Question

当我检查空值时，我有一个Linq to SQL查询（在我看来）非常奇怪。

如上一个Linq所示，DB中有一条记录，但为什么前两个查询没有显示记录？

//Check
(record.SomeID == null ? "Yes" : "No"); //This prints Yes

//LINQ
var q = (from t in mySQLTable
         where t.PKID == record.PKID && 
         t.SomeID == record.SomeID
         select t).FirstOrDefault();
 //This prints nothing.  I.e. no records found

var q2 = (from t in mySQLTable
          where t.PKID == record.PKID &&
          t.SomeID == (record.SomeID == null ? null : record.SomeID)
          select t).FirstOrDefault();
 //This also prints nothing.  I.e. no records found

 var q3 = (from t in mySQLTable
           where t.PKID == record.PKID &&
           t.SomeID == null
           select t).FirstOrDefault();
 //This prints 1 record

Answer 1

您可以使用以下查询克服此问题：

bool isNull = record.SomeID == null;

var q = (from t in mySQLTable
         where t.PKID == record.PKID 
         && ( (isNull && t.SomeID == null)
             ||
              (!isNull && t.SomeID == record.SomeID)
            )
         select t).FirstOrDefault();

Linq to SQL检查null奇怪性

1 个答案: