Question

我正在构建一个步骤跟踪Web应用程序。我正在使用最新的EF Core。我正在与三个表进行交互：

wg：WellnessGroup（WellnessGroupId，Name）
wgu：WellnessGroupUser（查询表：WellnessGroupId，EmployeeId）
wsl：WellnessStepsLog（EmployeeId，StepCount）

我想要的是获得所有WellnessGroups以及该组的总步数。如果还没有附加到该组的步骤，我希望NULL值为0.我有这个SQL语句，它给了我所需的数据：

SELECT wg.Name, SUM(ISNULL(wsl.StepCount, 0)) AS steps
FROM dbo.WellnessGroup AS wg
LEFT JOIN dbo.WellnessGroupUser AS wgu
ON wgu.WellnessGroupId = wg.Id
LEFT JOIN dbo.WellnessStepsLog AS wsl
ON wsl.EmployeeId = wgu.AzureAdUserId
GROUP BY wg.Name
ORDER BY steps DESC;

我已经设法在我的控制器上放了两个LINQ表达式，它只给我一些与它们相关联的步骤的WellnessGroups，并且如果没有步骤则不给我WellnessGroup数据：

 var query = _dbContext.WellnessGroupUser
                    .Include(x => x.WellnessGroup)
                .Join(_dbContext.WellnessStepsLog, group => 
                group.AzureAdUserId, steps => steps.EmployeeId,
                    (group, steps) => new
                    {
                        Steps = steps.StepCount,
                        Date = steps.TrackedDate,
                        Group = group.WellnessGroup.Name

                    }).Where(x => x.Date >= yearToDate).Where(x => x.Date <= endDate);

 var stepsByGroup = query
                .GroupBy(x => x.Group)
                .Select(s => new
                {
                    Group = s.Key,
                    Date = s.Max(x => x.Date),
                    Steps = s.Sum(x => x.Steps)
                });

Answer 1

一种方法是查询所有WellnessGroups并将内部构建为第二个子查询。像这样：

var query =
    db.WellnessGroup.Select(wg => new {
        wg.WellnessGroupId,
        sum = (int?) wg.WellnessGroupUser
                       .Sum(wgu => wgu.Employee.WellnessStepsLog.Sum(wsl => wsl.StepCount))
    });

注意，转换为（int？）很重要。否则，sum假定为int，如果没有行的总和，则会导致InvalidOperationException。

另一种方法是首先构建所有总和。然后使用WellnessGroups进行外部联接：

// sum up all stepcounts
var q1 =
    from wgu in db.WellnessGroupUser
    from wsl in db.WellnessStepsLog
    where wgu.EmployeeId == wsl.EmployeeId
    group wsl.StepCount by wgu.WellnessGroupId
    into g
    select new {WellnessGroupId = g.Key, Sum = g.Sum()};

// join with all WellnessGroups
var q2 =
    from wg in db.WellnessGroup
    join s in q1 on wg.WellnessGroupId equals s.WellnessGroupId into sj
    from sum in sj.DefaultIfEmpty()
    select new {wg, sum = (int?) sum.Sum};

编辑：

由于OP后来在评论中询问如何按多个字段进行分组。以下是按WellnessGroup.WellnessGroupId和WellnessStepsLog.TrackedDate月份分组的示例。 GroupBy中的字段可以放在new { ... }中，可以有多个字段。因此，第一个查询为每个可能的WellnessGroup / Month组合创建一个行。第二个查询与之前一样执行WellnessGroup的外连接：

var q1 =
    from wgu in db.WellnessGroupUser
    from wsl in db.WellnessStepsLog
    where wgu.EmployeeId == wsl.EmployeeId
    group wsl.StepCount by new { wgu.WellnessGroupId, wsl.TrackedDate.Month }
    into g
    select new {g.Key.WellnessGroupId, g.Key.Month, Sum = g.Sum()};

// join with all WellnessGroups
var q2 =
    from wg in db.WellnessGroup
    join s in q1 on wg.WellnessGroupId equals s.WellnessGroupId into sj
    from sum in sj.DefaultIfEmpty()
    select new {wg.WellnessGroupId, Month = (int?) sum.Month, Sum = (int?) sum.Sum};

使用LINQ表达式进行多个左连接并使用ISNULL功能

1 个答案: