第二篇 Entity Framework Plus 之 Query Future

从性能的角度出发，能够减少增，删，改，查，跟数据库打交道次数，肯定是对性能会有所提升的（这里单纯是数据库部分）。

今天主要怎样减少Entity Framework查询跟数据库打交道的次数，来提高查询性能。

举一个大家最常用功能 “分页” 功能。先贴一段代码。

       private static IEnumerable<OrderModel> FindPagerOrders(int pageSize, int pageIndex, out int totalCount)
        {
            using (var dbContext = new EntityFrameworkPlusDbContext())
            {
                var orders = dbContext.Orders.OrderBy(o => o.CreateDateTime);

                totalCount  = orders.Count();

                var pagerOrders = orders.Skip((pageIndex - 1) * pageSize).Take(pageSize);

                return pagerOrders .ToList();
            }
        }

这类型的代码，大家估计都看到过，也自己写过，简单分析一下。

orders.Count() 返回int 类型，肯定要查询出数据库才知道订单总笔数。

pagerOrders.ToList() 返回 IEnumerable<T> 类型，这个不用解释Entity Framework IEnumerable 和 IQueryable 区别是

IEnumerable 会执行SQL，IQueryable 而不会。所以这句也会去数据库查询一次。

那整个分页功能用Entity Framework 就是最少要两次数据库查询，刚刚上面说了，一个基本的提高性能方法就要减少与数据库打交道次数。

从“分页”功能来说，要是变成只有一次与数据库打交道，那就是对性能有大提升。Entity Framework 自身是没有提供这样的方法。

Entity Framework Plus 库 Query Future 扩展，是一个对Entity Framework 功能的延伸和扩展，能够做到减少数据库打交道次数。使查询性能更高。

一 . Entity Framework Plus 库 Query Future 安装

1. 解决方案还是我上一篇第一篇 Entity Framework Plus 之 Audit 用的解决方案“EntityFrameworkPlusSolution”，新增 “EntityFrameworkPlus.QueryFuture.Demo” 控制台项目，作为Entity Framework Plus 库 Query Future 扩展应用和展示功能项目。项目结构截图如下

项目关系图（代码图）

2. 为了方便Demo，新增商品业务相关的 Model，Mapping，以及改动DbContext 如下代码

GoodsModel

using System;

namespace EntityFrameworkPlus.Models
{
    public class GoodsModel
    {
        public System.Guid GoodsGuid { get; set; }
        public string GoodsNo { get; set; }
        public string GoodsName { get; set; }
        public string GoodsBrand { get; set; }
        public decimal UnitPrice { get; set; }
        public string Description { get; set; }
        public string Creator { get; set; }
        public System.DateTime CreateDateTime { get; set; }
        public string LastModifier { get; set; }
        public DateTime? LastModifiedDateTime { get; set; } 
    }
}

GoodsMap

using System.Data.Entity.ModelConfiguration;
using EntityFrameworkPlus.Models;

namespace EntityFrameworkPlus.Mappings
{
    public class GoodsMap: EntityTypeConfiguration<GoodsModel>
    {
        public GoodsMap()
        {
            // Primary Key
            this.HasKey(t => t.GoodsGuid);

            // Properties
            this.Property(t => t.GoodsNo)
                .IsRequired()
                .HasMaxLength(50);

            this.Property(t => t.GoodsName)
                .IsRequired()
                .HasMaxLength(50);

            this.Property(t => t.GoodsBrand)
                .IsRequired()
                .HasMaxLength(50);

            this.Property(t => t.Creator)
                .IsRequired()
                .HasMaxLength(20);

            this.Property(t => t.LastModifier)
                .HasMaxLength(20);

            // Table & Column Mappings
            this.ToTable("Sample_Goods");
            this.Property(t => t.GoodsGuid).HasColumnName("GoodsGuid");
            this.Property(t => t.GoodsNo).HasColumnName("GoodsNo");
            this.Property(t => t.GoodsName).HasColumnName("GoodsName");
            this.Property(t => t.GoodsBrand).HasColumnName("GoodsBrand");
            this.Property(t => t.UnitPrice).HasColumnName("UnitPrice");
            this.Property(t => t.Description).HasColumnName("Description");
            this.Property(t => t.Creator).HasColumnName("Creator");
            this.Property(t => t.CreateDateTime).HasColumnName("CreateDateTime");
            this.Property(t => t.LastModifier).HasColumnName("LastModifier");
            this.Property(t => t.LastModifiedDateTime).HasColumnName("LastModifiedDateTime");
        }
    }
}

