== 解决 EF where<T>(func) 查询的一个性能问题

https://www.cnblogs.com/xiaokangufo/p/3901402.html

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() > 0;
        }

        //修改
        public bool DeleteEntities(T entity)
        {
            db.Set<T>().Attach(entity);
            db.Entry<T>(entity).State = EntityState.Deleted;
            return db.SaveChanges() > 0;
        }

        //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 - 1)).
                      Take<T>(pageSize).AsQueryable();
            }
            else
            {
                tempData = tempData.OrderByDescending<T, S>(orderByLambda).
                     Skip<T>(pageSize * (pageIndex - 1)).
                     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() > 0;
            }
            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() > 0;
            }
            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 - 1)).
                          Take<T>(pageSize).AsQueryable();
                }
                else
                {
                    tempData = tempData.OrderByDescending<T, S>(orderByLambda).
                         Skip<T>(pageSize * (pageIndex - 1)).
                         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);
}