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;

1、投影

本主题中的示例演示如何使用 Select 和 SelectMany 方法通过使用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。

以下示例使用 Select 方法以将 Product.Name 和 Product.ProductID 属性投影到一系列匿名类型。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    var query = context.Products
        .Select(product => new
        {
            ProductId = product.ProductID,
            ProductName = product.Name
        });

    Console.WriteLine("Product Info:");
    foreach (var productInfo in query)
    {
        Console.WriteLine("Product Id: {0} Product name: {1} ",
            productInfo.ProductId, productInfo.ProductName);
    }
}

以下示例使用 Select 方法以只返回一系列产品名称。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    IQueryable<string> productNames = context.Products
        .Select(p => p.Name);

    Console.WriteLine("Product Names:");
    foreach (String productName in productNames)
    {
        Console.WriteLine(productName);
    }
}

以下示例使用 SelectMany 方法以选择 TotalDue 低于 500.00 的所有订单。

decimal totalDue = 500.00M;
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<Contact> contacts = context.Contacts;
    ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;

    var query =
    contacts.SelectMany(
        contact => orders.Where(order =>
            (contact.ContactID == order.Contact.ContactID)
                && order.TotalDue < totalDue)
            .Select(order => new
            {
                ContactID = contact.ContactID,
                LastName = contact.LastName,
                FirstName = contact.FirstName,
                OrderID = order.SalesOrderID,
                Total = order.TotalDue
            }));

    foreach (var smallOrder in query)
    {
        Console.WriteLine("Contact ID: {0} Name: {1}, {2} Order ID: {3} Total Due: ${4} ",
            smallOrder.ContactID, smallOrder.LastName, smallOrder.FirstName,
            smallOrder.OrderID, smallOrder.Total);
    }
}

以下示例使用 SelectMany 方法以选择在 2002 年 10 月 1 或此日期之后发出的所有订单。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<Contact> contacts = context.Contacts;
    ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;

    var query =
    contacts.SelectMany(
        contact => orders.Where(order =>
            (contact.ContactID == order.Contact.ContactID)
                && order.OrderDate >= new DateTime(2002, 10, 1))
            .Select(order => new
            {
                ContactID = contact.ContactID,
                LastName = contact.LastName,
                FirstName = contact.FirstName,
                OrderID = order.SalesOrderID,
                OrderDate = order.OrderDate
            }));

    foreach (var order in query)
    {
        Console.WriteLine("Contact ID: {0} Name: {1}, {2} Order ID: {3} Order date: {4:d} ",
            order.ContactID, order.LastName, order.FirstName,
            order.OrderID, order.OrderDate);
    }
}

2、筛选

本主题中的示例演示如何使用 Where 和 Where…Contains 方法，利用基于方法的查询语法来查询 AdventureWorks 销售模型。请注意，Where…Contains 不能用作已编译的查询的一部分。

这些示例中使用的 AdventureWorks 销售模型基于 AdventureWorks 示例数据库中的 Contact、Address、Product、SalesOrderHeader 和 SalesOrderDetail 等表生成。

以下示例返回所有联机订单。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    var onlineOrders = context.SalesOrderHeaders
        .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);
    }
}

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 = context.SalesOrderDetails
        .Where(order => order.OrderQty > orderQtyMin && order.OrderQty < orderQtyMax)
        .Select(s => new { s.SalesOrderID, s.OrderQty });

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

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 = AWEntities.Products.
        Where(p => productModelIds.Contains(p.ProductModelID));

    foreach (var product in products)
    {
        Console.WriteLine("{0}: {1}", product.ProductModelID, product.ProductID);
    }
}

3、排序

本主题中的示例演示如何使用 ThenBy 方法，通过基于方法的查询语法查询 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。

采用基于方法的查询语法的以下示例使用 OrderBy 和 ThenBy 以返回先按姓氏后按名字排序的联系人列表。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    IQueryable<Contact> sortedContacts = context.Contacts
        .OrderBy(c => c.LastName)
        .ThenBy(c => c.FirstName);

    Console.WriteLine("The list of contacts sorted by last name then by first name:");
    foreach (Contact sortedContact in sortedContacts)
    {
        Console.WriteLine(sortedContact.LastName + ", " + sortedContact.FirstName);
    }
}

以下示例使用 OrderBy 和 ThenByDescending 方法以首先按标价排序，然后执行产品名称的降序排序。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    IOrderedQueryable<Product> query = context.Products
        .OrderBy(product => product.ListPrice)
        .ThenByDescending(product => product.Name);

    foreach (Product product in query)
    {
        Console.WriteLine("Product ID: {0} Product Name: {1} List Price {2}",
            product.ProductID,
            product.Name,
            product.ListPrice);
    }
}

4、聚合计算

以下示例使用 Average 方法来查找产品的平均标价。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<Product> products = context.Products;

    Decimal averageListPrice =
        products.Average(product => product.ListPrice);

    Console.WriteLine("The average list price of all the products is ${0}",
        averageListPrice);
}

