Question

是否可以将下面的linq查询合并到一个查询中？

var checkBoxes = from x in FindAll<CheckBox>()
                 where x.Checked
                 select new
                 {
                     RecordType = Type.GetType(x.Attributes["RecordType"]),
                     RecordId = Int32.Parse(x.Attributes["RecordId"])
                 };

checkBoxes = from x in checkBoxes
             where x.RecordType != typeof(DomainModel.Group)
             select x;

Answer 1

var checkBoxes = from x in FindAll<CheckBox>()
                 let recordType = Type.GetType(x.Attributes["RecordType"])
                 where x.Checked && recordType != typeof(DomainModel.Group)
                 select new
                 {
                     RecordType = recordType,
                     RecordId = Int32.Parse(x.Attributes["RecordId"])
                 };

Answer 2

lasseespeholt的答案非常好（最好，甚至 - 如果要丢掉结果，那么进行投影是没有意义的），但是如果你想更普遍地应用它，你可以使用查询继续：

var checkBoxes = from x in FindAll<CheckBox>()
                 where x.Checked
                 select new
                 {
                     RecordType = Type.GetType(x.Attributes["RecordType"]),
                     RecordId = Int32.Parse(x.Attributes["RecordId"])
                 } into y
                 where y.RecordType != typeof(DomainModel.Group)
                 select y;

我已将第二个变量从x更改为y，以明确它与原始x不同，但您不必这样做。< / p>

另一个避免调用Type.GetType两次但仍然在最终投影之前放置where子句的替代方法是使用let子句（无可否认地引入了另一个投影）：

var checkBoxes = from x in FindAll<CheckBox>()
                 where x.Checked
                 let t = Type.GetType(x.Attributes["RecordType]")
                 where t != typeof(DomainModel.Group)
                 select new
                 {
                     RecordType = t
                     RecordId = Int32.Parse(x.Attributes["RecordId"])
                 };

Answer 3

var checkboxes = FindAll<CheckBox>()
                  .Where(x => x.Checked && Type.GetType(x.Attributes["RecordType"]) != typeof(DomainModel.Group))
                  .Select(new{
                          RecordType = Type.GetType(x.Attributes["RecordType"]),
                          RecordId = Int32.Parse(x.Attributes["RecordId"])
                  });

Answer 4

为什么要更改为一个linq查询？ Linq使用延迟执行，只有在您实际使用输出时才会执行。在平均时间内不断构建表达式树。你拥有的是完全可读的。如果你认为它更具可读性，我只会改变它。

在linq查询中筛选所选的可枚举项

4 个答案: