我有一个嵌套数据模型,我想从中获取按顶级属性分组的聚合数据。 例如我的模型:
public class Scan {
public long Id {get; set;}
public int ProjectId { get; set; }
public int ScanUserId { get; set; }
public ICollection<ScanItem>? Items { get; set; }
}
public class ScanItem
{
public long Id { get; set; }
public long InventoryScanId { get; set; }
public double Qty { get; set; }
}
我想获取按 Scan.ScanUserId 分组的所有扫描,然后获取每个用户的 ScanItems.Qty 的总和。我的查询看起来像这样,EF 给出了以下错误:
Processing of the LINQ expression 'AsQueryable((Unhandled parameter: x).Items)' by 'NavigationExpandingExpressionVisitor' failed
from scan in Scans
.Include(x=>x.ScanUser)
.Include(x=>x.Items)
group scan by new { scan.ScanUser.Name, scan.ScanUser.Id } into g
select new
{
UserId = g.Key.Id,
Name = g.Key.Name,
LastSyncTime = g.Max(x => x.ScanDate),
ScanItems = g.Sum(x=>x.Items.Sum(i=>i.Qty))
}
如何在不在客户端评估的情况下对嵌套表的属性运行聚合函数?
最佳答案
EF Core 仍然无法翻译 GroupBy
结果(分组)上的嵌套聚合。
您必须使用 GroupBy
的元素选择器(或查询语法中的 element
group element by key
)预先计算嵌套聚合>):
from scan in Scans
group new { scan.ScanDate, Qty = scan.Items.Sum(i => i.Qty) } // <--
by new { scan.ScanUser.Name, scan.ScanUser.Id } into g
select new
{
UserId = g.Key.Id,
Name = g.Key.Name,
LastSyncTime = g.Max(x => x.ScanDate),
ScanItems = g.Sum(x => x.Qty) // <--
}
**更新:**对于 SqlServer,上面的 LINQ 查询转换为 SQL 查询,如下所示:
SELECT [s1].[Id] AS [UserId], [s1].[Name], MAX([s0].[ScanDate]) AS [LastSyncTime], SUM((
SELECT SUM([s].[Qty])
FROM [ScanItem] AS [s]
WHERE [s0].[Id] = [s].[InventoryScanId])) AS [ScanItems]
FROM [Scan] AS [s0]
INNER JOIN [ScanUser] AS [s1] ON [s0].[ScanUserId] = [s1].[Id]
GROUP BY [s1].[Name], [s1].[Id]
如评论中所述,它会生成 SQL 执行异常“无法对包含聚合或子查询的表达式执行聚合函数。”。
因此您确实需要另一种方法 - 使用 left join
在分组之前展平结果集,然后对该集执行分组/聚合:
from scan in Scans
from item in scan.Items.DefaultIfEmpty() // <-- left outer join
group new { scan, item } by new { scan.ScanUser.Name, scan.ScanUser.Id } into g
select new
{
UserId = g.Key.Id,
Name = g.Key.Name,
LastSyncTime = g.Max(x => x.scan.ScanDate),
ScanItems = g.Sum(x => (double?)x.item.Qty) ?? 0
};
现在转换为有效的 SqlServer SQL 查询:
SELECT [s1].[Id] AS [UserId], [s1].[Name], MAX([s].[ScanDate]) AS [LastSyncTime], COALESCE(SUM([s0].[Qty]), 0.0E0) AS [ScanItems]
FROM [Scan] AS [s]
LEFT JOIN [ScanItem] AS [s0] ON [s].[Id] = [s0].[InventoryScanId]
INNER JOIN [ScanUser] AS [s1] ON [s].[ScanUserId] = [s1].[Id]
GROUP BY [s1].[Name], [s1].[Id]
关于c# - ef-core 嵌套表聚合函数给出 "NavigationExpandingExpressionVisitor failed",我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/59735196/