.NET基础篇——Entity Framework数据转换层通用类
在实现基础的三层开发的时候,大家时常会在数据层对每个实体进行crud的操作,其中存在相当多的重复代码。为了减少重复代码的出现,通常都会定义一个共用类,实现相似的操作,下面为大家介绍一下entity framework时常用到的通用类。
首先在建立起几个关联表:person、company、position,三个实体之间通过导航属性进行相互引用。
下面为大家分别介绍以泛型实现的 create、read、update、delete 操作:
1. create
在objectcontext类之中,早已经为大家预定了一个create 的操作 addobject:
void objectcontext.addobject(entitysetname string,object entity)
void objectset<t>.addobject(t entity)
1 public int add<t>(t entity) where t : entityobject
2 {
3 int changedcount = 0;
4 using (transactionscope scope = new transactionscope(transactionscopeoption.required))
5 {
6 try
7 {
8 using (basicarchitectureentities context = new basicarchitectureentities())
9 {
10 context.addobject(typeof(t).name, entity);
11 changedcount = context.savechanges();
12 if (changedcount > 0)
13 context.acceptallchanges();
14 scope.complete();
15 }
16 }
17 catch (exception ex)
18 { ........ }
19 }
20 return changedcount;
21 }
从下面的测试可以看到,objectcontext.addobject(entitysetname string,object entity)已相当成熟,它不但可以加入单个实体,也可通过导航属性,一次性加入多个关联实体。
1 static void main(string[] args)
2 {
3 basecommand command = new basecommand();
4 //建立关联实体
5 company company = new company() { companyname = "sun" ,address="beijing",telephone="010-87654321"};
6 position position = new position() { positionname = "project manager", salary = 15000.00, company = company };
7 //通过add<t>同时加入实体对象company与position
8 int n=command.add<position>(position);
9
10 console.readkey();
11 }
若要使用批量插入,只要在addobject方法前多加一个重复语言即可,在此就不再多作解释了。
1 public int addlist<t>(list<t> entitylist) where t : entityobject
2 {
3 int changedcount = 0;
4 using (transactionscope scope = new transactionscope(transactionscopeoption.required))
5 {
6 try
7 {
8 using (basicarchitectureentities context = new basicarchitectureentities())
9 {
10 foreach (t entity in entitylist)
11 context.addobject(typeof(t).name, entity);
12 changedcount = context.savechanges();
13 if (changedcount > 0)
14 context.acceptallchanges();
15 scope.complete();
16 }
17 }
18 catch (exception ex)
19 { ....... }
20 }
21 return changedcount;
22 }
2. delete
同样地,objectcontext 类当中也存在方法 objectcontext.deleteobject(object entity)用于删除实体。
首先通过输入的参数 id 建立起entitykey对象,然后在objectcontext查找此实体,若实体存在则使用objectcontext.deleteobject(object entity)方法把此实体删除 。
1 public int delete<t>(int id) where t : entityobject
2 {
3 int changedcount = 0;
4 using (transactionscope scope = new transactionscope(transactionscopeoption.required))
5 {
6 try
7 {
8 using (basicarchitectureentities context = new basicarchitectureentities())
9 {
10 //建立entitykey对象
11 entitykey entitykey = new entitykey("basicarchitectureentities." + typeof(t).name, "id", id);
12 //通过entitykey找到实体
13 var objresult = context.getobjectbykey(entitykey);
14 //若实体存在则删除实体
15 if (objresult != null)
16 context.deleteobject(objresult);
17 changedcount = context.savechanges();
18 if (changedcount > 0)
19 context.acceptallchanges();
20
21 scope.complete();
22 }
23 }
24 catch (exception ex)
25 { ...... }
26 }
27 return changedcount;
28 }
objectcontext.deleteobject(object entity)与objectcontext.addobject(entitysetname string,object entity)相同,可以通过导航属性,一次性删除多个关联实体。但如果数据库中存在下面的数据
company表:
