date = data.Key.Date,
                   IsDone = data.Key.IsDone,
                   IsDl = data.Key.IsDl,
                   DateDone = data.Key.DateChanged,
                   Name = data.Key.FirstName +" "+ data.Key.LastName
               }).Union(from i in _context.Table1
                        where i.UserId == null
                        group i by new 
                        {
                            o.Name,
                            o.Date, 
                            o.IsDone, 
                            o.IsDl, 
                            o.DateChanged, 
                            o.UserId
                        } into newData
                        select new
                        {
                            NameP = newData.Key.Name,
                            Date = newData.Key.Date,
                            IsDone = newData.Key.IsDone,
                            IsDl = newData.Key.IsDl,
                            DateDone = new DateTime(0),
                            Name = ' '
                        }).ToList();

使用 LINQ 执行 GroupBy 和 Union 来获取记录

Performing GroupBy and Union using LINQ to fetch records

c#

linq

asp.net-mvc

union

group-by