UPDATE：从EF7 preview 7开始，现在只需使用string.Joinnormally作为示例：

_context.MyTable
    .GroupBy(keySelector => keySelector.MyKey, elemSelector => elemSelector.StringProp)
    .Select(elem => string.Join(',', elem))
   //.FirstOrDefaultAsync(cancellationToken), if (keyselector => 1) i.e. only 1 group so you get all rows

"旧答案"
好吧，根据这个this issue，string.Join（）还没有实现（到现在为止），IEnumerable.Aggregate也不会转换。

• 同时 *，您可以创建一个视图并在其中编写SQL。例如，按id和string分组。Join（“，“，Names）;

CREATE VIEW V_Name AS
SELECT ID,  
Names=STUFF  
(  
    (  
      SELECT DISTINCT ' || '+ CAST(Child.Name AS VARCHAR(MAX))  
      FROM Child,MainTable
      WHERE Main.ID= t1.ID --this line is imp...
      AND Child.ID=MainTable.ID
      FOR XMl PATH('')  
    ),1,1,''  
)  
FROM MainTable t1 
GROUP BY t1.IDReview

或

CREATE VIEW V_Name AS
SELECT ID, STRING_AGG(Name, ', ') AS Names
FROM MainTable
LEFT JOIN ChildTable ON MainTable.ID = ChildTable.ID
GROUP BY ID

现在，在C#中，您可以简单地将它与您的ID连接起来，就像您通常使用IQueryable一样：

from data in _dbcontext.sometable
       join groupedAndJoinedNames in _dbcontext.viewname
                on data.ID equals groupedAndJoinedNames.ID
       select new
       {
            Names = groupedAndJoinedNames.Names
       }