LINQ to DataSet的DataTable操作

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　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()           };

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