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Code first 是Microsoft Entity Framework中的一种模式，CodeFirst不会有可视化的界面来进行拖动编辑DataBase-Entity，但会以一个类来进行对数据表关系的描述，以及对所有实体类的描述，优势在于，代码更加地简洁，文件目录更加清晰，也更加便于维护。
直接用实体关系类进行操作，最后SaveChanges，无可厚非，当然可以了，但是，对于一个追求更加简便，更加抽象的程序员来说，无限的封装似乎是一种追求吧，废话不多说，这里直接上EF_Helper_DG的代码->
首先示例性地来一个实体关系类，以便于后面的帮助类的对比，当然，这个类也是不可或缺的。
DBEntity_DG（习惯性地起名）
1 namespace QX_Frame.DAL.Service 2 { 3 using System.Data.Entity; 4 using QX_Frame.Model; 5 6 public partial class DBEntity_DG : DbContext 7 { 8 public DBEntity_DG() 9 : base("name=DBEntity_DG")10 {11 }12 13 public virtual DbSet tb_Class { get; set; }14 public virtual DbSet tb_User { get; set; }15 16 protected override void OnModelCreating(DbModelBuilder modelBuilder)17 {18 modelBuilder.Entity ()19 .Property(e => e.Name)20 .IsFixedLength();21 22 modelBuilder.Entity ()23 .HasMany(e => e.tb_User)24 .WithRequired(e => e.tb_Class)25 .HasForeignKey(e => e.ClassId)26 .WillCascadeOnDelete(false);27 28 modelBuilder.Entity ()29 .Property(e => e.Name)30 .IsFixedLength();31 }32 }33 } 然后，我们来上正菜 EF_DBEntity_DG
1 using LinqKit; //AsExpandable() in linqkit.dll 2 using System; 3 using System.Collections.Generic; 4 using System.IO; 5 using System.Linq; 6 using System.Linq.Expressions; 7 using System.Data.Entity; 8 using QX_Frame.Helper_DG_Framework_4_6; 9 10 namespace QX_Frame.DAL.Service 11 { 12 /* time:2016-10-30 15:26:05 13 author:qixiao 14 */ 15 16 #region The EF_DBEntity_DG visual Interface 17 18 public interface IEF_DBEntity_DG 19 { 20 Boolean IsAdd (T entity); 21 Boolean IsAdd (T entity, out T outEntity); 22 Boolean IsAdd (List entities); 23 24 Boolean IsUpdate (T entity); 25 Boolean IsUpdate (T entity, out T outEntity); 26 27 Boolean IsDelete (T entity); 28 Boolean IsDelete (List entities); 29 Boolean IsDelete (Expression > deleteWhere); 30 31 T selectSingle (Expression > selectWhere); 32 33 List selectAll (); 34 List selectAll (out int Count); 35 List selectAll (Expression > orderBy, Boolean isDESC = false); 36 List selectAll (Expression > orderBy, out int Count, Boolean isDESC = false); 37 List selectAll (Expression > selectWhere); 38 List selectAll (Expression > selectWhere, out int Count); 39 List selectAll (Expression > selectWhere, Expression > orderBy, Boolean isDESC = false); 40 List selectAll (Expression > selectWhere, Expression > orderBy, out int Count, Boolean isDESC = false); 41 42 List selectAllPaging (int pageIndex, int pageSize); 43 List selectAllPaging (int pageIndex, int pageSize, out int Count); 44 List selectAllPaging (int pageIndex, int pageSize, Expression > selectWhere); 45 List selectAllPaging (int pageIndex, int pageSize, Expression > selectWhere, out int Count); 46 List selectAllPaging (int pageIndex, int pageSize, Expression > orderBy, Boolean isDESC = false); 47 List selectAllPaging (int pageIndex, int pageSize, Expression > orderBy, out int Count, Boolean isDESC = false); 48 List selectAllPaging (int pageIndex, int pageSize, Expression > selectWhere, Expression > orderBy, Boolean isDESC = false); 49 List selectAllPaging (int pageIndex, int pageSize, Expression > selectWhere, Expression > orderBy, out int Count, Boolean isDESC = false); 50 } 51 52 #endregion 53 54 public abstract class EF_DBEntity_DG 55 { 56 /*the singleton DBEntity_DG */ 57 /// 58 /// The DBEntity_DG is must be named: DBEntity_DG 