解决 EF where<T>(func) 查询的一个性能问题

前两年帮朋友 做了个网吧管理软件，采用动软的三层架构 sql语句生成的。最近因功能变更 要改动，而我这段正在做asp.net mvc +ef+autofac的一个电商网站。索性 就把原来的底层全重新了套用了我现在的架构 EF6.0+autofac+三层架构，上层的asp.net没有变。改完后发现交班页面打开巨慢。

跟踪EF生成的sql语句   发现生成的sql 有问题，查找的全表，而全表有近10万条的数据。

继续跟踪数据库的耗时查询 发现确实是这条语句占时间

为什么会这样呢，我在查询里做条件搜索了，为啥 结果不对呢？

贴出 BaseRepository.cs 的代码

 public class BaseRepository<T> :IDBbase<T>  where T : class
     {
         //实例化EF框架
        protected skdbContext db = new skdbContext();

         //添加
         public T AddEntities(T entity)
         {
             db.Entry<T>(entity).State = EntityState.Added;
             db.SaveChanges();
             return entity;
         }

         //修改
         public bool UpdateEntity(T entity)
         {
             db.Set<T>().Attach(entity);
             db.Entry<T>(entity).State = EntityState.Modified;
             return db.SaveChanges() > ;
         }

         //修改
         public bool DeleteEntities(T entity)
         {
             db.Set<T>().Attach(entity);
             db.Entry<T>(entity).State = EntityState.Deleted;
             return db.SaveChanges() > ;
         }

         //查询
         public IQueryable<T> LoadEntities(Func<T, bool> wherelambda)
         {
             return db.Set<T>().Where<T>(wherelambda).AsQueryable();
         }
         //查询单个
         public T LoadEntitie(Func<T, bool> wherelambda)
         {
             return db.Set<T>().FirstOrDefault<T>(wherelambda);
         }

         //分页
         public IQueryable<T> LoadPagerEntities<S>(int pageSize, int pageIndex, out int total,
             Func<T, bool> whereLambda, bool isAsc, Func<T, S> orderByLambda)
         {
             var tempData = db.Set<T>().Where<T>(whereLambda);

             total = tempData.Count();

             //排序获取当前页的数据
             if (isAsc)
             {
                 tempData = tempData.OrderBy<T, S>(orderByLambda).
                       Skip<T>(pageSize * (pageIndex - )).
                       Take<T>(pageSize).AsQueryable();
             }
             else
             {
                 tempData = tempData.OrderByDescending<T, S>(orderByLambda).
                      Skip<T>(pageSize * (pageIndex - )).
                      Take<T>(pageSize).AsQueryable();
             }
             return tempData.AsQueryable();
         }
     }

调用代码

return jiaobanitem.LoadEntities(t => t.JiaoBanID == jiaobanID && t.GoodsID == GoodsID).FirstOrDefault();

参考 nopCommerce  修改baserepository

 public class EFRepository<T> : IRepository<T> where T : class
     {
         //实例化EF框架
        //protected YaFeiNetContext db = new YaFeiNetContext();
        private DbContext _context;
        private IDbSet<T> _entities;

        public EFRepository(DbContext context)
        {
            this._context = context;
        }

         //添加
         public virtual T AddEntities(T entity)
         {
             try
             {
                 if(entity==null)
                     throw new ArgumentNullException("entity");

                 this.Entities.Add(entity);
                 this._context.SaveChanges();
                 return entity;
             }
             catch(DbEntityValidationException dbEx)
             {
                 var msg = string.Empty;
                 foreach(var validationErrors in dbEx.EntityValidationErrors)
                     foreach (var validationError in validationErrors.ValidationErrors)
                         msg += string.Format("Property:{0} Error:{1}", validationError.PropertyName, validationError.ErrorMessage) + Environment.NewLine ;

                 var fail = new Exception(msg,dbEx);
                 throw fail;
             }
         }

         //修改
         public virtual bool UpdateEntities(T entity)
         {
             try
             {
                 if (entity == null)
                     throw new ArgumentNullException("entity");

                // this.Entities.Attach(entity);
                // _context.Entry<T>(entity).State = EntityState.Modified;
                 return this._context.SaveChanges() > ;
             }
             catch (DbEntityValidationException dbEx)
             {
                 var msg = string.Empty;
                 foreach (var validationErrors in dbEx.EntityValidationErrors)
                     foreach (var validationError in validationErrors.ValidationErrors)
                         msg += string.Format("Property:{0} Error:{1}", validationError.PropertyName, validationError.ErrorMessage) + Environment.NewLine;

                 var fail = new Exception(msg, dbEx);
                 throw fail;
             }

         }

         //修改
         public virtual bool DeleteEntities(T entity)
         {
             try
             {
                 if (entity == null)
                     throw new ArgumentNullException("entity");

                 //db2.Set<T>().Attach(entity);
                 //db2.Entry<T>(entity).State = EntityState.Deleted;
                 this.Entities.Remove(entity);
                 return this._context.SaveChanges() > ;
             }
             catch (DbEntityValidationException dbEx)
             {
                 var msg = string.Empty;
                 foreach (var validationErrors in dbEx.EntityValidationErrors)
                     foreach (var validationError in validationErrors.ValidationErrors)
                         msg += string.Format("Property:{0} Error:{1}", validationError.PropertyName, validationError.ErrorMessage) + Environment.NewLine;

                 var fail = new Exception(msg, dbEx);
                 throw fail;
             }

         }

         //查询
         public virtual IQueryable<T> LoadEntities(Func<T, bool> wherelambda)
         {
             return this.Entities.Where<T>(wherelambda).AsQueryable();
         }
         //查询单个
         public virtual T LoadEntitie(Func<T, bool> wherelambda)
         {
             return this.Table.Where(wherelambda).FirstOrDefault();
         }
        /// <summary>
        /// 根据主键查找
        /// </summary>
        /// <param name="id"></param>
        /// <returns></returns>
         public virtual T GetById(object id)
         {
             return this.Entities.Find(id);
         }

         //分页
         public virtual IQueryable<T> LoadPagerEntities<S>(int pageSize, int pageIndex, out int total,
             Func<T, bool> whereLambda, bool isAsc, Func<T, S> orderByLambda)
         {

             var tempData = this.Entities.Where<T>(whereLambda);

                 total = tempData.Count();

                 //排序获取当前页的数据
                 if (isAsc)
                 {
                     tempData = tempData.OrderBy<T, S>(orderByLambda).
                           Skip<T>(pageSize * (pageIndex - )).
                           Take<T>(pageSize).AsQueryable();
                 }
                 else
                 {
                     tempData = tempData.OrderByDescending<T, S>(orderByLambda).
                          Skip<T>(pageSize * (pageIndex - )).
                          Take<T>(pageSize).AsQueryable();
                 }
                 return tempData.AsQueryable();

         }

         protected virtual IDbSet<T> Entities
         {
             get
             {
                 if (_entities == null)
                     _entities = _context.Set<T>();
                 return _entities;
             }
         }

         public virtual IQueryable<T> Table
         {
             get { return this.Entities; }
         }

     }

同时修改调用代码 为

return jiaobanitem.Table.Where(t=>t.JiaoBanID ==jiaobanID && t.GoodsID ==GoodsID).FirstOrDefault();

问题解决 页面响应不到100ms   同时调试中 生成的sql语句已经有 查询条件了

问题出在

//查询
public IQueryable<T> LoadEntities(Func<T, bool> wherelambda)
{
　　return db.Set<T>().Where<T>(wherelambda).AsQueryable();
}

为了验证，我在前台直接调用

return this.context.Set<tb_e_jiaoBanItem>().Where(t => t.JiaoBanID == jiaobanID && t.GoodsID == GoodsID).AsQueryable().FirstOrDefault();

页面响应也是 100ms左右，性能没问题。直接调用 dbcontext的set<>方法 没问题。但跨了几层传递后 就有问题。并没有生成我想要的查询语句。

这个问题原来别人也碰到过  http://www.cnblogs.com/yjmyzz/archive/2008/09/06/1285564.html

如果传入Where的参数为Expression，则L2S会自动帮忙处理Expression的拼接；而如果传入的是Func，而L2S无法拼接Expression与Func，所以只好先把数据全部取出来，然后再应用Func来进行数据过滤。

代码应该修改为：

public virtual IEnumerable<T> LoadEntities(System.Linq.Expressions.Expression<Func<T,bool>> wherelambda)
{
return this.Table.Where<T>(wherelambda);
}