将此SQL与左连接转换为LINQ

Question

有两个表格，学校和学期。学校记录必须显示，但记录的词语可能尚不存在，因此，该词可能为空（即左连接）。如果存在，则必须按照当前术语的日期过滤左连接表。这可以在LINQ中完成吗？

select school.school_name, term.term_start, term.term_end 
from school 
left join term on school.school_id = term.school_id and term.term_start <= '2017-10-21' and term.term_end >= '2017-10-21' 
where school.active = 1 
order by school.school_name 

UPDATE：

一些输入后，我有一个左连接，但如果一所学校缺少一个学期，我仍然不能使开始和结束日期显示为空 - 学校不显示在所有如果我错过了一个学期，我想让学校在第一栏中展示。我在想什么？这是最新的LinqPad代码。

var query = ((from sc in Schools.Where(s => s.Active == 1) 
      join t in Terms on sc.School_id equals t.School_id into ts 
      from tsub in ts.DefaultIfEmpty() 
      select new {name = sc.School_name, 
         start = tsub.Term_start, 
         end = tsub.Term_end}) 
      .Where (o => o.start <= DateTime.Now && o.end >= DateTime.Now)) 
      .OrderBy(o => o.name); 

query.Dump(); 

更新＃2

下面是SQL结果的屏幕截图，我想实现在LINQ同样的事情：

Answer 1

我终于弄清楚了。如果将.Where（）子句放在连接的表上，如果没有匹配的记录，您将获得空值。这是LinqPad LINQ语句，它可以在.NET MVC中完美运行。

var query = ((from sc in Schools.Where(s => s.Active == 1) 
      join t in Terms.Where(x => x.Term_start <= DateTime.Now && x.Term_end >= DateTime.Now) on sc.School_id equals t.School_id into ts 
      from tsub in ts.DefaultIfEmpty() 
      select new {name = sc.School_name, 
         start = tsub.Term_start, 
         end = tsub.Term_end}) 
      .OrderBy(o => o.name)); 

query.Dump(); 

Answer 2

var query = from sc in school.Where(s = > s.active == 1) 
      join t in term on sc.school_id == t.school_id 
      select new {name = sc.school_name, 
         start = t.term_start, 
         end = term.term_end} 
      .Where (o => o.start <= '2017-10-21' && o.end >= '2017-10-21') 
      .OrderBy(o => o.school_name)