Sql 如何在LINQ中组合左JOIN、groupby和SUM？

我想用C#中的LINQ编写SQL查询

这是我的查询（对于每个组织，显示其Id、名称、主管、分析师和“收入”表中的收入总额）：

我已经试过这样的方法：

from o in Organization
join director in Employee on o.DirectorId equals director.Id into directorJoin
from d in directorJoin.DefaultIfEmpty()
join analyst in Employee on o.AnalystId equals analyst.Id into analystJoin
from a in analystJoin.DefaultIfEmpty()
join income in Income on o.Id equals income.OrganizationId into incomeJoin
group o by new 
{
    o.Id,
    o.Name,
    Director = d.FirstName + ' ' + d.LastName,
    Analyst = a.FirstName + ' ' + a.LastName,
    TotalIncome = (decimal?)incomeJoin.Sum(x => x.Amount)
} into g
  select g.Key

但我的程序给我带来了一个例外：

不支持嵌套查询。Operation1='GroupBy'Operation2='MultistreamTest'

---

我将非常感谢您的帮助。

您不想在组键内进行求和-在组外进行求和：

from o in Organization
join director in Employee on o.DirectorId equals director.Id into directorJoin
from d in directorJoin.DefaultIfEmpty()
join analyst in Employee on o.AnalystId equals analyst.Id into analystJoin
from a in analystJoin.DefaultIfEmpty()
join income in Income on o.Id equals income.OrganizationId into incomeJoin
group o by new 
{
    o.Id,
    o.Name,
    Director = d.FirstName + ' ' + d.LastName,
    Analyst = a.FirstName + ' ' + a.LastName,
    i.Amount
} into g
  select new 
{
    g.Key.Id,
    g.Key.Name,
    g.Key.Director,
    g.Key.Analyst,
    TotalIncome = (decimal?)g.Sum(i => i.Amount)
}

您可能还需要检查空值，因为您要加入到d、i和a中，我最终使用了建议的。以下是我的问题及其解决方案的简化版本：

型号：

public class Employee
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

public class Income
{
    public int Id { get; set; }
    public int OrganizationId { get; set; }
    public decimal Amount { get; set; }
}

public class Organization
{
    public int Id { get; set; }
    public string Name { get; set; }

    public int AnalystId { get; set; }
    public virtual Employee Analyst { get; set; }

    public int DirectorId { get; set; }
    public virtual Employee Director { get; set; }

    public virtual ICollection<Income> Incomes { get; set; }
}

---

我刚刚使用了您的查询，但没有得到任何语法错误。你能提供样本数据吗？不要加入。使用导航属性。如果你有像Organization.Incomes这样的东西，这个问题就变得非常简单了。顺便说一句，该错误是由分组表达式中的聚合语句引起的。就像在SQL中一样，它不属于那里。@SurajKumar没有语法错误，但是在实体框架执行期间引发了异常。@GertArnold感谢我使用了导航属性。我只是好奇使用这种方法是否有任何性能问题。导航属性转换为SQL中的

JOIN

语句，因此它们的性能不应该比手动JOIN语句差。很好，我不知道这一点。修正了我的答案。再次感谢

public class Employee
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

public class Income
{
    public int Id { get; set; }
    public int OrganizationId { get; set; }
    public decimal Amount { get; set; }
}

public class Organization
{
    public int Id { get; set; }
    public string Name { get; set; }

    public int AnalystId { get; set; }
    public virtual Employee Analyst { get; set; }

    public int DirectorId { get; set; }
    public virtual Employee Director { get; set; }

    public virtual ICollection<Income> Incomes { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        var context = new Context();

        var queryResult = context.Organizations.Select(x => new
        {
            x.Id,
            x.Name,
            Director = x.Director.FirstName + " " + x.Director.LastName,
            Analyst = x.Analyst.FirstName + " " + x.Analyst.LastName,
            TotalIncome = x.Incomes.Sum(y => y.Amount)
        });

    }
}