Question

如何获取以下代码中的第一条记录？

subscription_end = (from ss in School_subs
                                .Where (s => s.School_id == sc.School_id) 
                                select ss.End_date)

以下是在LinqPad中使用的整个查询：

var query = ((from sc in Schools.Where(s => s.Active == 1)
                select new 
                        {
                        sc, 
                        teletardy_active = (from tt in Teletardies
                            .Where(t => t.School_id == sc.School_id) 
                            select tt.Active),
                        district_name = (from dd in Districts
                            .Where (d => d.District_id == sc.District_id) 
                            select dd.District_name),
                        subscription_end = (from ss in School_subs
                            .Where (s => s.School_id == sc.School_id) 
                            select ss.End_date)
                        }
                    ).OrderBy(o => o.sc.School_name));

query.Dump();

Answer 1

您可以使用First（），FirstOrDefault（）或Take（1）。如果您不确定是否至少有一个元素使用FirstOrDefault（），否则您可以使用First（）或Take（1）。但是take（1）将返回另一个包含单个元素的Enumerable，而不是单个元素本身。

subscription_end = (from ss in School_subs.Where (s => s.School_id == sc.School_id) select ss.End_date).FirstOrDefault();
if (subscription_end != null)
{
    // code to work with first elememnt
}

// Using first
subscription_end = (from ss in School_subs.Where (s => s.School_id == sc.School_id) select ss.End_date).First();

// Using take
(from ss in School_subs.Where (s => s.School_id == sc.School_id) select ss.End_date).Take(1);

Answer 2

MySQL不支持在MVC环境中由LINQ生成的复杂左连接和子查询。 LINQ可用于更简单的查询，但SQL应该用于那些更复杂的查询。

在LINQ左连接中获取第一条记录

2 个答案: