将简单的 Left Outer Join 和 group by SQL 语句转换为 Linq

Question

2 个表： 用户和警报

表：用户 用户 ID（整数）， 全名(varchar)

表格：警报 分配给（int）， 已解决（布尔）

查询：

SELECT u.Fullname, COUNT(resolved) as Assigned, SUM(CONVERT(int,Resolved)) as Resolved, COUNT(resolved) -  SUM(CONVERT(int,Resolved)) as Unresolved
FROM Alarm i LEFT OUTER JOIN Users u on i.AssignedTo = u.UserID
GROUP BY u.Fullname

结果：

Fullname  Assigned  Resolved  Unresolved
User1     204       4         200
User2     39        9         30
User3     235       200       35
User4     1         0         1
User5     469       69        400

对于我的生活，我无法弄清楚如何将它变成一个 Linq 查询。我在使用分组功能时遇到问题。 我看过无数的例子，没有一个例子有我的左外连接与分组的组合，或者它们太复杂了，我不知道如何让它与我的一起工作。这里的任何帮助将不胜感激！！！

更新： 我可能不清楚我在寻找什么。我正在寻找按用户 ID 的 AssignedTo 列分组的警报...除了，我想用位于 users 表中的 FullName 替换该用户 ID。有人发布并删除了一些接近的东西，除了它给了我用户表中的所有用户，这不是我想要的......

更新 2：在下面查看我的答案

Answer 1

假设你有以下模型：

这是警报的模型：

public class Alarm
{
    public int id { get; set; }

    public int AssignedTo { get; set; }

    [ForeignKey("AssignedTo")] 
    public virtual User User { get; set; }

    public bool Resolved { get; set; }
}

这是用户的模型：

public class User
{
    public int UserID { get; set; }

    public string FullName { get; set; }

    public virtual ICollection<Alarm> Alarms { get; set; }

    public User()
    {
        Alarms = new HashSet<Alarm>();
    }
}

这是为每个用户保存警报统计信息的模型：

public class UserStatistics
{
    public string FullName { get; set; }
    public int Assigned { get; set; }    
    public int Resolved { get; set; }    
    public int Unresolved { get; set; }    
}

然后您可以执行以下操作：

var query = context.Users.Select(
    user =>
        new UserStatistics
        {
            FullName = user.FullName,
            Assigned = user.Alarms.Count,
            Resolved = user.Alarms.Count(alarm => alarm.Resolved),
            Unresolved = user.Alarms.Count(alarm => !alarm.Resolved)
        });


var result = query.ToList();

对了，你也可以修改查询，去掉Unresolved = user.Alarms.Count(alarm => !alarm.Resolved)，然后把Unresolved属性变成这样的计算属性：

public class UserStatistics
{
    public string FullName { get; set; }
    public int Assigned { get; set; }    
    public int Resolved { get; set; }    
    public int Unresolved
    {
        get { return Assigned - Resolved; }
    }
}

这将使生成的 SQL 查询更简单。

Answer 2

我终于明白了。

这个：

var results = alarms.GroupBy(x => x.AssignedTo)
.Join(users, alm => alm.Key , usr => usr.UserID, (alm, usr) => new {
    Fullname = usr.FullName,AssignedNum = alm.Count(),
    Resolved = alm.Where(t=>t.resolved == true).Select(y => y.resolved).Count(), 
    Unresolved = alm.Where(t=>t.resolved == false).Select(y => y.resolved).Count() });

转载此：

SELECT u.Fullname, COUNT(resolved) as Assigned, SUM(CONVERT(int,Resolved)) as Resolved, 
       COUNT(resolved) -  SUM(CONVERT(int,Resolved)) as Unresolved
FROM Alarm i LEFT OUTER JOIN Users u on i.AssignedTo = u.UserID
GROUP BY u.Fullname

结果按 AssignedTo (int) 分组，但未选择 AssignedTo。而是从加入的用户表中选择 FullName。

非常感谢所有试图提供帮助的人！我从你的回答中学到了很多。

对于加分，我将如何用类似 SQL 的语法编写我的 lamdbda 答案？

Answer 3

试试这个：

from u in context.User
join a in context.Alarm on u.UserID equals a.AssignedTo into g1
from g2 in g1.DefaultIfEmpty()
group g2 by u.Fullname into grouped
select new { Fullname = grouped.Key, Assigned = grouped.Count(t=>t.Resolved != null), Resolved = grouped.Sum
                                    (t => int.Parse(t.Resolved)), Unresolved = (grouped.Count(t=>t.Resolved != null) - grouped.Sum
                                    (t => int.Parse(t.Resolved)))}

Answer 4

我猜在 Linq 中这个查询不一定要使用“Grouping”，因为“LEFT JOIN”+“GROUP BY”的组合将它们变成了“INNER JOIN”。

    var results =
        from u in users
        join a in alarms on u.UserID equals a.AssignedTo into ua
        select new
        {
            Fullname = u.FullName,
            Assigned = ua.Count(),
            Resolved = ua.Count(a => a.Resolved),
            Unresolved = ua.Count(a => !a.Resolved)
        };

        foreach (var r in results)
        {
            Console.WriteLine(r.Fullname + ", " + r.Assigned + ", " + r.Resolved + ", " + r.Unresolved);
        }