EF Core为分组依据生成错误的SQL

Question

我在ASP.NET Core Web API中关注LINQ查询：

var _accountId = 101;

var textChatRecords = (from message in _dbContext.Messages
 join user in _dbContext.User on new { message.AccountId, message.UserId }
 equals new { user.AccountId, user.UserId }
 where message.AccountId == _accountId
 group new { message, user } by new { message.UserId, user.UserIdentifier } into g
 select new ReturnModel
 {
     UserId = g.FirstOrDefault().user.UserId,
     UserName = g.FirstOrDefault().user.UserName,
     UnReadCount = g.Count(x => !x.message.IsRead),
     SortID = g.Max(x => x.message.TextChatLogId),
     UserIdentifier = g.FirstOrDefault().user.UserIdentifier,
     UserFirstName = g.FirstOrDefault().user.UserName,
     UserLastName = g.FirstOrDefault().user.UserName
 }).OrderByDescending(x => x.SortID);

稍后在代码中，我正在

returnModel = returnModel.Where(x => x.UserName.Contains(request.userName));

但是我发现，即使SQL Server中的字段不区分大小写，上一行中的Contains()也是区分大小写的。

这使我得出结论，该查询是在C＃端而不是在SQL Server中执行的。 因此，我打开了SQL事件探查器，并检查了正在执行的查询。 这是哪个：

exec sp_executesql N'SELECT [message].[AccountId], [message].[TextChatLogId], [message].[CommunicationLogId], [message].[CreatedBy], [message].[CreatedOn], [message].[Direction], [message].[IsRead], [message].[LastUpdatedBy], [message].[LastUpdatedOn], [message].[Message], [message].[UserId], [message].[RowVersionStamp], [user].[AccountId], [user].[UserId], [user].[AddressLine1], [user].[AddressLine2], [user].[Age], [user].[City], [user].[CreatedDate], [user].[DefaultHygenistId], [user].[DefaultLocationId], [user].[DefaultProviderId], [user].[Email], [user].[EmailNotification], [user].[FirstName], [user].[Gender], [user].[IsActive], [user].[LastName], [user].[Mobile], [user].[UserIdentifier], [user].[UserName], [user].[PhoneWithExt], [user].[PostalNotification], [user].[PreferredContactTextMedium], [user].[PreferredContactVoiceMedium], [user].[PromotionEmailNotification], [user].[RelationshipToResponsibleParty], [user].[ResponsiblePartyUserId], [user].[State], [user].[TextNotification], [user].[Type], [user].[VoiceNotification], [user].[WorkPhoneWithExt], [user].[ZipCode]
FROM [pat_eng].[Messages] AS [message]
INNER JOIN [pat_eng].[User] AS [user] ON ([message].[AccountId] = [user].[AccountId]) AND ([message].[UserId] = [user].[UserId])
WHERE [message].[AccountId] = @___accountId_0
ORDER BY [message].[UserId], [user].[UserIdentifier]',N'@___accountId_0 int',@___accountId_0=101

此SQL查询没有我用C＃代码编写的任何group by或Contains。

为什么我的LINQ被翻译成错误的SQL？