LINQ Dataset（數據集）

數據集提供了一個非常有用的數據表示在存儲器中，用於數據的基礎應用的一個不同範圍。LINQ到數據集爲一個LINQ來執行查詢的數據集的數據無憂的方式ADO.NET工具的技術，並提高生產力。

LINQ到數據集的介紹

LINQ到數據集已取得查詢簡單的開發任務。它們並不需要在一個特定的查詢語言，可以用編程語言編寫相同的查詢。LINQ到數據集也是用於查詢，其中數據從多個數據源合併使用。這也並不需要任何LINQ提供程序從內存中集合訪問從LINQ 到 SQL和LINQ 到 XML讀取數據。

下面是其中一個數據源首先獲得，然後將數據集填充的兩個數據表一個LINQ到數據集的查詢的一個簡單的例子。關係是表和LINQ查詢被Join子句方式，對兩個表創建在兩者之間建立的。最後，foreach循環用於顯示所期望的結果。

C#

using System; using System.Collections.Generic; using System.Data; using System.Data.SqlClient; using System.Linq; using System.Text; using System.Threading.Tasks; namespace LINQtoDataset { class Program { static void Main(string[] args) { string connectString = System.Configuration.ConfigurationManager.ConnectionStrings["LinqToSQLDBConnectionString"].ToString(); string sqlSelect = "SELECT * FROM Department;" + "SELECT * FROM Employee;"; // Create the data adapter to retrieve data from the database SqlDataAdapter da = new SqlDataAdapter(sqlSelect, connectString); // Create table mappings da.TableMappings.Add("Table", "Department"); da.TableMappings.Add("Table1", "Employee"); // Create and fill the DataSet DataSet ds = new DataSet(); da.Fill(ds); DataRelation dr = ds.Relations.Add("FK_Employee_Department", ds.Tables["Department"].Columns["DepartmentId"], ds.Tables["Employee"].Columns["DepartmentId"]); DataTable department = ds.Tables["Department"]; DataTable employee = ds.Tables["Employee"]; var query = from d in department.AsEnumerable() join e in employee.AsEnumerable() on d.Field("DepartmentId") equals
e.Field("DepartmentId") select new { EmployeeId = e.Field("EmployeeId"), Name = e.Field("Name"), DepartmentId = d.Field("DepartmentId"), DepartmentName = d.Field("Name") }; foreach (var q in query) { Console.WriteLine("Employee Id = {0} , Name = {1} , Department Name = {2}", q.EmployeeId, q.Name, q.DepartmentName); } Console.WriteLine("\nPress any key to continue."); Console.ReadKey(); } } }

VB

Imports System.Data.SqlClient Imports System.Linq Module LinqToDataSet Sub Main() Dim connectString As String = System.Configuration.ConfigurationManager.ConnectionStrings("LinqToSQLDBConnectionString").ToString() Dim sqlSelect As String = "SELECT * FROM Department;" + "SELECT * FROM Employee;" Dim sqlCnn As SqlConnection = New SqlConnection(connectString) sqlCnn.Open() Dim da As New SqlDataAdapter da.SelectCommand = New SqlCommand(sqlSelect, sqlCnn) da.TableMappings.Add("Table", "Department") da.TableMappings.Add("Table1", "Employee") Dim ds As New DataSet() da.Fill(ds) Dim dr As DataRelation = ds.Relations.Add("FK_Employee_Department", ds.Tables("Department").Columns("DepartmentId"), ds.Tables("Employee").Columns("DepartmentId")) Dim department As DataTable = ds.Tables("Department") Dim employee As DataTable = ds.Tables("Employee") Dim query = From d In department.AsEnumerable() Join e In employee.AsEnumerable() On d.Field(Of Integer)("DepartmentId") Equals e.Field(Of Integer)("DepartmentId") Select New Person With{ _ .EmployeeId = e.Field(Of Integer)("EmployeeId"), .EmployeeName = e.Field(Of String)("Name"), .DepartmentId = d.Field(Of Integer)("DepartmentId"), .DepartmentName = d.Field(Of String)("Name") } For Each e In query Console.WriteLine("Employee Id = {0} , Name = {1} , Department Name = {2}", e.EmployeeId, e.EmployeeName, e.DepartmentName) Next Console.WriteLine(vbLf & "Press any key to continue.") Console.ReadKey() End Sub Class Person Public Property EmployeeId As Integer Public Property EmployeeName As String Public Property DepartmentId As Integer Public Property DepartmentName As String End Class End Module

當C#或VB的上述代碼被編譯和執行時，它產生了以下結果：

Employee Id = 1, Name = William, Department Name = Account
Employee Id = 2, Name = Benjamin, Department Name = Account
Employee Id = 3, Name = Miley, Department Name = Sales

Press any key to continue.

使用LINQ到數據集查詢數據集

在開始查詢使用LINQ到數據集數據集，這是至關重要的數據加載到數據集，這是通過或者使用DataAdapter類或LINQ到SQL完成的。使用LINQ到數據集查詢的提法和通過使用LINQ與其他LINQ使數據源制定查詢是非常相似的。

單表查詢

在下面的單表查詢，所有的在線訂單從SalesOrderHeaderTtable收集，然後命令ID，訂購日期和訂單號顯示爲輸出。

C#

using System; using System.Collections.Generic; using System.Data; using System.Data.SqlClient; using System.Linq; using System.Text; using System.Threading.Tasks; namespace LinqToDataset { class SingleTable { static void Main(string[] args) { string connectString = System.Configuration.ConfigurationManager.ConnectionStrings["LinqToSQLDBConnectionString"].ToString(); string sqlSelect = "SELECT * FROM Department;"; // Create the data adapter to retrieve data from the database SqlDataAdapter da = new SqlDataAdapter(sqlSelect, connectString); // Create table mappings da.TableMappings.Add("Table", "Department"); // Create and fill the DataSet DataSet ds = new DataSet(); da.Fill(ds); DataTable department = ds.Tables["Department"]; var query = from d in department.AsEnumerable() select new { DepartmentId = d.Field("DepartmentId"), DepartmentName = d.Field("Name") }; foreach (var q in query) { Console.WriteLine("Department Id = {0} , Name = {1}", q.DepartmentId, q.DepartmentName); } Console.WriteLine("\nPress any key to continue."); Console.ReadKey(); } } }

VB