== 解決 EF where<T>(func) 查詢的一個性能問題
https://www.cnblogs.com/xiaokangufo/p/3901402.html
前兩年幫朋友 做了個網咖管理軟體，採用動軟的三層架構 sql語句生成的。最近因功能變更 要改動，而我這段正在做asp.net mvc +ef+autofac的一個電商網站。索性 就把原來的底層全重新了套用了我現在的架構 EF6.0+autofac+三層架構，上層的asp.net沒有變。改完後發現交班頁面開啟巨慢。
跟蹤EF生成的sql語句 發現生成的sql 有問題，查詢的全表，而全表有近10萬條的資料。
繼續跟蹤資料庫的耗時查詢 發現確實是這條語句佔時間
為什麼會這樣呢，我在查詢裡做條件搜尋了，為啥 結果不對呢？
貼出BaseRepository.cs 的程式碼
public class BaseRepository<T> :IDBbase<T> where T : class { //例項化EF框架 protected skdbContext db = new skdbContext(); //新增 public T AddEntities(T entity) { db.Entry<T>(entity).State = EntityState.Added; db.SaveChanges();View Codereturn 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; } //查詢 public IQueryable<T> LoadEntities(Func<T, bool> wherelambda) { return db.Set<T>().Where<T>(wherelambda).AsQueryable(); } //查詢單個 public T LoadEntitie(Func<T, bool> wherelambda) { return db.Set<T>().FirstOrDefault<T>(wherelambda); } //分頁 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(); //排序獲取當前頁的資料 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(); } }
呼叫程式碼
return jiaobanitem.LoadEntities(t => t.JiaoBanID == jiaobanID && t.GoodsID == GoodsID).FirstOrDefault();
參考nopCommerce 修改baserepository
public class EFRepository<T> : IRepository<T> where T : class { //例項化EF框架 //protected YaFeiNetContext db = new YaFeiNetContext(); private DbContext _context; private IDbSet<T> _entities; public EFRepository(DbContext context) { this._context = context; } //新增 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; } } //查詢 public virtual IQueryable<T> LoadEntities(Func<T, bool> wherelambda) { return this.Entities.Where<T>(wherelambda).AsQueryable(); } //查詢單個 public virtual T LoadEntitie(Func<T, bool> wherelambda) { return this.Table.Where(wherelambda).FirstOrDefault(); } /// <summary> /// 根據主鍵查詢 /// </summary> /// <param name="id"></param> /// <returns></returns> public virtual T GetById(object id) { return this.Entities.Find(id); } //分頁 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(); //排序獲取當前頁的資料 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; } } }View Code
同時修改呼叫程式碼 為
return jiaobanitem.Table.Where(t=>t.JiaoBanID ==jiaobanID && t.GoodsID ==GoodsID).FirstOrDefault();
問題解決 頁面響應不到100ms 同時除錯中 生成的sql語句已經有 查詢條件了
問題出在
//查詢
public IQueryable<T> LoadEntities(Func<T, bool> wherelambda)
{
return db.Set<T>().Where<T>(wherelambda).AsQueryable();
}
為了驗證，我在前臺直接呼叫
return this.context.Set<tb_e_jiaoBanItem>().Where(t => t.JiaoBanID == jiaobanID && t.GoodsID == GoodsID).AsQueryable().FirstOrDefault();
頁面響應也是 100ms左右，效能沒問題。直接呼叫 dbcontext的set<>方法 沒問題。但跨了幾層傳遞後 就有問題。並沒有生成我想要的查詢語句。
這個問題原來別人也碰到過 http://www.cnblogs.com/yjmyzz/archive/2008/09/06/1285564.html
如果傳入Where的引數為Expression，則L2S會自動幫忙處理Expression的拼接；而如果傳入的是Func，而L2S無法拼接Expression與Func，所以只好先把資料全部取出來，然後再應用Func來進行資料過濾。
程式碼應該修改為：
public virtual IEnumerable<T> LoadEntities(System.Linq.Expressions.Expression<Func<T,bool>>wherelambda)
{
return this.Table.Where<T>(wherelambda);
}