position表:
此时使用此 int delete<company>(2) 方法删除company对象,将会报错。这是由于导航属性在默认情况下具有延时加载的特性,在系统使用objectcontext.getobjectbykey(entitykey)方法加载实体时,它的导航属性不会马上加载到上下文当中。而是在调用该导航属性时,对象才会被加载。
因而系统通过objectcontext.getobjectbykey(2)获取company对象时,对应的position对象并未被加载到上下文当中,所以当删除company对象时,position对象不能被同步删除,因而造成逻辑上的错误。为解决这一问题,可以利用relatedend.load()方法提前加载导航属性。
relatedend是entitycollection<tentity> 、entityreference的父类,它们是特定实体类型的对象集合,该实体类型表示一对多、多对一、多对多的关系。而relatedend.load()方法,可以将一个或多个相关对象提前加载到相关实体当中。
首先通过objectcontext.getobjectbykey(entitykey)方法找到company对象,然后利用反射属性propertyinfo类获取导航属性position,最后使用relatedend.load()方法,把导航属性加载到当前上下文中。此时使用delete<company,position>(2)方法删除company对象时,系统将能正常运行,并把对应的position对象一并删除。
1 public int delete<pkentity, fkentity>(int id)
2 where pkentity : entityobject
3 where fkentity : entityobject
4 {
5 int changedcount = 0;
6 using (transactionscope scope = new transactionscope(transactionscopeoption.required))
7 {
8 try
9 {
10 using (basicarchitectureentities context = new basicarchitectureentities())
11 {
12 //根据软件id建立entitykey对象
13 entitykey entitykey = new entitykey("basicarchitectureentities." + typeof(pkentity).name, "id", id);
14 //根据entitykey查找对应对象
15 pkentity objresult = context.getobjectbykey(entitykey) as pkentity;
16 //根据fkentity加载导航属性
17 propertyinfo propertyinfo = typeof(pkentity).getproperty(typeof(fkentity).name);
18 entitycollection<fkentity> fkentitylist = propertyinfo.getvalue(objresult, null)
19 as entitycollection<fkentity>;
20
21 if (fkentitylist != null)
22 fkentitylist.load();
23
24 if (objresult != null)
25 context.deleteobject(objresult);
26 changedcount = context.savechanges();
27
28 if (changedcount > 0)
29 context.acceptallchanges();
30
31 scope.complete();
32 }
33 }
34 catch (exception ex)
35 { ........ }
36 }
37 return changedcount;
38 }
通过下面的方法也可根据输入的委托predicate,批量删除有关的数据。
1 public int delete<t>(func<t,bool> predicate) where t: entityobject
2 {
3 int changedcount = 0;
4 using (transactionscope scope = new transactionscope(transactionscopeoption.required))
5 {
6 try
7 {
8 using (basicarchitectureentities context = new basicarchitectureentities())
9 {
10 //根据输入的委托查找数据
11 var list = context.createobjectset<t>().where(predicate);
12 //若存在数据,删除有关数据
13 if (list.count() > 0)
14 foreach (var obj in list)
15 context.deleteobject(obj);
16
17 changedcount = context.savechanges();
18 if (changedcount > 0)
19 context.acceptallchanges();
20
21 scope.complete();
22 }
23 }
24 catch (exception ex)
25 { ...... }
26 }
27 return changedcount;
28 }
与前面的例子相同,当使用 delete<company>(x=>x.id==2) 方法删除 company 对象时,由于导航属性 position 处于延迟加载的状态,以致系统无法实现同步删除,从而令数据出现逻辑性的错误。
此时使用类似的方法,利用 relatedend.load() 把导航属性提前加入到上下文中,再删除company对象时,系统就可以把对应 position 对象一并删除。
1 public int delete<pkentity, fkentity>(func<pkentity,bool> predicate)
2 where pkentity : entityobject
3 where fkentity : entityobject
4 {
5 int changedcount = 0;
6 using (transactionscope scope = new transactionscope(transactionscopeoption.required))
7 {
8 try
9 {
10 using (basicarchitectureentities context = new basicarchitectureentities())
11 {
12 //根据输入的委托查找数据
13 var list = context.createobjectset<pkentity>().where(predicate);
14 //若数目大于0,删除有关数据
15 if (list.count() > 0)
