EF架构~对不起Include，是我冤枉你了！-白红宇

之前一起认为ＥＦ的延时加载存在性能问题，主要体现在一对多关系上，它会增加与数据库的通讯，而EF本身也提供了“立即加载”include，今天主要说一下它，经过实验，证明如下：

最初接触EF延时加载时，以为只存在这种性能低下的方案，在了解include方法后，才知道这种神奇的方案，它与linq to sql中的DataLoadOptions比较类似，译为立即加载关联对象。

在这里，我对include说一声，对不起，是我冤枉你了，呵呵。

实验代码如下：

Infrastructure层：

　　 public IQueryable
     
       GetWebManageUsers(ISpecification
      
        specification)        {            return base.GetEntities(specification);        }

Domain层：

　　　public List
     
       GetWebManageUsers(DateTime? from, DateTime? to, int? status)        {            //Create specification            UserListSpecification dateSpecification = new UserListSpecification(from, to, status);            var linq = _webManageUsers.GetWebManageUsers(dateSpecification)                                     .Include(i => i.WebManageRoles)                                     .Select(i => new WebManageUsers_Ext                                     {                                         CreateDate = i.CreateDate,                                         ManageUserID = i.ManageUserID,                                         RealName = i.RealName,                                         WebManageRoles = i.WebManageRoles,                                     });             return linq.ToList
      
       ();        }

而前台显示就很简单了，代码省略。

产生的ＳＱＬ代码：

exec sp_executesql N'SELECT [Project1].[ManageUserID] AS [ManageUserID], [Project1].[CreateDate] AS [CreateDate], [Project1].[RealName] AS [RealName], [Project1].[C1] AS [C1], [Project1].[ManageRoleID] AS [ManageRoleID], [Project1].[RoleName] AS [RoleName], [Project1].[DepartmentID] AS [DepartmentID], [Project1].[About] AS [About], [Project1].[UpdateDate] AS [UpdateDate], [Project1].[SortNumber] AS [SortNumber], [Project1].[Operator] AS [Operator], [Project1].[Status] AS [Status], [Project1].[OperatorAuthority] AS [OperatorAuthority]FROM ( SELECT     [Extent1].[ManageUserID] AS [ManageUserID],     [Extent1].[RealName] AS [RealName],     [Extent1].[CreateDate] AS [CreateDate],     [Join1].[ManageRoleID1] AS [ManageRoleID],     [Join1].[RoleName] AS [RoleName],     [Join1].[DepartmentID] AS [DepartmentID],     [Join1].[About] AS [About],     [Join1].[UpdateDate] AS [UpdateDate],     [Join1].[SortNumber] AS [SortNumber],     [Join1].[Operator] AS [Operator],     [Join1].[Status] AS [Status],     [Join1].[OperatorAuthority] AS [OperatorAuthority],     CASE WHEN ([Join1].[ManageUserID] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C1]    FROM  [dbo].[WebManageUsers] AS [Extent1]    LEFT OUTER JOIN  (SELECT [Extent2].[ManageUserID] AS [ManageUserID], [Extent3].[ManageRoleID] AS [ManageRoleID1], [Extent3].[RoleName] AS [RoleName], [Extent3].[DepartmentID] AS [DepartmentID], [Extent3].[About] AS [About], [Extent3].[UpdateDate] AS [UpdateDate], [Extent3].[SortNumber] AS [SortNumber], [Extent3].[Operator] AS [Operator], [Extent3].[Status] AS [Status], [Extent3].[OperatorAuthority] AS [OperatorAuthority]        FROM  [dbo].[WebManageUser_WebManageRoles] AS [Extent2]        INNER JOIN [dbo].[WebManageRoles] AS [Extent3] ON [Extent3].[ManageRoleID] = [Extent2].[ManageRoleID] ) AS [Join1] ON [Extent1].[ManageUserID] = [Join1].[ManageUserID]    WHERE (@p__linq__0 = 1) AND ([Extent1].[CreateDate] > (CASE WHEN (@p__linq__1 IS NULL) THEN @p__linq__2 ELSE @p__linq__1 END)) AND ([Extent1].[CreateDate] < (CASE WHEN (@p__linq__3 IS NULL) THEN @p__linq__4 ELSE @p__linq__3 END)))  AS [Project1]ORDER BY [Project1].[ManageUserID] ASC, [Project1].[C1] ASC',N'@p__linq__0 bit,@p__linq__1 datetime2(7),@p__linq__2 datetime2(7),@p__linq__3 datetime2(7),@p__linq__4 datetime2(7)',@p__linq__0=1,@p__linq__1=NULL,@p__linq__2='0001-01-01 00:00:00',@p__linq__3=NULL,@p__linq__4='9999-12-31 23:59:59.9999999'