以下示例使用 Average 方法以查找每种样式的产品的平均标价。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<Product> products = context.Products;

    var query = from product in products
                group product by product.Style into g
                select new
                {
                    Style = g.Key,
                    AverageListPrice =
                        g.Average(product => product.ListPrice)
                };

    foreach (var product in query)
    {
        Console.WriteLine("Product style: {0} Average list price: {1}",
            product.Style, product.AverageListPrice);
    }
}

以下示例使用 Average 方法以查找平均应付款总计。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;

    Decimal averageTotalDue = orders.Average(order => order.TotalDue);
    Console.WriteLine("The average TotalDue is {0}.", averageTotalDue);
}

以下示例使用 Average 方法以获取每个联系人 ID 的平均应付款总计。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;

    var query =
        from order in orders
        group order by order.Contact.ContactID into g
        select new
        {
            Category = g.Key,
            averageTotalDue = g.Average(order => order.TotalDue)
        };

    foreach (var order in query)
    {
        Console.WriteLine("ContactID = {0} \t Average TotalDue = {1}",
            order.Category, order.averageTotalDue);
    }
}

以下示例使用 Average 方法以针对每个联系人获取具有平均应付款总计的订单。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;

    var query =
        from order in orders
        group order by order.Contact.ContactID into g
        let averageTotalDue = g.Average(order => order.TotalDue)
        select new
        {
            Category = g.Key,
            CheapestProducts =
                g.Where(order => order.TotalDue == averageTotalDue)
        };

    foreach (var orderGroup in query)
    {
        Console.WriteLine("ContactID: {0}", orderGroup.Category);
        foreach (var order in orderGroup.CheapestProducts)
        {
            Console.WriteLine("Average total due for SalesOrderID {1} is: {0}",
                order.TotalDue, order.SalesOrderID);
        }
        Console.Write("\n");
    }
}

以下示例使用 Count 方法以返回 Product 表中的产品数量。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<Product> products = context.Products;

    int numProducts = products.Count();

    Console.WriteLine("There are {0} products.", numProducts);
}

以下示例使用 Count 方法以返回联系人 ID 的列表和每个联系人 ID 所具有的订单数。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<Contact> contacts = context.Contacts;

    //Can't find field SalesOrderContact
    var query =
        from contact in contacts
        select new
        {
            CustomerID = contact.ContactID,
            OrderCount = contact.SalesOrderHeaders.Count()
        };

    foreach (var contact in query)
    {
        Console.WriteLine("CustomerID = {0} \t OrderCount = {1}",
            contact.CustomerID,
            contact.OrderCount);
    }
}

以下示例按颜色对产品进行分组，并使用 Count 方法以返回每个颜色组中的产品数量。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<Product> products = context.Products;

    var query =
        from product in products
        group product by product.Color into g
        select new { Color = g.Key, ProductCount = g.Count() };

    foreach (var product in query)
    {
        Console.WriteLine("Color = {0} \t ProductCount = {1}",
            product.Color,
            product.ProductCount);
    }
}

以下示例以长整型获取联系人计数。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<Contact> contacts = context.Contacts;

    long numberOfContacts = contacts.LongCount();
    Console.WriteLine("There are {0} Contacts", numberOfContacts);
}

以下示例使用 Max 方法以获取最大应付款总计。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;

    Decimal maxTotalDue = orders.Max(w => w.TotalDue);
    Console.WriteLine("The maximum TotalDue is {0}.",
        maxTotalDue);
}

以下示例使用 Max 方法以获取每个联系人 ID 的最大应付款总计。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;

    var query =
        from order in orders
        group order by order.Contact.ContactID into g
        select new
        {
            Category = g.Key,
            maxTotalDue =
                g.Max(order => order.TotalDue)
        };

    foreach (var order in query)
    {
        Console.WriteLine("ContactID = {0} \t Maximum TotalDue = {1}",
            order.Category, order.maxTotalDue);
    }
}

以下示例使用 Min 方法以获取每个联系人 ID 的最小应付款总计。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;

    var query =
        from order in orders
        group order by order.Contact.ContactID into g
        select new
        {
            Category = g.Key,
            smallestTotalDue =
                g.Min(order => order.TotalDue)
        };

    foreach (var order in query)
    {
        Console.WriteLine("ContactID = {0} \t Minimum TotalDue = {1}",
            order.Category, order.smallestTotalDue);
    }
}

以下示例使用 Sum 方法以获取每个联系人 ID 的应付款总计。

using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;

    var query =
        from order in orders
        group order by order.Contact.ContactID into g
        select new
        {
            Category = g.Key,
            TotalDue = g.Sum(order => order.TotalDue)
        };

    foreach (var order in query)
    {
        Console.WriteLine("ContactID = {0} \t TotalDue sum = {1}",
            order.Category, order.TotalDue);
    }
}

LINQ to Entities 查询一

`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;`

1、投影

2、筛选

3、排序

4、聚合计算

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