Csharp 为什么EF Core 6会针对null验证Count(*)

我有以下简单的查询:

var students = from s in dbContext.Students
               select new 
                      {
                          Name = s.Name,
                          HasGrades = s.Grades.Where(x => x.IsActive).Count() == 1
                      };

列HasGrades是布尔值，只有当学生正好存在一个活动分数时，才必须显示为true.

我有点困惑为什么EF Core将其翻译成两个子查询，并额外判断COUNT(*)个结果与null？Postgr COUNT(*)永远不会返回null:

SELECT 
    s."NAME" AS "Name", 
    ((SELECT COUNT(*)::INT
      FROM "GRADES" AS p0
      WHERE (s."NAME" = p0."NAME") AND p0."IS_ACTIVE") = 1) 
        AND (((SELECT COUNT(*)::INT
               FROM "GRADES" AS p0
               WHERE (s."NAME" = p0."NAME") AND p0."IS_ACTIVE") IS NOT NULL)) AS "HasGrades"
FROM 
    "STUDENTS" AS s

最新情况:

如果我改变这条线

HasGrades = s.Grades.Where(x => x.IsActive).Count() == 1

对此:

HasGrades = s.Grades.Where(x => x.IsActive).Count() == 1 ? true : false

那么它就被翻译成

 CASE
    WHEN (
        SELECT COUNT(*)::INT
        FROM "GRADES" AS p1
        WHERE (p."NAME" = p1."NAME") AND p1."IS_ACTIVE") = 1 THEN TRUE
    ELSE FALSE
END

看起来这是一个更好的结果