59 /// 60 private volatile static DBEntity_DG db = null; 61 62 #region The Singleton to new DBEntity_DG 63 private static readonly object lockHelper = new object(); 64 static EF_DBEntity_DG() 65 { 66 if (db == null) 67 { 68 lock (lockHelper) 69 { 70 if (db == null) 71 db = new DBEntity_DG(); 72 } 73 } 74 //close the Validate of EF OnSaveEnabled 75 db.Configuration.ValidateOnSaveEnabled = false; 76 } 77 #endregion 78 79 /// 80 /// Give the Error Log support 81 /// 82 /// LogText 83 /// The Log Text isAppend or Cover 84 private static void Log_DG(string logText, string logTitle = "DBEntity_DG Error", Boolean isAppend = true) 85 { 86 string LogLocation_DG = @"Log_QX_Frame/Log_QX_Frame_Error/"; 87 try 88 { 89 LogLocation_DG = Config_Helper_DG.AppSetting_Get("Log_Location_Error_DG"); 90 } 91 catch (Exception) 92 { 93 LogLocation_DG = @"Log_QX_Frame/Log_QX_Frame_Error/"; 94 } 95 if (!Directory.Exists(LogLocation_DG)) 96 { 97 Directory.CreateDirectory(LogLocation_DG); 98 } 99 using (StreamWriter log = new StreamWriter(LogLocation_DG + "Log_" + DateTime.Now.Year + DateTime.Now.Month + DateTime.Now.Day + ".Log", isAppend))100 {101 log.WriteLine();102 log.WriteLine(DateTime_Helper_DG.Get_DateTime_Now_24HourType() + " -------" + logTitle + " Log !--------------------");103 log.WriteLine();104 log.WriteLine(logText);105 }106 }107 108 #region Add 109 110 public static Boolean IsAdd (T entity) where T : class111 {112 try113 {114 db.Entry (entity).State = EntityState.Added;115 return db.SaveChanges() > 0;116 }117 catch (Exception ex)118 {119 Log_DG(ex.ToString());120 return false;121 }122 }123 public static Boolean IsAdd (T entity, out T outEntity) where T : class124 {125 try126 {127 db.Entry (entity).State = EntityState.Added;128 outEntity = entity;129 return db.SaveChanges() > 0;130 }131 catch (Exception ex)132 {133 Log_DG(ex.ToString());134 outEntity = default(T);135 return false;136 }137 }138 public static Boolean IsAdd (List entities) where T : class139 {140 try141 {142 db.Set ().AddRange(entities);143 return db.SaveChanges() > 0;144 }145 catch (Exception ex)146 {147 Log_DG(ex.ToString());148 return false;149 }150 }151 152 #endregion153 154 #region Update155 156 public static Boolean IsUpdate (T entity) where T : class157 {158 try159 {160 if (db.Entry (entity).State == EntityState.Detached)161 {162 db.Set ().Attach(entity);163 db.Entry (entity).State = EntityState.Modified;164 }165 return db.SaveChanges() > 0;166 }167 catch (Exception ex)168 {169 Log_DG(ex.ToString());170 return false;171 }172 }173 public static Boolean IsUpdate (T entity, out T outEntity) where T : class174 {175 try176 {177 db.Set ().Attach(entity);178 db.Entry (entity).State = EntityState.Modified;179 outEntity = entity;180 return db.SaveChanges() > 0;181 }182 catch (Exception ex)183 {184 Log_DG(ex.ToString());185 outEntity = default(T);186 return false;187 }188 }189 190 #endregion191 192 #region Delete193 194 public static Boolean IsDelete (T entity) where T : class195 {196 try197 {198 db.Set ().Attach(entity);199 db.Entry (entity).State = EntityState.Deleted;200 return db.SaveChanges() > 0;201 }202 catch (Exception ex)203 {204 Log_DG(ex.ToString());205 return false;206 }207 }208 public static Boolean IsDelete (List entities) where T : class209 {210 try211 {212 db.Set ().RemoveRange(entities);213 return db.SaveChanges() > 