我正在尝试使用C#计算记录并使用Linq中的特定列对它们进行分组。
这是我要转换为Linq的SQL语句。我想将分组记录放到IEnumerable<object>
或List<object>
,以便我可以将列表传递给我的图表。
SELECT
G.[Description] AS Grade,
COUNT(CASE WHEN A.ApplicationStatusId = 1 THEN 1 END) AS Pending,
COUNT(CASE WHEN A.ApplicationStatusId = 2 THEN 1 END) AS Accepted,
COUNT(CASE WHEN A.ApplicationStatusId = 3 THEN 1 END) AS Rejected,
COUNT(ApplicationId) AS Total
FROM [Application] A
LEFT JOIN Grade G ON A.GradeId = G.GradeId
GROUP BY G.[Description]
这些是来自上述SQL语句的SQL结果。
我的课程
public class Application : Audit
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int ApplicationId { get; set; }
[DataType(DataType.DateTime)]
public DateTime? ApplicationDate { get; set; }
[StringLength(150)]
public string PreviousSchoolName { get; set; }
[StringLength(500)]
public string PreviousSchoolReportUrl { get; set; }
[StringLength(500)]
public string PreviousSchoolTransferUrl { get; set; }
public bool? Deleted { get; set; }
#region Foreign Keys
[ForeignKey("Leaner")]
public int? LeanerId { get; set; }
[ForeignKey("ApplicationStatus")]
public int? ApplicationStatusId { get; set; }
[ForeignKey("Grade")]
public int? GradeId { get; set; }
#endregion
#region Navigation Properties
public virtual Leaner Leaner { get; set; }
public virtual ApplicationStatus ApplicationStatus { get; set; }
public virtual Grade Grade { get; set; }
#endregion
public static Application GlobalApplication { get; set; }
public static IEnumerable<Grade> Grades { get; set; }
#region Dashboard Preperties - No Database Mapping
[NotMapped]
public int TotalApplications { get; set; }
[NotMapped]
public string GradeName { get; set; }
#endregion
}
public class Grade : LookupBase
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int GradeId { get; set; }
}
public abstract class LookupBase
{
[StringLength(50)]
public string Name { get; set; }
[StringLength(250)]
public string Description { get; set; }
}
public abstract class Audit
{
[DataType(DataType.DateTime)]
public DateTime? DateCreated { get; set; }
[DataType(DataType.DateTime)]
public DateTime? DateModified { get; set; }
public int? CreatedByOnlineUserId { get; set; }
public int? ModifiedByOnlineUserId { get; set; }
}
答案 0 :(得分:1)
当COUNT(expr)
不能expr
时(null
列就是这种情况),SQL聚合函数A.ApplicationStatusId
将映射到LINQ Count()
, Count(expr != null)
或Sum(expr != null ? 1 : 0)
否则(我更喜欢第二种,因为EF似乎可以更好地翻译)。
所以等效的LINQ查询可能是这样的:
var query =
from a in db.Application
group a by a.Grade.Description into g
select new
{
Grade = g.Key,
Pending = g.Sum(a => a.ApplicationStatusId == 1 ? 1 : 0),
Accepted = g.Sum(a => a.ApplicationStatusId == 2 ? 1 : 0),
Rejected = g.Sum(a => a.ApplicationStatusId == 3 ? 1 : 0),
Total = g.Count()
};