16 {
17 foreach (var obj in list)
18 {
19 //在删除前加载其导航属性
20 propertyinfo propertyinfo = typeof(pkentity).getproperty(typeof(fkentity).name);
21 entitycollection<fkentity> fkentitylist = propertyinfo.getvalue(obj, null)
22 as entitycollection<fkentity>;
23 if (fkentitylist.count > 0)
24 fkentitylist.load();
25
26 context.deleteobject(obj);
27 }
28 }
29
30 changedcount = context.savechanges();
31
32 if (changedcount > 0)
33 context.acceptallchanges();
34
35 scope.complete();
36 }
37 }
38 catch (exception ex)
39 { ....... }
40 }
41 return changedcount;
42 }
此时使用delete<company,position>(x=>x.id==2),这样就可以把company对象和相关的position对象同时删除。
3. update
objectcontext 中存在方法 objectcontext.applycurrentvalues<tentity> 和 objectcontext.applyoriginalvalues<tentity>,用于把将标量值从实体复制到 objectcontext 中具有相同主键的对象集中。
注意:在调用此方法前必须把实体预先加载到当前上下文当中,要不然系统将会显示 “objectstatemanager 无法跟踪具有相同键的多个对象” 的错误。
由于dal层的对象大部分使用单体模式进行开发,而basecommand是一个共用对象,在共同操作时,create、delete、read 等操作一般不会对实体造成逻辑性的影响。但如果有多个实体同时调用 update 操作,就有可能对实体造成逻辑性影响。为了避免这一事件的发生,此处使用方法锁定的模式,以 lock(object) 锁定某一对象,以确保在同一时间内只会对一个实体进行更新。
首先通过反射方式获取对象的id,然后通过 objectcontext.getobjectbykey(entitykey) 方法把实体加载到当前上下文当中,最后利用 objectcontext.applycurrentvalues<tentity> 方法,把新加入的实体的属性复制当前上下文。
1 public class basecommand
2 {
3 private object o = new object();
4
5 public int update<t>(t entity) where t : entityobject
6 {
7 lock (o)
8 {
9 int changedcount = 0;
10 type type = typeof(t);
11
12 using (transactionscope scope = new transactionscope(transactionscopeoption.required))
13 {
14 try
15 {
16 using (basicarchitectureentities context = new basicarchitectureentities())
17 {
18 //获取实体的id属性
19 propertyinfo property = type.getproperty("id");
20 object id = property.getvalue(entity, null);
21 //根据id获取上下文中的对应实体
22 entitykey entitykey = new entitykey("basicarchitectureentities."
23 + type.name, "id", id);
24 var objresult = context.getobjectbykey(entitykey);
25 //更新实体属性
26 if (objresult != null)
27 context.applycurrentvalues<t>(type.name, entity);
28
29 changedcount = context.savechanges();
30 if (changedcount > 0)
31 context.acceptallchanges();
32
33 scope.complete();
34 }
35 }
36 catch (exception ex)
37 { ... }
38 }
39 return changedcount;
40 }
41 }
42 }
在一对多,多对一关系时,也可以使用以下方法进行导航属性的同步更新。首先通过反射获取主实体的主键id,然后建立entitykey对象,再通过objectcontext.getobjectbykey(entitykey)方法在当前上下文当中获取此实体,最后通过 objectcontext.applycurrentvalues<tentity> 方法,把新加入的实体的属性复制当前上下文。
下一步就是对导航属性进行更新,首先通过反射获取外键属性,然后对一对多,多对一的关系进行分别处理。在一对多关系时,把导航属性转换成entitycollection<t2>对象集合,然后通过 objectcontext.applycurrentvalues<tentity> 方法对集合中的每个对象进行逐个更新。
在多对一关系时,直接把导航属性转换成t2类型的对象进行更新。
1 public int update<t1, t2>(t1 entity)
2 where t1 : entityobject
3 where t2 : entityobject
4 {
5 lock (o)
6 {
7 int changedcount = 0;
8 type typet1 = typeof(t1);
9 type typet2 = typeof(t2);
10
11 using (transactionscope scope = new transactionscope(transactionscopeoption.required))
12 {
13 try
14 {
15 using (basicarchitectureentities context = new basicarchitectureentities())
16 {
17 propertyinfo property = typet1.getproperty("id");
18 object id = property.getvalue(entity, null);
19
20 //根据软件id建立entitykey对象
21 entitykey entitykey = new entitykey("basicarchitectureentities."
