关于DataTable的LINQ查询

使用LINQ来操作DataSet/DataTable中的数据

var results = from myRow in tblCurrentStock.AsEnumerable()
              where myRow.Field("item_name").ToUpper().StartsWith(tbSearchItem.Text.ToUpper())
              select myRow;
DataView view = results.AsDataView();

//Create DataTable 
DataTable dt= new DataTable();
dt.Columns.AddRange(New DataColumn[]
{
   new DataColumn("ID",typeOf(System.Int32)),
   new DataColumn("Name",typeOf(System.String))

});

//Fill with data

dt.Rows.Add(new Object[]{1,"Test1"});
dt.Rows.Add(new Object[]{2,"Test2"});

//Now  Query DataTable with linq
//To work with linq it should required our source implement IEnumerable interface.
//But DataTable not Implement IEnumerable interface
//So we call DataTable Extension method  i.e AsEnumerable() this will return EnumerableRowCollection


// Now Query DataTable to find Row whoes ID=1

DataRow drow = dt.AsEnumerable().Where(p=>p.Field(0)==1).FirstOrDefault();
 // 

试试这个简单的查询行:

var result=myDataTable.AsEnumerable().Where(myRow => myRow.Field("RowNo") == 1);

您可以在Rows集合上使用LINQ到对象,如下所示:

var results = from myRow in myDataTable.Rows where myRow.Field("RowNo") == 1 select myRow;

这是一个适合我并使用lambda表达式的简单方法:

var results = myDataTable.Select("").FirstOrDefault(x => (int)x["RowNo"] == 1)

然后,如果你想要一个特定的价值:

if(results != null) 
    var foo = results["ColName"].ToString()

试试这个

var row = (from result in dt.AsEnumerable().OrderBy( result => Guid.NewGuid()) select result).Take(3) ; 

最有可能的是,DataSet,DataTable和DataRow的类已在解决方案中定义.如果是这种情况,您将不需要DataSetExtensions参考.

防爆.DataSet类名 - > CustomSet,DataRow类名 - > CustomTableRow(具有已定义的列:RowNo,...)

var result = from myRow in myDataTable.Rows.OfType()
             where myRow.RowNo == 1
             select myRow;

或者(我更喜欢)

var result = myDataTable.Rows.OfType().Where(myRow => myRow.RowNo);

var results = from myRow in myDataTable
where results.Field("RowNo") == 1
select results;

在我的应用程序中,我发现在答案中建议使用LINQ to Datasets和DataTable的AsEnumerable()扩展非常慢.如果您对优化速度感兴趣,请使用James Newtonking的Json.Net库(http://james.newtonking.com/json/help/index.html)

// Serialize the DataTable to a json string
string serializedTable = JsonConvert.SerializeObject(myDataTable);    
Jarray dataRows = Jarray.Parse(serializedTable);

// Run the LINQ query
List results = (from row in dataRows
                    where (int) row["ans_key"] == 42
                    select row).ToList();

// If you need the results to be in a DataTable
string jsonResults = JsonConvert.SerializeObject(results);
DataTable resultsTable = JsonConvert.DeserializeObject(jsonResults);

关于如何实现此目的的示例如下:

DataSet dataSet = new DataSet(); //Create a dataset
dataSet = _DataEntryDataLayer.ReadResults(); //Call to the dataLayer to return the data

//LINQ query on a DataTable
var dataList = dataSet.Tables["DataTable"]
              .AsEnumerable()
              .Select(i => new
              {
                 ID = i["ID"],
                 Name = i["Name"]
               }).ToList();

对于VB.NET代码如下所示:

Dim results = From myRow In myDataTable  
Where myRow.Field(Of Int32)("RowNo") = 1 Select myRow

试试这个...

SqlCommand cmd = new SqlCommand( "Select * from Employee",con);
SqlDataReader dr = cmd.ExecuteReader( );
DataTable dt = new DataTable( "Employee" );
dt.Load( dr );
var Data = dt.AsEnumerable( );
var names = from emp in Data select emp.Field( dt.Columns[1] );
foreach( var name in names )
{
    Console.WriteLine( name );
}

IEnumerable result = from myRow in dataTableResult.AsEnumerable()
                             select myRow["server"].ToString() ;

你可以通过这样的linq让它变得优雅:

from prod in TenMostExpensiveProducts().Tables[0].AsEnumerable()
where prod.Field("UnitPrice") > 62.500M
select prod

或者像动态linq这样(AsDynamic直接在DataSet上调用):

TenMostExpensiveProducts().AsDynamic().Where (x => x.UnitPrice > 62.500M)

我更喜欢最后一种方法,而且最灵活.PS:别忘了连接System.Data.DataSetExtensions.dll参考

您可以尝试这样做，但是必须确保每个列的值类型

List result = myDataTable.AsEnumerable().Select(x=> new MyClass(){
     Property1 = (string)x.Field("ColumnName1"),
     Property2 = (int)x.Field("ColumnName2"),
     Property3 = (bool)x.Field("ColumnName3"),    
});