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Я застрял с проблемой производительности с EF.

         using (var context = new CustomDbContext())
        {
            var result = context.
                TransactionLines
                .Where(x => 
                    x.Transaction.TransactionTypeId == 1433 amp;amp;
                    (x.Transaction.Eob.EobBatchId == null || x.Transaction.Eob.EobBatch.Status == EobBatchStatusEnum.Completed)
                )
                .GroupBy(x => x.VisitLine.ProcedureId)
                .Select(x => new
                {
                    Id = x.Key,
                    PaidAmount = x.Sum(t => t.PaidAmount),
                    Code = context.Procedures.Where(h => h.Id == x.Key).Select(h => h.Code).FirstOrDefault()
                }).ToArray();
        }
  

EF генерирует следующий sql:

 SELECT 
1 AS [C1], 
[Project6].[ProcedureId] AS [ProcedureId], 
[Project6].[C2] AS [C2], 
[Project6].[C1] AS [C3]
FROM ( SELECT 
    [Project5].[ProcedureId] AS [ProcedureId], 
    [Project5].[C1] AS [C1], 
    (SELECT 
        SUM([Extent7].[PaidAmount]) AS [A1]
        FROM     [dbo].[TransactionLines] AS [Extent7]
        INNER JOIN [dbo].[Transactions] AS [Extent8] ON [Extent7].[TransactionId] = [Extent8].[Id]
        LEFT OUTER JOIN [dbo].[Eobs] AS [Extent9] ON [Extent8].[EobId] = [Extent9].[Id]
        LEFT OUTER JOIN [dbo].[EobBatches] AS [Extent10] ON [Extent9].[EobBatchId] = [Extent10].[Id]
        LEFT OUTER JOIN [dbo].[VisitLines] AS [Extent11] ON [Extent7].[VisitLineId] = [Extent11].[Id]
        WHERE (([Extent9].[EobBatchId] IS NULL) OR (1 = [Extent10].[Status])) AND ([Extent8].[TransactionTypeId] = 1433) AND (([Project5].[ProcedureId] = [Extent11].[ProcedureId]) OR (([Project5].[ProcedureId] IS NULL) AND ([Extent11].[ProcedureId] IS NULL)))) AS [C2]
    FROM ( SELECT 
        [Project4].[ProcedureId] AS [ProcedureId], 
        [Project4].[C1] AS [C1]
        FROM ( SELECT 
            [Project2].[ProcedureId] AS [ProcedureId], 
            (SELECT TOP (1) 
                [Extent6].[Code] AS [Code]
                FROM [dbo].[Procedures] AS [Extent6]
                WHERE [Extent6].[Id] = [Project2].[ProcedureId]) AS [C1]
            FROM ( SELECT 
                [Distinct1].[ProcedureId] AS [ProcedureId]
                FROM ( SELECT DISTINCT 
                    [Extent5].[ProcedureId] AS [ProcedureId]
                    FROM     [dbo].[TransactionLines] AS [Extent1]
                    INNER JOIN [dbo].[Transactions] AS [Extent2] ON [Extent1].[TransactionId] = [Extent2].[Id]
                    LEFT OUTER JOIN [dbo].[Eobs] AS [Extent3] ON [Extent2].[EobId] = [Extent3].[Id]
                    LEFT OUTER JOIN [dbo].[EobBatches] AS [Extent4] ON [Extent3].[EobBatchId] = [Extent4].[Id]
                    LEFT OUTER JOIN [dbo].[VisitLines] AS [Extent5] ON [Extent1].[VisitLineId] = [Extent5].[Id]
                    WHERE (([Extent3].[EobBatchId] IS NULL) OR (1 = [Extent4].[Status])) AND ([Extent2].[TransactionTypeId] = 1433)
                )  AS [Distinct1]
            )  AS [Project2]
        )  AS [Project4]
    )  AS [Project5]
)  AS [Project6]
  

Продолжительность запроса составляет ~ 3 секунды.
Если написать sql-запрос напрямую, используя Group, то длительность запроса составляет 1,5 секунды, и он использует вдвое меньше ресурсов процессора.

     SELECT sq.ProcedureId, SUM(sq.PaidAmount), (SELECT TOP(1) Procedures.Code From Procedures Where Procedures.Id = sq.ProcedureId) as Code
FROM(
    SELECT [Extent5].[ProcedureId] AS [ProcedureId],[Extent1].PaidAmount as [PaidAmount]
    FROM     [dbo].[TransactionLines] AS [Extent1]
    INNER JOIN [dbo].[Transactions] AS [Extent2] ON [Extent1].[TransactionId] = [Extent2].[Id]
    LEFT OUTER JOIN [dbo].[Eobs] AS [Extent3] ON [Extent2].[EobId] = [Extent3].[Id]
    LEFT OUTER JOIN [dbo].[EobBatches] AS [Extent4] ON [Extent3].[EobBatchId] = [Extent4].[Id]
    LEFT OUTER JOIN [dbo].[VisitLines] AS [Extent5] ON [Extent1].[VisitLineId] = [Extent5].[Id]
    WHERE (([Extent3].[EobBatchId] IS NULL) OR (1 = [Extent4].[Status])) AND ([Extent2].[TransactionTypeId] = 1433)
) sq
GROUP BY sq.ProcedureId
  

Я написал разные linq, но все еще не могу заставить EF генерировать GroupBy вместо подзапросов.
В идеале я бы не хотел использовать функции или написанный вручную sql, потому что у меня много условий при построении логики linq.

