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数据集特定的运算符示例 (LINQ to DataSet)

  • 项目

本主题中的示例演示如何使用 CopyToDataTable 方法和 DataRowComparer 类。

这些示例中使用的 FillDataSet 方法在将数据加载到数据集中中指定。

本主题中的示例使用 AdventureWorks 示例数据库中的 Contact、Address、Product、SalesOrderHeader 和 SalesOrderDetail 表。

本主题中的示例使用下面的 using/Imports 语句：

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Globalization;
using System.Linq;
using System.Windows.Forms;

Option Explicit On

Imports System.Linq
Imports System.Linq.Expressions
Imports System.Collections.Generic
Imports System.Data
Imports System.Data.SqlClient
Imports System.Data.Common
Imports System.Globalization

有关详细信息，请参阅如何：在 Visual Studio 中创建 LINQ to DataSet 项目。

CopyToDataTable

示例

此示例通过使用 DataTable 方法加载包含查询结果的 CopyToDataTable。

// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);

DataTable contacts1 = ds.Tables["Contact"];

IEnumerable<DataRow> query =
    from contact in contacts1.AsEnumerable()
    where contact.Field<string>("Title") == "Ms."
        && contact.Field<string>("FirstName") == "Carla"
    select contact;

DataTable contacts2 = query.CopyToDataTable();

foreach (DataRow contact in contacts2.AsEnumerable())
{
    Console.WriteLine("ID:{0} Name: {1}, {2}",
        contact.Field<Int32>("ContactID"),
        contact.Field<string>("LastName"),
        contact.Field<string>("FirstName"));
}

' Fill the DataSet.
Dim ds As New DataSet()
ds.Locale = CultureInfo.InvariantCulture
' See the FillDataSet method in the Loading Data Into a DataSet topic.
FillDataSet(ds)

Dim contactTable As DataTable = ds.Tables("Contact")

Dim query = _
    From contact In contactTable.AsEnumerable() _
    Where contact.Field(Of String)("Title") = "Ms." _
            And contact.Field(Of String)("FirstName") = "Carla" _
    Select contact

Dim contacts = query.CopyToDataTable().AsEnumerable()

For Each contact In contacts
    Console.Write("ID: " & contact.Field(Of Integer)("ContactID"))
    Console.WriteLine(" Name: " & contact.Field(Of String)("LastName") & _
                      ", " & contact.Field(Of String)("FirstName"))
Next

DataRowComparer

示例

此示例通过使用 DataRowComparer 比较两个不同的数据行。

// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);

// Get two rows from the SalesOrderHeader table.
DataTable table = ds.Tables["SalesOrderHeader"];
DataRow left = (DataRow)table.Rows[0];
DataRow right = (DataRow)table.Rows[1];

// Compare the two different rows.
IEqualityComparer<DataRow> comparer = DataRowComparer.Default;

bool bEqual = comparer.Equals(left, right);
if (bEqual)
    Console.WriteLine("The two rows are equal");
else
    Console.WriteLine("The two rows are not equal");

// Get the hash codes of the two rows.
Console.WriteLine("The hashcodes for the two rows are {0}, {1}",
    comparer.GetHashCode(left),
    comparer.GetHashCode(right));

请参阅