Question

我有一个带有两列的数据表“tblFields”，它的值如下。

FieldId     FieldValue
-------     ----------
0_Name      test0
0_Amount    100
1_Name      test1
1_Amount    100
2_Name      test2
2_Amount    200
3_Name      test3
3_Amount    0.00
4_Name      test4
4_Amount

下面的linq为我提供了数据表中不以“0_”开头的所有行。现在我需要对此集合应用过滤器以获取金额（_Amount）不等于0.00或空的唯一行。此外，当_Amount等于0.00或为空时，它应该排除_Name行。

var pairs = from row in tblFields.AsEnumerable()
                        where !row.Field<string>("FieldId").StartsWith("0_")
                        select new
                        {
                            key = GetId(row.Field<string>("FieldId")),
                            value = row.Field<string>("FieldValue")
                        };

我正在寻找如下输出。是否有可能使用linq获得此结果？有没有人知道任何其他方法来实现这一目标？谢谢你的任何想法。

1_Name      test1
1_Amount    100
2_Name      test2
2_Amount    200

Answer 1

这应该有效（假设Field<T>方法返回类型T并且它适用于数字类型）：

var pairs = from row in tblFields.AsEnumerable()
            where !row.Field<string>("FieldId").StartsWith("0_")
            let value = row.Field<decimal>("FieldValue")
            where value != 0.00M
            select new
            {
                Id = row.Field<string>("FieldId"),
                Value = value
            }

如果Field<T>方法不适用于数字类型，请尝试以下操作：

var pairs = from row in tblFields.AsEnumerable()
            where !row.Field<string>("FieldId").StartsWith("0_")
            let fieldValueString  = row.Field<string>("FieldValue")
            let value = String.IsNullOrEmpty(fieldValueString)? 0M : Decimal.Parse(fieldValueString)
            where value != 0.00M
            select new
            {
                Id = row.Field<string>("FieldId"),
                Value = value
            }

这里应删除字段ID和值，但格式略有不同（但仍然很简单）：

var pair= from row in tblFields.AsEnumerable()
          group row by row.Field<string>("FieldId")[0] into idValueGroup
          where idValueGroup.Key != "0"
          select new
          {
              IdLine = idValueGroup.ElementAt(0),
              ValueLine = idValueGruop.ElementAt(1)
          } into linePair
          where linePair.ValueLine.Field<decimal>("FieldValue") != 0.00M
          select new
          {
              NameId = linePair.IdLine.Field<string>("FieldId"),
              Name = linePair.IdLine.Field<string>("FieldValue"),
              ValueId = linePair.ValueLine.Field<string>("FieldId"),
              Value = linePair.ValueLine.Field<decimal>("FieldValue")
          }

Answer 2

你可以这样做

var pairs = from row in tblFields.AsEnumerable()
                    where !row.Field<string>("FieldId").StartsWith("0_")
                    && row.Field<string>("FieldValue") != "0.00"
                    select new
                    {
                        key = GetId(row.Field<string>("FieldId")),
                        value = row.Field<string>("FieldValue")
                    };

测试代码

public class MyObject
{
    public string FieldId      { get; set; }
    public string FieldValue { get; set; }
}


List<MyObject> list = new List<MyObject> {
    new MyObject { FieldId = "0_Name", FieldValue = "test0"},
    new MyObject { FieldId = "1_Name", FieldValue = "test1" },
    new MyObject { FieldId = "2_Name", FieldValue = "test2" }
};

var pairs = from row in list
            where !row.FieldId.StartsWith("0_")
            && row.FieldValue != "0.00")
            select new
            {
                key = row.FieldId,
                value = row.FieldValue
            };

如何在一个可相关的集合上应用过滤器？

2 个答案:

测试代码