查询表达式语法示例：筛选

项目
06/08/2023

本主题中的示例演示如何使用 Where 和 Where…Contains 方法以使用查询表达式语法来查询 AdventureWorks 销售模型。请注意，Where…Contains 不能用作编译的查询的一部分。

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：

using System;
using System.Data;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Objects;
using System.Globalization;
using System.Data.EntityClient;
using System.Data.SqlClient;
using System.Data.Common;


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

Where

示例

以下示例返回所有联机订单。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    var onlineOrders =
        from order in context.SalesOrderHeaders
        where order.OnlineOrderFlag == true
        select new
        {
            SalesOrderID = order.SalesOrderID,
            OrderDate = order.OrderDate,
            SalesOrderNumber = order.SalesOrderNumber
        };

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

Using context As New AdventureWorksEntities
    Dim orders As ObjectSet(Of SalesOrderHeader) = context.SalesOrderHeaders

    Dim onlineOrders = _
        From order In orders _
        Where order.OnlineOrderFlag = True _
        Select 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

示例

以下示例返回订单数量大于 2 且小于 6 的订单。

int orderQtyMin = 2;
int orderQtyMax = 6;
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    var query =
        from order in context.SalesOrderDetails
        where order.OrderQty > orderQtyMin && order.OrderQty < orderQtyMax
        select new
        {
            SalesOrderID = order.SalesOrderID,
            OrderQty = order.OrderQty
        };

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

Dim orderQtyMin = 2
Dim orderQtyMax = 6
Using context As New AdventureWorksEntities
    Dim orders As ObjectSet(Of SalesOrderDetail) = context.SalesOrderDetails

    Dim query = _
        From order In orders _
        Where order.OrderQty > orderQtyMin And order.OrderQty < orderQtyMax _
        Select 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

示例

以下示例返回所有红色产品。

String color = "Red";
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    var query =
        from product in context.Products
        where product.Color == color
        select new
        {
            Name = product.Name,
            ProductNumber = product.ProductNumber,
            ListPrice = product.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("");
    }
}

Dim color = "Red"
Using context As New AdventureWorksEntities
    Dim products As ObjectSet(Of Product) = context.Products

    Dim query = _
        From product In products _
        Where product.Color = color _
        Select 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

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 (AdventureWorksEntities context = new AdventureWorksEntities())
{
    IQueryable<SalesOrderHeader> query =
        from order in context.SalesOrderHeaders
        where order.OrderDate >= new DateTime(2003, 12, 1)
        select order;

    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.SalesOrderDetails)
        {
            Console.WriteLine("  Product ID: {0} Unit Price {1}",
                orderDetail.ProductID, orderDetail.UnitPrice);
        }
    }
}

Using context As New AdventureWorksEntities
    Dim orders As ObjectSet(Of SalesOrderHeader) = context.SalesOrderHeaders

    Dim query = _
        From order In orders _
        Where order.OrderDate >= New DateTime(2003, 12, 1) _
        Select 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.SalesOrderDetails
            Console.WriteLine("  Product ID: {0} Unit Price {1}", _
                orderDetail.ProductID, orderDetail.UnitPrice)
        Next
    Next
End Using

Where…Contains

示例

以下示例将一个数组用作 Where…Contains 子句的一部分，以查找 ProductModelID 与数组中的值匹配的所有产品。

using (AdventureWorksEntities AWEntities = new AdventureWorksEntities())
{
    int?[] productModelIds = {19, 26, 118};
    var products = from p in AWEntities.Products
                   where productModelIds.Contains(p.ProductModelID)
                   select p;
    foreach (var product in products)
    {
        Console.WriteLine("{0}: {1}", product.ProductModelID, product.ProductID);
    }
}

Using AWEntities As New AdventureWorksEntities()
    Dim productModelIds As System.Nullable(Of Integer)() = {19, 26, 118}
    Dim products = From p In AWEntities.Products _
                   Where productModelIds.Contains(p.ProductModelID) _
                   Select p
    For Each product In products
        Console.WriteLine("{0}: {1}", product.ProductModelID, product.ProductID)
    Next
End Using

备注

作为 Where…Contains 子句中谓词的一部分，您可以使用 Array、List<T> 或实现 IEnumerable<T> 接口的任何类型的集合。还可以在 LINQ to Entities 查询中声明和初始化集合。有关更多信息，请参见下一个示例。

示例

以下示例声明并初始化 Where…Contains 子句中的数组，以查找 ProductModelID 或 Size 与数组中的值匹配的所有产品。

using (AdventureWorksEntities AWEntities = new AdventureWorksEntities())
{
    var products = from p in AWEntities.Products
                   where (new int?[] { 19, 26, 18 }).Contains(p.ProductModelID) ||
                         (new string[] { "L", "XL" }).Contains(p.Size)
                   select p;
    foreach (var product in products)
    {
        Console.WriteLine("{0}: {1}, {2}", product.ProductID,
                                           product.ProductModelID,
                                           product.Size);
    }
}

Using AWEntities As New AdventureWorksEntities()
    Dim products = From p In AWEntities.Products _
                   Where (New System.Nullable(Of Integer)() {19, 26, 18}).Contains(p.ProductModelID) _
                   OrElse (New String() {"L", "XL"}).Contains(p.Size) _
                   Select p
    For Each product In products
        Console.WriteLine("{0}: {1}, {2}", product.ProductID, _
                                           product.ProductModelID, _
                                           product.Size)
    Next
End Using

请参阅

LINQ to Entities 中的查询

查询表达式语法示例：筛选

Where

示例

示例

示例

示例

Where…Contains

示例

示例

请参阅

其他资源