从上面代码上分析，主表的字段已经被过滤，include里的表字段无法过滤，这是正常的，呵呵！

最后贡献一下ObjectContext和DbContext环境下，对Include方法的扩展，使它支持lambda表达式。

namespace Domain.Core.Extensions{    ///     /// Class for IQuerable extensions methods    /// 
      
           /// Include method in IQueryable ( base contract for IObjectSet ) is     /// intended for mock Include method in ObjectQuery{T}.    /// Paginate solve not parametrized queries issues with skip and take L2E methods    /// 
          /// 
    public static class IQueryableExtensions    {        #region Extension Methods        ///         /// Include method for IQueryable        /// 
        /// 
     
      Type of elements
             /// Queryable object        /// Path to include        /// 
     
      Queryable object with include path information
             public static IQueryable
     
       Include
      
       (this IQueryable
       
         queryable, string path)            where TEntity : class        {            if (String.IsNullOrEmpty(path))                throw new ArgumentNullException("path can not empty");            //  var query = queryable as ObjectQuery
        
         ;//ObjectContext時用            var query = queryable as DbQuery
         
          ;//DbContext時用            if (query != null)//if is a EF ObjectQuery object                return query.Include(path);            return null;        }        /// 
           /// Include extension method for IQueryable /// 
        /// 
          
           Type of elements in IQueryable
                  /// 
          Queryable object        /// 
          Expression with path to include        /// 
          
           Queryable object with include path information
                  public static IQueryable
          
            Include
           
            (this IQueryable
            
              queryable, Expression
             
              
               > path) where TEntity : class { return Include
               
                (queryable, AnalyzeExpressionPath(path)); } /// 
                 /// Paginate query in a specific page range /// 
 /// 
                
                 Typeof entity in underlying query
                 /// 
                
                 Typeof ordered data value
                 /// 
                Query to paginate /// 
                Order by expression used in paginate method /// 
                
                  /// At this moment Order by expression only support simple order by c=>c.CustomerCode. If you need /// add more complex order functionality don't use this extension method /// 
                 ///  /// 
                Page index /// 
                Page count /// 
                order direction /// 
                
                 A paged queryable
                 [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures")] public static IQueryable
                
                  Paginate
                 
                  (this IQueryable
                  
                    queryable, Expression
                   
                    
                     > orderBy, int pageIndex, int pageCount, bool ascending) where TEntity : class { ObjectQuery
                     
                       query = queryable as ObjectQuery
                      
                       ; if (query != null) { //this paginate method use ESQL for solve problems with Parametrized queries //in L2E and Skip/Take methods string orderPath = AnalyzeExpressionPath
                       
                        (orderBy); return query.Skip(string.Format(CultureInfo.InvariantCulture, "it.{0} {1}", orderPath, (ascending) ? "asc" : "desc"), "@skip", new ObjectParameter("skip", (pageIndex) * pageCount)) .Top("@limit", new ObjectParameter("limit", pageCount)); } else // for In-Memory object set return queryable.OrderBy(orderBy).Skip((pageIndex * pageCount)).Take(pageCount); } #endregion #region Private Methods static string AnalyzeExpressionPath
                        
                         (Expression
                         
                          
                           > expression) where TEntity : class { if (expression == (Expression
                           
                            
                             >)null) throw new ArgumentNullException("Argument error"); MemberExpression body = expression.Body as MemberExpression; if ( ( (body == null) || !body.Member.DeclaringType.IsAssignableFrom(typeof(TEntity)) ) || (body.Expression.NodeType != ExpressionType.Parameter)) { throw new ArgumentException("Argument error"); } else return body.Member.Name; } #endregion }}

非常感谢您的阅读！

有时，一些知识需要我们自己去研究，探索，当你把一些鲜为人知的东西研究出来后，那种喜悦是发自内心的！

本文转自博客园张占岭（仓储大叔）的博客，原文链接：，如需转载请自行联系原博主。