Question

我试图将我已编写的SQL查询转换为等效的Linq-To-Entities查询。它有一个子查询，将几个字段连接在一起，然后将其用作我需要加入的字段。

SQL：

select distinct ta.Filename
from TableA ta 
inner join ( 
    SELECT distinct isnull(tb.StringField,convert(varchar,tc.IntField) + convert(varchar,tb.IntFieldB)) as NewNames
        FROM TableB tb
        inner join TableC tc
            on tb.fkC = tc.ID
        ) tj
    on tj.NewNames = ta.Filename

这是我目前看到Linq查询的内容，但我知道它不正确。
LINQ：

var query = (from ta in ef.TableA
             where (from tb in ef.TableB
                    from tc in ef.TableC
                        .Where(tc => tc.ID == tb.fkC)
                    select new { NewNames = tb.StringField ?? SqlFunctions.StringConvert((double)tc.IntField) + SqlFunctions.StringConvert((double)tb.IntField2)}
                    ).Contains(ta.Filename)
             select ta.Filename
            ).Distinct().OrderBy(ta => ta.Filename).ToList();

由于子查询中创建的匿名类型，它抱怨Contains。这样做的正确方法是什么？

Answer 1

您可以尝试Any扩展方法：

var query = (from ta in ef.TableA
             where (from tb in ef.TableB
                    from tc in ef.TableC
                        .Where(tc => tc.ID == tb.fkC)
                    select new { NewNames = tb.StringField ?? SqlFunctions.StringConvert((double)tc.IntField) + SqlFunctions.StringConvert((double)tb.IntField2)}
                    ).Any(e.NewNames==ta.Filename)
             select ta.Filename
            ).Distinct().OrderBy(ta => ta.Filename).ToList();

或者您可以使用在连接操作后获得的字符串来预测内部查询：

var query = (from ta in ef.TableA
             where (from tb in ef.TableB
                    from tc in ef.TableC
                        .Where(tc => tc.ID == tb.fkC)
                    select  (tb.StringField ?? SqlFunctions.StringConvert((double)tc.IntField) + SqlFunctions.StringConvert((double)tb.IntField2))
                    ).Contains(ta.Filename)
             select ta.Filename
            ).Distinct().OrderBy(ta => ta.Filename).ToList();

更新

我认为以下内容可以改善您的查询：

var query = (from ta in ef.TableA
             where (from tb in ef.TableB
                    join tc in ef.TableC on tb.fkC equals tc.Id
                    where (tb.StringField ?? SqlFunctions.StringConvert((double)tc.IntField) + SqlFunctions.StringConvert((double)tb.IntField2))==ta.Filename
                    select tb).Any()
             select ta.Filename
            ).Distinct().OrderBy(ta => ta.Filename).ToList();

具有字符串连接的Linq-To-Entities子查询

1 个答案:

更新