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在这里，我找到了如何使用 Linq2Sql 连接表并计算链接记录的数量LINQ - Left Join、Group By 和 Count

我已经实现了它，它对我来说没问题：以下表达式

var v = from c in db.GetTable<Country>()
        join t0 in db.GetTable<Team>() on c.Id equals t0.CountryId into t1
        from team in t1.DefaultIfEmpty()
        group team by c.Id into teamsGrouped
        select new CountryTeamsInfo
            {
                CountryId = teamsGrouped.Key,
                TeamsTotal = teamsGrouped.Count(),
                // TeamsWithoutOwnerFree = teamsGrouped.Count(t => t.OwnerId==0)
            }
            ;
         List<CountryTeamsInfo> res = v.ToList();

生成以下查询：

SELECT c.Id, Count(*) as c1
FROM countries c
LEFT JOIN teams t1 ON c.Id = t1.Country
GROUP BY c.Id

事实上，我还需要计算那些 OwnerId 字段不等于 0 的链接器记录。

看起来我应该在 linq 表达式 (TeamsWithoutOwnerFree = teamsGrouped.Count(t => t.OwnerId==0)) 中取消注释该行，但这不起作用，尝试执行会导致错误：

字典中不存在给定的键

查询不会出现在 SQL 日志文件中，我无法在调试器中检查它。

什么应该是从“团队”表中计算符合其他标准的行的正确方法。

PS 如果重要，我使用 C# 4.0、MySql 5.1 和 BLToolkit 4.1

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3 回答 3

1

也许尝试使用GroupJoin()您的查询：

var result = db.GetTable<Country>()
               .GroupJoin(db.GetTable<Team>(),
                   c => c.Id,
                   t => t.CountryId,
                   (country, teams) => new
                   {
                       CountryId = country.Id,
                       TeamsTotal = teams.Count(),
                       TeamsWithoutOwnerFree = teams.Count(t => t.OwnerId == 0)
                   })
               .ToList();
于 2012-04-18T11:01:37.333 回答
0

由于 RePierre 的帮助，我能够找到正确的查询：

var v = db.GetTable<Country>().Where(country => country.Allowed)
                    .GroupJoin(
                        db.GetTable<Team>(),
                        country => country.Id,
                        team => team.CountryId,
                        (country, teams) => new CountryTeamsInfo
                                                {
                                                    CountryId = country.Id,
                                                    TeamsTotal = teams.Count(),
                                                    TeamsWithoutOwnerFree = teams.Count(t => t.OwnerId != 0),
                                                }
                    ).GroupJoin(
                        db.GetTable<Team>().Where(te=>te.OwnerId==0),
                        cti => cti.CountryId,
                        team => team.CountryId,
                        (cti, teams) => new CountryTeamsInfo
                        {
                            CountryId = cti.CountryId,
                            TeamsTotal = cti.TeamsTotal,
                            TeamsWithoutOwnerFree = teams.Count(t => t.OwnerId != 0),
                        }
                    )
                    ;

我担心的是它使用了 2 个子查询......将尝试优化它。任何想法都会很棒

PS 实际上，生成的 SQL 查询看起来也很丑：

SELECT
cti.Id as Id1,
cti.c1 as c11,
(
    SELECT
        Count(*)
    FROM
        teams te
    WHERE
        cti.Id = te.Country AND te.User = 0
) as c2
FROM
(
    SELECT
        country.Id,
        (
            SELECT
                Count(*)
            FROM
                teams t1
            WHERE
                country.Id = t1.Country
        ) as c1
    FROM
        countries country
    WHERE
        country.allow
于 2012-04-19T13:24:56.410 回答
0

这是在我的环境中工作的查询：

from c in db.GetTable<Country>()
where c.Allowed
select new CountryTeamsInfo
{
    CountryId = c.Id,
    TeamsTotal = db.GetTable<Team>().Count(t => t.CountryId == c.Id && t.Allowed),
    TeamsHasOwner = db.GetTable<Team>().Count(t => t.CountryId == c.Id && t.Allowed && t.OwnerId != 0),
}

不是最好的解决方案（我需要在每个子查询中重复团队选择标准 t.Allowed），但仍然可以正常工作并且生成的 SQL 也很好。

于 2012-04-21T18:06:01.823 回答