如何将此SQL查询转换为DotNet Core 2.1 Linq

以下是T-SQL：

SELECT 
    'Total Tournaments' AS Name, COUNT(a.location) AS Value
FROM
    (SELECT location
     FROM [dbo].[TournamentBatchItem]
     GROUP BY TournamentName, location) a

UNION

SELECT 
    'Outdoor Tournaments' AS Name, COUNT(a.location) AS Value
FROM
    (SELECT location
     FROM [dbo].[TournamentBatchItem]
     GROUP BY TournamentName, location) a
WHERE a.location = 'Outdoor'

UNION

SELECT 
    'Indoor Tournaments' AS Name, COUNT(a.location) AS Value
FROM
    (SELECT location
     FROM [dbo].[TournamentBatchItem]
     GROUP BY TournamentName, location) a
WHERE a.location = 'Indoor'

输出如下所示：

Name                | Value
--------------------+-------
Indoor Tournaments  |   0
Outdoor Tournaments |   1
TotalTournaments    |   1

var totalTournaments = (from tbi from _db.TournamentBatchItems select tbi.location).Count();
var whatever = (from tbi from _db.TournamentBatchItems where something==something select tbi.location).Count();

---

基本原理如下：

Name                | Value
--------------------+-------
Indoor Tournaments  |   0
Outdoor Tournaments |   1
TotalTournaments    |   1

var totalTournaments = (from tbi from _db.TournamentBatchItems select tbi.location).Count();
var whatever = (from tbi from _db.TournamentBatchItems where something==something select tbi.location).Count();

---

然后使用文本字符串“Total Tournaments”手动构建列表。（或使用union命令），但我的建议是只询问count，而不询问查询中的其他内容。

基本要求如下：

Name                | Value
--------------------+-------
Indoor Tournaments  |   0
Outdoor Tournaments |   1
TotalTournaments    |   1

var totalTournaments = (from tbi from _db.TournamentBatchItems select tbi.location).Count();
var whatever = (from tbi from _db.TournamentBatchItems where something==something select tbi.location).Count();

---

然后使用文本字符串“Total Tournaments”手动构建列表。（或使用union命令），但我的建议是只在查询中询问count而不询问其他内容。

您只需访问数据库一次即可完成此操作：

var tournaments = _db.TournamentBatchItems
                  // Where clause is optional, needed only if you have others locations than indoor and outdoor 
                 .Where(t => t.Location == "Outdoor" || t.Location == "Indoor")
                 .GroupBy(t => t.Location)
                 .Select(t => new { Name = $"{ t.Key } Tournaments", Value = t.Count()})
                 .ToList();

tournaments.Add(new { Name = "Total Tournaments", Value = tournaments.Sum(t => t.Value)});

---

您只需访问数据库一次即可完成此操作：

var tournaments = _db.TournamentBatchItems
                  // Where clause is optional, needed only if you have others locations than indoor and outdoor 
                 .Where(t => t.Location == "Outdoor" || t.Location == "Indoor")
                 .GroupBy(t => t.Location)
                 .Select(t => new { Name = $"{ t.Key } Tournaments", Value = t.Count()})
                 .ToList();

tournaments.Add(new { Name = "Total Tournaments", Value = tournaments.Sum(t => t.Value)});