0;214 }215 catch (Exception ex)216 {217 Log_DG(ex.ToString());218 return false;219 }220 }221 public static Boolean IsDelete (Expression > deleteWhere) where T : class222 {223 try224 {225 List entitys = db.Set ().AsExpandable().Where(deleteWhere).ToList();226 entitys.ForEach(m => db.Entry (m).State = EntityState.Deleted);227 return db.SaveChanges() > 0;228 }229 catch (Exception ex)230 {231 Log_DG(ex.ToString());232 return false;233 }234 }235 #endregion236 237 #region Select 238 239 public static Boolean IsExist (Expression > selectWhere) where T : class240 {241 try242 {243 return db.Set ().AsExpandable().Where(selectWhere).ToList().FirstOrDefault () == null ? false : true;244 }245 catch (Exception ex)246 {247 Log_DG(ex.ToString());248 return default(Boolean);249 }250 }251 public static T selectSingle (Expression > selectWhere) where T : class252 {253 try254 {255 return db.Set ().AsExpandable().Where(selectWhere).ToList().FirstOrDefault ();256 }257 catch (Exception ex)258 {259 Log_DG(ex.ToString());260 return default(T);261 }262 }263 public static List selectAll () where T : class264 {265 try266 {267 return db.Set ().AsExpandable().ToList();268 }269 catch (Exception ex)270 {271 Log_DG(ex.ToString());272 return default(List );273 }274 }275 public static List selectAll (out int Count) where T : class276 {277 try278 {279 Count = db.Set ().AsExpandable().Count();280 return db.Set ().AsExpandable().ToList();281 }282 catch (Exception ex)283 {284 Log_DG(ex.ToString());285 Count = 0;286 return default(List );287 }288 }289 public static List selectAll (Expression > orderBy, Boolean isDESC = false) where T : class290 {291 try292 {293 if (isDESC)294 return db.Set ().AsExpandable().OrderByDescending(orderBy).ToList();295 else296 return db.Set ().AsExpandable().OrderBy(orderBy).ToList();297 }298 catch (Exception ex)299 {300 Log_DG(ex.ToString());301 return default(List );302 }303 }304 public static List selectAll (Expression > orderBy, out int Count, Boolean isDESC = false) where T : class305 {306 try307 {308 Count = db.Set ().AsExpandable().Count();309 if (isDESC)310 return db.Set ().AsExpandable().OrderByDescending(orderBy).ToList();311 else312 return db.Set ().AsExpandable().OrderBy(orderBy).ToList();313 }314 catch (Exception ex)315 {316 Log_DG(ex.ToString());317 Count = 0;318 return default(List );319 }320 }321 public static List selectAll (Expression > selectWhere) where T : class322 {323 try324 {325 return db.Set ().AsExpandable().Where(selectWhere).ToList();326 }327 catch (Exception ex)328 {329 Log_DG(ex.ToString());330 return default(List );331 }332 }333 public static List selectAll (Expression > selectWhere, out int Count) where T : class334 {335 336 try337 {338 var list = db.Set ().AsExpandable().Where(selectWhere);339 Count = list.Count();340 return list.ToList();341 }342 catch (Exception ex)343 {344 Log_DG(ex.ToString());345 Count = 0;346 return default(List );347 }348 }349 public static List selectAll (Expression > orderBy, Expression > selectWhere, Boolean isDESC = false) where T : class350 {351 try352 {353 if (isDESC)354 return db.Set ().AsExpandable().Where(selectWhere).OrderByDescending(orderBy).ToList();355 else356 return db.Set ().AsExpandable().Where(selectWhere).OrderBy(orderBy).ToList();357 }358 catch (Exception ex)359 {360 Log_DG(ex.ToString());361 return default(List );362 }363 }364 public static List selectAll (Expression > orderBy, Expression > selectWhere, out int Count, Boolean isDESC = false) where T : class365 {366 try367 {368 var list = db.Set ().AsExpandable().Where(selectWhere);369 Count = list.Count();370 if (isDESC)371 return list.OrderByDescending(orderBy).ToList();372 else373 return list.OrderBy(orderBy).ToList();374 }375 catch (Exception ex)376 {377 Log_DG(ex.ToString());378 Count = 0;379 return default(List );380 }381 }382 383 public static List selectAllPaging (int pageIndex, int pageSize, Expression > orderBy, Boolean isDESC = false) where T : class384 {385 try386 {387 var list = db.Set ().AsExpandable();388 if (isDESC)389 return list.OrderByDescending(orderBy).Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList();390 else391 return list.OrderBy(orderBy).Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList();392 }393 catch (Exception ex)394 {395 Log_DG(ex.ToString());396 return default(List );397 }398 }399 public static List selectAllPaging (int pageIndex, int pageSize, Expression > orderBy, out int Count, Boolean isDESC = false) where T : class400 {401 try402 {403 var list = db.Set ().AsExpandable();404 Count = list.Count();405 if (isDESC)406 return list.OrderByDescending(orderBy).Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList();407 else408 return list.OrderBy(orderBy).Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList();409 }410 catch (Exception ex)411 {412 Log_DG(ex.ToString());413 Count = 0;414 return default(List );415 }416 }417 public static List selectAllPaging (int pageIndex, int pageSize, Expression > orderBy, Expression > selectWhere, Boolean isDESC = false) where T : class418 {419 try420 {421 var list = db.Set ().AsExpandable().Where(selectWhere);422 if (isDESC)423 return list.OrderByDescending(orderBy).Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList();424 else425 return list.OrderBy(orderBy).Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList();426 }427 catch (Exception ex)428 {429 Log_DG(ex.ToString());430 return default(List );431 }432 }433 public static List selectAllPaging (int pageIndex, int pageSize, Expression > orderBy, Expression > selectWhere, out int Count, Boolean isDESC = false) where T : class434 {435 try436 {437 var list = db.Set ().AsExpandable().Where(selectWhere);438 Count = list.Count();439 if (isDESC)440 return list.OrderByDescending(orderBy).Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList();441 else442 return list.OrderBy(orderBy).Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList();443 }444 catch (Exception ex)445 {446 Log_DG(ex.ToString());447 Count = 0;448 return default(List );449 }450 }451 452 #endregion453 }454 } 这里说明一下：
1、IEF_DBEntity_DG 帮助类的接口，当然我没有继承这个接口，这个接口只是我以后回顾的时候看的，并没有实际使用价值，只作为说明性的文字，不喜勿碰哈。
2、采用单例模式，这里不做过多说明，单例的介绍铺天盖地，我只是说，使用的时候，需要在这里改动两处对应到实体关系类上。
3、使用泛型，泛型在帮助类的重要性不必多说了吧，写帮助类不用泛型...啧啧啧。
4、Log_DG 这里直接封装了EF操作的错误信息，一般在try catch中调用，对错误进行日志的描述，便于后续的错误查找。
5、里面分别封装了 增加、删除、修改、查询四种基础的操作，并且每种操作都附有大量的重载（尤其是查询）便于适应更多不断变化项目；还有一些是快捷的操作，IsExist 这里直接返回数据是否存在。
6、所有的条件采用lambda表达式的方式，lambda表达式是比较新颖比较方便的条件判断条件筛选方式之一，在未来会更多地使用lambda表达式进行操作，在C#6.0已然是得到了很大的支持。
7、恰到适宜的out 输出参数，保证了在需要插入并且需要插入的结果需求的使用。
8、查询的分页支持，不必再写繁琐的分页，这里已经对分页进行了支持。
具体内容，参考类详情吧，后续更新修改，敬请期待！ --柒小 2016年12月21日22:34:01
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