Question

我有一个数据表。只有满足条件时，才需要使用常量和其他列的值填充列的值。

以下是针对SQL Server的。

UPDATE table SET ColumnA = 'MyValue.' + ID WHERE SOURCE IN ('1', '2')

如何在C＃中使用LINQ实现相同的目标？

我可以做这样的事情，但这将使我的where子句延伸。

var results = from myRow in table.AsEnumerable()
where myRow.Field<int>("SOURCE ") == 1 or myRow.Field<int>("SOURCE ") == 2
select myRow;

foreach (DataRow Row in results.Rows)
    Row["ColumnA"] = 'MyValue.' + Row["ID"] ;

Answer 1

您可以使用此Linq查询来更新数据表

List<int> lstSrc = new List<int> {1, 2};

table.AsEnumerable().Where(a => lstSrc.Contains(a.Field<int>("SOURCE")))
                    .Select(b => b["ColumnA"] = string.Concat("MyValue.", b["ID"]))
                    .ToList();

这将更新您的数据表列“ColumnA”

Answer 2

var results = from myRow in table.AsEnumerable()
where new List<int> {1, 2}.Contains(myRow.Field<int>("SOURCE "))
select myRow;

Answer 3

从概念上讲，这可以通过Join确保至少存在一个匹配来完成：

var query = from myRow in table.AsEnumerable()
    join source in sourceFilters
    on myRow.Field<int>("SOURCE") equals source
    into sources
    where sources.Any()
    select myRow;

Answer 4

我可以这样做：

public class YourObject
{
    public string Id {get;set;}
    public string Source {get;set;}
}

void Main()
{
    List<string> updateIds = new List<string>() {"1", "2"}; 

    List<YourObject> oldList = new List<YourObject>() 
    {
        new YourObject { Id = "1", Source = "test1" },
        new YourObject { Id = "2", Source = "test2" },
        new YourObject { Id = "3", Source = "test3" },
        new YourObject { Id = "4", Source = "test4" }
    };

    List<YourObject> newList = oldList.Where(i => updateIds.Contains(i.Id))
                                      .Select(j => {
                                                      j.Id="'MyValue.'" + j.Id; 
                                                      return j;
                                                   }).ToList();
}

Answer 5

1. dtNewLCM.AsEnumerable().Where(row => row.Field<string>("leafClass")=="0")
    .Select(b => b["leafClass"] = "MyValue1.")
    .ToList();

使用LINQ在In条件下更新数据表

5 个答案: