== 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);
}
