基于方法的查询语法示例：限制 (LINQ to Entities)

本主题中的示例演示如何使用 Where 方法通过基于方法的查询语法以查询 AdventureWorks 销售模型。这些示例中使用的 AdventureWorks 销售模型从 AdventureWorks 示例数据库中的 Contact、Address、Product、SalesOrderHeader 和 SalesOrderDetail 等表生成。

本主题中的示例使用下面的 using/Imports 语句：

Option Explicit On
Option Strict On
Imports L2EExamplesVB.AdventureWorksModel
Imports System.Data.Objects
Imports System.Globalization

using System;
using System.Data;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Objects;
using AdventureWorksModel;
using System.Globalization;

有关更多信息，请参见如何：在 Visual Studio 中创建 LINQ to Entities 项目。

Where

示例

以下示例返回所有联机订单。

Using AWEntities As New AdventureWorksEntities
    Dim onlineOrders = AWEntities.SalesOrderHeader _
        .Where(Function(order) order.OnlineOrderFlag = True) _
        .Select(Function(order) New With { _
           .SalesOrderID = order.SalesOrderID, _
           .OrderDate = order.OrderDate, _
           .SalesOrderNumber = order.SalesOrderNumber _
        })

    For Each onlineOrder In onlineOrders
        Console.WriteLine("Order ID: {0} Order date: {1:d} Order number: {2}", _
                onlineOrder.SalesOrderID, _
                onlineOrder.OrderDate, _
                onlineOrder.SalesOrderNumber)
    Next
End Using

using (AdventureWorksEntities AWEntities = new AdventureWorksEntities())
{
    var onlineOrders = AWEntities.SalesOrderHeader
        .Where(order => order.OnlineOrderFlag == true)
        .Select(s => new { s.SalesOrderID, s.OrderDate, s.SalesOrderNumber });

    foreach (var onlineOrder in onlineOrders)
    {
        Console.WriteLine("Order ID: {0} Order date: {1:d} Order number: {2}",
            onlineOrder.SalesOrderID,
            onlineOrder.OrderDate,
            onlineOrder.SalesOrderNumber);
    }
}

示例

以下示例返回订单数量大于 2 且小于 6 的订单。

Using AWEntities As New AdventureWorksEntities
    Dim query = AWEntities.SalesOrderDetail _
        .Where(Function(order) order.OrderQty > 2 And order.OrderQty < 6) _
        .Select(Function(order) New With { _
            .SalesOrderID = order.SalesOrderID, _
            .OrderQty = order.OrderQty _
        })

    For Each order In query
        Console.WriteLine("Order ID: {0} Order quantity: {1}", _
                order.SalesOrderID, order.OrderQty)
    Next
End Using

using (AdventureWorksEntities AWEntities = new AdventureWorksEntities())
{
    var query = AWEntities.SalesOrderDetail
        .Where(order => order.OrderQty > 2 && order.OrderQty < 6)
        .Select(s => new { s.SalesOrderID, s.OrderQty });

    foreach (var order in query)
    {
        Console.WriteLine("Order ID: {0} Order quantity: {1}",
            order.SalesOrderID, order.OrderQty);
    }
}

示例

以下示例返回所有红色产品。

Using AWEntities As New AdventureWorksEntities
    Dim query = AWEntities.Product _
        .Where(Function(product) product.Color = "Red") _
        .Select(Function(product) New With { _
            .Name = product.Name, _
            .ProductNumber = product.ProductNumber, _
            .ListPrice = product.ListPrice _
        })

    For Each product In query
        Console.WriteLine("Name: {0}", product.Name)
        Console.WriteLine("Product number: {0}", product.ProductNumber)
        Console.WriteLine("List price: ${0}", product.ListPrice)
        Console.WriteLine("")
    Next
End Using

using (AdventureWorksEntities AWEntities = new AdventureWorksEntities())
{
    var query = AWEntities.Product
        .Where(product => product.Color == "Red")
        .Select(p => new { p.Name, p.ProductNumber, p.ListPrice });

    foreach (var product in query)
    {
        Console.WriteLine("Name: {0}", product.Name);
        Console.WriteLine("Product number: {0}", product.ProductNumber);
        Console.WriteLine("List price: ${0}", product.ListPrice);
        Console.WriteLine("");
    }
}

示例

以下示例使用 Where 方法以查找在 2003 年 12 月 1 日之后生成的订单，然后使用 order.SalesOrderDetail 导航属性以获取每个订单的详细信息。

Using AWEntities As New AdventureWorksEntities
    Dim query = AWEntities.SalesOrderHeader _
        .Where(Function(order) order.OrderDate >= New DateTime(2003, 12, 1)) _
        .Select(Function(order) order)

    Console.WriteLine("Orders that were made after December 1, 2003:")
    For Each order In query
        Console.WriteLine("OrderID {0} Order date: {1:d} ", _
                order.SalesOrderID, order.OrderDate)
        For Each orderDetail In order.SalesOrderDetail
            Console.WriteLine("  Product ID: {0} Unit Price {1}", _
                orderDetail.ProductID, orderDetail.UnitPrice)
        Next
    Next
End Using

using (AdventureWorksEntities AWEntities = new AdventureWorksEntities())
{
    IQueryable<SalesOrderHeader> query = AWEntities.SalesOrderHeader
        .Where(order => order.OrderDate >= new DateTime(2003, 12, 1))
        .Select(o => o);

    Console.WriteLine("Orders that were made after December 1, 2003:");
    foreach (SalesOrderHeader order in query)
    {
        Console.WriteLine("OrderID {0} Order date: {1:d} ",
            order.SalesOrderID, order.OrderDate);
        foreach (SalesOrderDetail orderDetail in order.SalesOrderDetail)
        {
            Console.WriteLine("  Product ID: {0} Unit Price {1}",
                orderDetail.ProductID, orderDetail.UnitPrice);
        }
    }
}

另请参见

概念

基于方法的查询语法示例 (LINQ to Entities)