Можно ли заставить EF генерировать SQL точно так, как он был написан в linq?

Попробуйте избежать

 context.Procedures.Where(h => h.Id == x.Key).Select(h => h.Code).FirstOrDefault()
  

включив Code в GroupBy предложение — я знаю, что это кажется избыточным, но известно, что у EF возникают проблемы с переводом операций группировки, которые включают что-то другое, кроме использования средств доступа к ключам и агрегатов:

 //...
.GroupBy(x => new { Id = x.VisitLine.ProcedureId, x.VisitLine.Procedure.Code })
.Select(x => new
{
    Id = x.Key.Id,
    PaidAmount = x.Sum(t => t.PaidAmount),
    Code = x.Key.Code
}).ToArray();
  

Обновление: приведенное выше генерирует следующий SQL в моей тестовой среде (последняя версия EF6.1.3):

 SELECT
    1 AS [C1],
    [GroupBy1].[K1] AS [ProcedureId],
    [GroupBy1].[A1] AS [C2],
    [GroupBy1].[K2] AS [Code]
    FROM ( SELECT
        [Extent5].[ProcedureId] AS [K1],
        [Extent6].[Code] AS [K2],
        SUM([Filter1].[PaidAmount]) AS [A1]
        FROM    (SELECT [Extent1].[VisitLineId] AS [VisitLineId], [Extent1].[PaidAmount] AS [PaidAmount]
            FROM    [dbo].[TransactionLine] AS [Extent1]
            INNER JOIN [dbo].[Transaction] AS [Extent2] ON [Extent1].[TransactionId] = [Extent2].[Id]
            LEFT OUTER JOIN [dbo].[Eob] AS [Extent3] ON [Extent2].[EobId] = [Extent3].[Id]
            LEFT OUTER JOIN [dbo].[EobBatch] AS [Extent4] ON [Extent3].[EobBatchId] = [Extent4].[Id]
            WHERE (1433 = [Extent2].[TransactionTypeId]) AND ([Extent3].[EobBatchId] IS NULL OR [Extent4].[Status] = 1) ) AS [Filter1]
        LEFT OUTER JOIN [dbo].[VisitLine] AS [Extent5] ON [Filter1].[VisitLineId] = [Extent5].[Id]
        LEFT OUTER JOIN [dbo].[Procedure] AS [Extent6] ON [Extent5].[ProcedureId] = [Extent6].[Id]
        GROUP BY [Extent5].[ProcedureId], [Extent6].[Code]
    )  AS [GroupBy1]
  

что намного лучше, как я и ожидал.

Обновление 2: EF — странный зверь. Использование двойной проекции дает желаемый результат:

 //...
.GroupBy(x => x.VisitLine.ProcedureId)
.Select(x => new
{
    Id = x.Key,
    PaidAmount = x.Sum(t => t.PaidAmount),
})
.Select(x => new
{
    x.Id,
    x.PaidAmount,
    Code = context.Procedures.Where(h => h.Id == x.Id).Select(h => h.Code).FirstOrDefault()
}).ToArray();
  

что приводит к следующему:

 SELECT
    1 AS [C1],
    [Project2].[ProcedureId] AS [ProcedureId],
    [Project2].[C1] AS [C2],
    [Project2].[C2] AS [C3]
    FROM ( SELECT
        [GroupBy1].[A1] AS [C1],
        [GroupBy1].[K1] AS [ProcedureId],
        (SELECT TOP (1)
            [Extent6].[Code] AS [Code]
            FROM [dbo].[Procedure] AS [Extent6]
            WHERE [Extent6].[Id] = [GroupBy1].[K1]) AS [C2]
        FROM ( SELECT
            [Extent5].[ProcedureId] AS [K1],
            SUM([Filter1].[PaidAmount]) AS [A1]
            FROM   (SELECT [Extent1].[VisitLineId] AS [VisitLineId], [Extent1].[PaidAmount] AS [PaidAmount]
                FROM    [dbo].[TransactionLine] AS [Extent1]
                INNER JOIN [dbo].[Transaction] AS [Extent2] ON [Extent1].[TransactionId] = [Extent2].[Id]
                LEFT OUTER JOIN [dbo].[Eob] AS [Extent3] ON [Extent2].[EobId] = [Extent3].[Id]
                LEFT OUTER JOIN [dbo].[EobBatch] AS [Extent4] ON [Extent3].[EobBatchId] = [Extent4].[Id]
                WHERE (1433 = [Extent2].[TransactionTypeId]) AND ([Extent3].[EobBatchId] IS NULL OR [Extent4].[Status] = 1) ) AS [Filter1]
            LEFT OUTER JOIN [dbo].[VisitLine] AS [Extent5] ON [Filter1].[VisitLineId] = [Extent5].[Id]
            GROUP BY [Extent5].[ProcedureId]
        )  AS [GroupBy1]
    )  AS [Project2]
  

PS Если это неясно, ответ на ваш конкретный вопрос

Можно ли заставить EF генерировать SQL точно так, как он был написан в linq?

нет. Напротив, вы должны написать запрос LINQ определенным образом, чтобы получить желаемый (или более близкий) SQL-запрос.