EntityFrameworkPlusDbContext

using System.Data.Entity;
using EntityFrameworkPlus.Mappings;
using EntityFrameworkPlus.Models;
using Z.EntityFramework.Plus;

namespace EntityFrameworkPlus.DbContext
{
    public class EntityFrameworkPlusDbContext : System.Data.Entity.DbContext
    {
        public EntityFrameworkPlusDbContext()
            : base("EntityFrameworkPlusConnection")
        {
        }
        public DbSet<AuditEntry> AuditEntries { get; set; }
        public DbSet<AuditEntryProperty> AuditEntryProperties { get; set; }
        public DbSet<OrderModel> Orders { get; set; }
        public DbSet<GoodsModel> Goodses { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {

            modelBuilder.Configurations.Add(new OrderMap());
            modelBuilder.Configurations.Add(new GoodsMap());

            base.OnModelCreating(modelBuilder);
        }

    }
}

3. 右键 “EntityFrameworkPlus.QueryFuture.Demo” 项目，选择“管理NuGet程序包”，关联部分右上角搜索“Z.EntityFramework.Plus” ，然后选择 “EntityFramework Plus (EF6) | Query Deferred”&“EntityFramework Plus (EF6) | Query Futurn” 两项安装

二. Entity Framework Plus 库 Query Future 扩展功能实作

1. 在 “EntityFrameworkPlus.QueryFuture.Demo” 项目 Program 新增3个静态方法，分别是

FindOrdersWithGoodsies() 查询订单信息和商品信息

FindPagerOrders(int pageSize, int pageIndex, out int totalCount) 订单分页查询

FindGoodsMaxWithMinUnitPrice() 查询单价最大和最小的商品

详细代码如下

using System.Collections.Generic;
using System.Linq;
using EntityFrameworkPlus.DbContext;
using EntityFrameworkPlus.Models;
using Z.EntityFramework.Plus;

namespace EntityFrameworkPlus.QueryFuture.Demo
{
    class Program
    {
        static void Main(string[] args)
        {
            //1.查询订单信息和商品信息
            FindOrdersWithGoodsies();

            //2. 订单分页查询
            //var totalCount = 0;
            //FindPagerOrders(10, 1, out totalCount);

            //3.查询单价最大和最小的商品
            //FindGoodsMaxWithMinUnitPrice();
        }

        private static void FindOrdersWithGoodsies()
        {
            using (var dbContext = new EntityFrameworkPlusDbContext())
            {
                var futureOrders = dbContext.Orders.Future();
                var futureGoodsies = dbContext.Goodses.Future();
                var orders = futureOrders.ToList();
                var goodsies = futureGoodsies.ToList();
            }
        }

        private static IEnumerable<OrderModel> FindPagerOrders(int pageSize, int pageIndex, out int totalCount)
        {
            using (var dbContext = new EntityFrameworkPlusDbContext())
            {
                var orders = dbContext.Orders.OrderBy(o => o.CreateDateTime);

                var futureCount = orders.DeferredCount().FutureValue();

                var futurePagerOrders = orders.Skip((pageIndex - 1) * pageSize).Take(pageSize).Future();

                totalCount = futureCount.Value;

                return futurePagerOrders.ToList();
            }
        }

        private static void FindGoodsMaxWithMinUnitPrice()
        {
            using (var dbContext = new EntityFrameworkPlusDbContext())
            {
                var futureMaxGoodsUnitPrice = dbContext.Goodses.DeferredMax(g => g.UnitPrice).FutureValue<decimal>();
                var futureMinGoodsUnitPrice = dbContext.Goodses.DeferredMin(g => g.UnitPrice).FutureValue<decimal>();
                var maxGoodsUnitPrice = futureMaxGoodsUnitPrice.Value;
                var minGoodsUnitPrice = futureMaxGoodsUnitPrice.Value;
            }
        }

