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<WebManageUsers> GetWebManageUsers(ISpecification<WebManageUsers> specification) { return base.GetEntities(specification); }
Domain层：
public List<WebManageUsers> 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<WebManageUsers>(); }
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 { /// <summary> /// Class for IQuerable extensions methods /// <remarks> /// 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 /// </remarks> /// </summary> public static class IQueryableExtensions { #region Extension Methods /// <summary> /// Include method for IQueryable /// </summary> /// <typeparam name="TEntity">Type of elements</typeparam> /// <param name="queryable">Queryable object</param> /// <param name="path">Path to include</param> /// <returns>Queryable object with include path information</returns> public static IQueryable<TEntity> Include<TEntity>(this IQueryable<TEntity> queryable, string path) where TEntity : class { if (String.IsNullOrEmpty(path)) throw new ArgumentNullException("path can not empty"); // var query = queryable as ObjectQuery<TEntity>;//ObjectContext時用 var query = queryable as DbQuery<TEntity>;//DbContext時用 if (query != null)//if is a EF ObjectQuery object return query.Include(path); return null; } /// <summary> /// Include extension method for IQueryable /// </summary> /// <typeparam name="TEntity">Type of elements in IQueryable</typeparam> /// <param name="queryable">Queryable object</param> /// <param name="path">Expression with path to include</param> /// <returns>Queryable object with include path information</returns> public static IQueryable<TEntity> Include<TEntity>(this IQueryable<TEntity> queryable, Expression<Func<TEntity, object>> path) where TEntity : class { return Include<TEntity>(queryable, AnalyzeExpressionPath(path)); } /// <summary> /// Paginate query in a specific page range /// </summary> /// <typeparam name="TEntity">Typeof entity in underlying query</typeparam> /// <typeparam name="S">Typeof ordered data value</typeparam> /// <param name="queryable">Query to paginate</param> /// <param name="orderBy">Order by expression used in paginate method /// <remarks> /// 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 /// </remarks> /// </param> /// <param name="pageIndex">Page index</param> /// <param name="pageCount">Page count</param> /// <param name="ascending">order direction</param> /// <returns>A paged queryable</returns> [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures")] public static IQueryable<TEntity> Paginate<TEntity, S>(this IQueryable<TEntity> queryable, Expression<Func<TEntity, S>> orderBy, int pageIndex, int pageCount, bool ascending) where TEntity : class { ObjectQuery<TEntity> query = queryable as ObjectQuery<TEntity>; if (query != null) { //this paginate method use ESQL for solve problems with Parametrized queries //in L2E and Skip/Take methods string orderPath = AnalyzeExpressionPath<TEntity, S>(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<TEntity, S>(Expression<Func<TEntity, S>> expression) where TEntity : class { if (expression == (Expression<Func<TEntity, S>>)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！
