LINQ to DataSet需要使用System.Core.dll、System.Data.dll和System.Data.DataSetExtensions.dll，在项目中添加引用System.Data和System.Data.DataSetExtensions。
1. DataTable读取列表
DataSet ds = new DataSet();
// 省略ds的Fill代码
DataTable products = ds.Tables["Product"];
IEnumerable<DataRow> rows = from p in products.AsEnumerable()
select p;
foreach (DataRow row in rows)
{
Console.WriteLine(row.Field<string>("ProductName"));
}
DataSet ds = new DataSet();
// 省略ds的Fill代码
DataTable products = ds.Tables["Product"];
var rows = products.AsEnumerable()
.Select(p => new
{
ProductID = p.Field<int>("ProductID"),
ProductName = p.Field<string>("ProductName"),
UnitPrice = p.Field<decimal>("UnitPrice")
});
foreach (var row in rows)
{
Console.WriteLine(row.ProductName);
}
var products = ds.Tables["Product"].AsEnumerable();
var query = from p in products
select p.Field<string>("ProductName");
2. DataTable查询
var rows = products.AsEnumerable()
.Where(p => p.Field<decimal>("UnitPrice") > 10m)
.Select(p => new
{
ProductID = p.Field<int>("ProductID"),
ProductName = p.Field<string>("ProductName"),
UnitPrice = p.Field<decimal>("UnitPrice")
});
3. DataTable数据排序
var rows = products.AsEnumerable()
.Where(p => p.Field<decimal>("UnitPrice") > 10m)
.OrderBy(p => p.Field<int>("SortOrder"))
.Select(p => new
{
ProductID = p.Field<int>("ProductID"),
ProductName = p.Field<string>("ProductName"),
UnitPrice = p.Field<decimal>("UnitPrice")
});
var expr = from p in products.AsEnumerable()
orderby p.Field<int>("SortOrder")
select p;
IEnumerable<DataRow> rows = expr.ToArray();
foreach (var row in rows)
{
Console.WriteLine(row.Field<string>("ProductName"));
}
var expr = from p in ds.Tables["Product"].AsEnumerable()
orderby p.Field<int>("SortOrder"), p.Field<string>("ProductName") descending
select p;
4. 多个DataTable查询
var query = from p in ds.Tables["Product"].AsEnumerable()
from c in ds.Tables["Category"].AsEnumerable()
where p.Field<int>("CategoryID") == c.Field<int>("CategoryID")
&& p.Field<decimal>("UnitPrice") > 10m
select new
{
ProductID = p.Field<int>("ProductID"),
ProductName = p.Field<string>("ProductName"),
CategoryName = c.Field<string>("CategoryName")
};
5. DataTable分组
var query = from p in ds.Tables["Product"].AsEnumerable()
group p by p.Field<int>("CategoryID") into g
select new
{
CategoryID = g.Key,
Products = g
};
foreach (var item in query)
{
Console.WriteLine(item.CategoryID);
foreach (var p in item.Products)
{
Console.WriteLine(p.Field<string>("ProductName"));
}
}
查询Product中每个CategoryID的数目：
var expr = from p in ds.Tables["Product"].AsEnumerable()
group p by p.Field<int>("CategoryID") into g
select new
{
CategoryID = g.Key,
ProductsCount = g.Count()
};
DataTable与Linq相互转换
DataTable通过dt.AsEnumerable()方法转换可用Linq查询，反之，Linq也可以转化为DataTable
DataTable newDt = query1.CopyToDataTable<DataRow>();
var query1 =
from stu in dtStu.AsEnumerable()
from score in dtScore.AsEnumerable()
where stu.Field<int>("ScoreID") == score.Field<int>("ScoreID")
where (int)stu["Age"] > 20
select stu;
//通过CopyToDataTable()方法创建新的副本
DataTable newDt = query1.CopyToDataTable<DataRow>();
foreach (var item in newDt.AsEnumerable())
{
System.Console.WriteLine(item["Name"]);
}