    }
}

2. 3个方法的SQL追踪和截图

FindOrdersWithGoodsies

-- EF+ Query Future: 1 of 2
SELECT 
    [Extent1].[OrderGuid] AS [OrderGuid], 
    [Extent1].[OrderNo] AS [OrderNo], 
    [Extent1].[OrderCreator] AS [OrderCreator], 
    [Extent1].[OrderDateTime] AS [OrderDateTime], 
    [Extent1].[OrderStatus] AS [OrderStatus], 
    [Extent1].[Description] AS [Description], 
    [Extent1].[Creator] AS [Creator], 
    [Extent1].[CreateDateTime] AS [CreateDateTime], 
    [Extent1].[LastModifier] AS [LastModifier], 
    [Extent1].[LastModifiedDateTime] AS [LastModifiedDateTime]
    FROM [dbo].[Sample_Order] AS [Extent1]


-- EF+ Query Future: 2 of 2
SELECT 
    [Extent1].[GoodsGuid] AS [GoodsGuid], 
    [Extent1].[GoodsNo] AS [GoodsNo], 
    [Extent1].[GoodsName] AS [GoodsName], 
    [Extent1].[GoodsBrand] AS [GoodsBrand], 
    [Extent1].[UnitPrice] AS [UnitPrice], 
    [Extent1].[Description] AS [Description], 
    [Extent1].[Creator] AS [Creator], 
    [Extent1].[CreateDateTime] AS [CreateDateTime], 
    [Extent1].[LastModifier] AS [LastModifier], 
    [Extent1].[LastModifiedDateTime] AS [LastModifiedDateTime]
    FROM [dbo].[Sample_Goods] AS [Extent1]

FindPagerOrders(int pageSize, int pageIndex, out int totalCount)

-- EF+ Query Future: 1 of 2
SELECT 
    [GroupBy1].[A1] AS [C1]
    FROM ( SELECT 
        COUNT(1) AS [A1]
        FROM [dbo].[Sample_Order] AS [Extent1]
    )  AS [GroupBy1]


-- EF+ Query Future: 2 of 2
SELECT 
    [Extent1].[OrderGuid] AS [OrderGuid], 
    [Extent1].[OrderNo] AS [OrderNo], 
    [Extent1].[OrderCreator] AS [OrderCreator], 
    [Extent1].[OrderDateTime] AS [OrderDateTime], 
    [Extent1].[OrderStatus] AS [OrderStatus], 
    [Extent1].[Description] AS [Description], 
    [Extent1].[Creator] AS [Creator], 
    [Extent1].[CreateDateTime] AS [CreateDateTime], 
    [Extent1].[LastModifier] AS [LastModifier], 
    [Extent1].[LastModifiedDateTime] AS [LastModifiedDateTime]
    FROM [dbo].[Sample_Order] AS [Extent1]
    ORDER BY [Extent1].[CreateDateTime] ASC
    OFFSET 0 ROWS FETCH NEXT 10 ROWS ONLY

FindGoodsMaxWithMinUnitPrice()

-- EF+ Query Future: 1 of 2
SELECT 
    [GroupBy1].[A1] AS [C1]
    FROM ( SELECT 
        MAX([Extent1].[UnitPrice]) AS [A1]
        FROM [dbo].[Sample_Goods] AS [Extent1]
    )  AS [GroupBy1]


-- EF+ Query Future: 2 of 2
SELECT 
    [GroupBy1].[A1] AS [C1]
    FROM ( SELECT 
        MIN([Extent1].[UnitPrice]) AS [A1]
        FROM [dbo].[Sample_Goods] AS [Extent1]
    )  AS [GroupBy1]

至此比较常用到场景，就已经实作完成，大家看到截图和SQL说明都是一次执行，其他大家可以根据 EntityFramework Plus 源代码和文档（不过是英文，但是基本能够看懂），进行更加深入的了解，了解实现原理，我这里还是抛砖引玉一下。

这篇博文的源代码：https://github.com/haibozhou1011/EntityFramework-PlusSample