从事务日志中计算机架中的活动框

Question

我这里有2张桌子

机架

Id	RackName
1	Rack A
2	Rack B

机架交易

Id	RackId	Barcode	Event	DateTime
1	1	ABC1234	IN	2021-07-12
2	1	ABC1234	OUT	2021-07-20
3	1	ABC1235	IN	2021-07-21
4	1	ABC1236	IN	2021-07-21
5	1	ABC1236	OUT	2021-07-23
6	1	ABC1237	IN	2021-07-21
7	1	ABC1238	IN	2021-07-21
8	1	ABC1238	OUT	2021-07-23

条形码 ABC1235 和 ABC1237 尚未签出。所以 RACK A 内的总计数框是 2.

那么根据给定的示例数据，我如何使用 linq 生成？

var getTotal = await _context.RackBoxLogs.Where(c => c.RackId == rackId)
                                .GroupBy(c => new { c.Barcode,c.Event })
                                .Select(g => new { g.Key, MaxDate = g.Max(c => c.CreatedOn),Event = g.Key.Event })
                                .Where(c=> c.Event == "IN")
                                .CountAsync();

即使我已经按条形码分组并过滤了最大日期，我仍然得到错误的结果。有什么想法吗？

Answer 1

我认为这应该适用于 EF 5。不幸的是 EF 5 不能（还）翻译 GroupBy().Select(g => g.Last()).

var getTotal = RackTransaction
                .Where(rt => rt.RackId == rackId)
                .Select(rt => rt.Barcode)
                .Distinct()
                .Select(b => RackTransaction.Where(rt => rt.Barcode == b).OrderBy(rt => rt.DateTime).Last())
                .Where(rt => rt.Event == "IN")
                .Count();

Answer 2

此查询应获得所需的计数：

var getTotal = await _context.RackBoxLogs
    .Where(c => c.RackId == rackId)
    .GroupBy(c => new { c.Barcode })
    .Where(g => g.Sum(x => x.Event == "IN"  ? 1 : 0) > 
                g.Sum(x => x.Event == "OUT" ? 1 : 0)
    )
    .CountAsync();

从事务日志中计算机架中的活动框

Count active boxes in the rack from transaction logs

c#

linq

postgresql

ef-core-3.1