SQL to Linq 按计数分组

Question

我在表中有一个列来计算特定行。 sql查询如下：

SELECT
    CASE
    WHEN trail LIKE 'ClassA%'   THEN 'ClassA'
    WHEN trail LIKE 'ClassB%' THEN 'ClassB'
    WHEN trail LIKE 'SemA%' THEN 'SemesterA'
    WHEN trail LIKE 'SemB%' THEN 'SemesterB'
  END AS Logs
, COUNT(*) AS Count
FROM Logs where s_date >= 'from date from UI' and e_date <= 'to date from ui'
GROUP BY 
  CASE
    WHEN trail LIKE 'ClassA%'   THEN 'ClassA'
    WHEN trail LIKE 'ClassB%' THEN 'ClassB'
    WHEN trail LIKE 'SemA%' THEN 'SemesterA'
    WHEN trail LIKE 'SemB%' THEN 'SemesterB'
END

上面的查询结果sql很好

ClassA 20
ClassB 5
SemesterA 2
SemesterB 50

现在，我需要使用日期过滤器（从日期到日期）将此 sql 更改为 Linq。 请建议更改查询以简化它。 谢谢

试过了：-

var data = _db.Logs.Where(p => p.trail.StartsWith("ClassA") && (p.SDate.Date >= CDate.Date && p.SDate.Date <= FDate.Date)).GroupBy(p => p.trail.StartsWith("ClassA")).Select(s =>
            new
            {
                source = "Class - A total",
                percentage = s.Count()

            }).Union(_db.Logs.Where(p => p.trail.StartsWith("ClassB") && (p.SDate.Date >= CDate.Date && p.SDate.Date <= FDate.Date)).GroupBy(p => p.trail.StartsWith("ClassB")).Select(s =>
            new
            {
                source = "Class - B total",
                percentage = s.Count()

            }).Union(_db.Logs.Where(p => p.trail.StartsWith("SemesterA") && (p.SDate.Date >= CDate.Date && p.SDate.Date <= FDate.Date)).GroupBy(p => p.trail.StartsWith("SemesterA")).Select(s =>
            new
            {
                source = "Semester - A total",
                percentage = s.Count()

            }).Union(_db.Logs.Where(p => p.trail.StartsWith("SemesterB") && (p.SDate.Date >= CDate.Date && p.SDate.Date <= FDate.Date)).GroupBy(p => p.trail.StartsWith("SemesterB")).Select(s =>
            new
            {
                source = "Semester - B total",
                percentage = s.Count()

            })))).ToList();

Answer 1

尝试将所有有趣的起始键存储在某种枚举中，然后使用内置的 group by 方法重载，它输出从键、组对映射的结果（c.f. https://msdn.microsoft.com/en-us/library/vstudio/bb549393(v=vs.100).aspx）

string[] startingKeys = new string[] {"ClassA","ClassB","SemsterA","SemesterB"};

var data =_db.Logs.Where(p=>(p.SDate.Date >= CDate.Date && p.SDate.Date <= FDate.Date)&&startingKeys.Any(k=>p.Logs.StartsWith(k))).GroupBy(p=>startingKeys.Where(k=>p.Logs.StartsWith(k)).First(),(key,items)=>new {source=key,count = items.Count()})

此方法的一个优点是您可以在运行时更改启动键，如果您愿意的话。