22 + typet1.name, "id", id);
23 //根据entitykey查找对应对象
24 t1 objt1 = context.getobjectbykey(entitykey) as t1;
25 //在上下文中更新当前对象
26 if (objt1 != null)
27 context.applycurrentvalues<t1>(typet1.name, entity);
28
29 //获取外键属性
30 propertyinfo propertyinfo = typet1.getproperty(typet2.name);
31
32 //在一对多关键时更新导航属性
33 var t2list = propertyinfo.getvalue(entity, null)
34 as entitycollection<t2>;
35 if (t2list != null)
36 {
37 foreach (var obj in t2list.tolist())
38 {
39 var oldentity = context.getobjectbykey(obj.entitykey);
40 if (oldentity != null)
41 context.applycurrentvalues<t2>(typet2.name, obj);
42 }
43 }
44
45 //在多对一,一对一关系时更新导航属性
46 var objt2 = propertyinfo.getvalue(entity, null) as t2;
47 if (objt2!= null)
48 {
49 var oldentity = context.getobjectbykey(objt2.entitykey);
50 if (oldentity != null)
51 context.applycurrentvalues<t2>(typet2.name, objt2);
52 }
53
54 changedcount = context.savechanges();
55 if (changedcount > 0)
56 context.acceptallchanges();
57
58 scope.complete();
59 }
60 }
61 catch (exception ex)
62 { ...... }
63 }
64 return changedcount;
65 }
66 }
通过此方法,无论你要通过company同步更新position,还是反过来通过position同步更新company,系统也能正常运行。
4. read
read 是crud中最常见的,下面就为大家介绍最通用的几种方法
4.1 通过id获取单个实体
1 public t getobject<t>(int id) where t : entityobject
2 {
3 try
4 {
5 using (basicarchitectureentities context = new basicarchitectureentities())
6 {
7 entitykey entitykey = new entitykey("basicarchitectureentities."
8 + typeof(t).name, "id", id);
9 var objresult = context.getobjectbykey(entitykey);
10 return objresult as t;
11 }
12 }
13 catch (exception ex)
14 {
15 return null;
16 }
17 }
4.2 通过输入的func<t,bool>委托获取对象
1 public t getobject<t>(func<t,bool> predicate) where t : entityobject
2 {
3 try
4 {
5 using (basicarchitectureentities context = new basicarchitectureentities())
6 {
7 var objectset = context.createobjectset<t>().where(predicate);
8 if (objectset.count() > 0)
9 return objectset.first();
10 else
11 return null;
12 }
13 }
14 catch (exception ex)
15 {
16 return null;
17 }
18 }
4.3通过输入的func<t,bool>委托获取对象,并同时加载单个导航属性
1 public t getobject<t>(func<t, bool> predicate,string includepath)
2 where t : entityobject
3 {
4 try
5 {
6 using (basicarchitectureentities context = new basicarchitectureentities())
7 {
8 var objectquery = context.createobjectset<t>()
9 .include(includepath)
10 .where(predicate);
11
12 if (objectquery.count() > 0)
13 return objectquery.first();
14 else
15 return null;
16 }
17 }
18 catch (exception ex)
19 {
20 return null;
21 }
22 }
4.4通过输入的func<t,bool>委托获取对象,并同时加载多个导航属性
1 public t getobject<t>(func<t, bool> predicate, string[] includepath)
2 where t : entityobject
3 {
4 try
5 {
6 using (basicarchitectureentities context = new basicarchitectureentities())
7 {
8 var list = context.createobjectset<t>().where("1==1");
9
10 foreach (var path in includepath)
11 list=list.include(path);
12
13 var returnvalue = list.where(predicate).tolist();
14
15 if (returnvalue.count() > 0)
16 return returnvalue.first();
17 else
18 return null;
19 }
20 }
21 catch (exception ex)
22 {
23 return null;
24 }
25 }
4.5 通过输入的func<t,bool>委托获取对象集合
1 public ilist<t> getlist<t>(func<t,bool> func) where t:entityobject
2 {
3 try
4 {
5 using (basicarchitectureentities context = new basicarchitectureentities())
6 {
7 objectset<t> objectset = context.createobjectset<t>();
8 ilist<t> list = objectset.where(func).tolist();
9 return list;
10 }
11 }
12 catch (exception ex)
13 {
14 return null;
15 }
16 }
4.6通过输入的func<t,bool>委托获取对象集合,并同时加入单个导航属性
1 public ilist<t> getlist<t>(func<t, bool> func,string includepath)
2 where t : entityobject
3 {
4 try
5 {
6 using (basicarchitectureentities context = new basicarchitectureentities())
7 {
8 objectset<t> objectset = context.createobjectset<t>();
9 ilist<t> list = objectset.include(includepath).where(func).tolist();
10 return list;
11 }
12 }
13 catch (exception ex)
14 {
15 return null;
16 }
17 }
4.7通过输入的func<t,bool>委托获取对象集合,并同时加入多个导航属性
1 public ilist<t> getlist<t>(func<t, bool> func, string[] includepath)
2 where t : entityobject
3 {
4 try
5 {
6 using (basicarchitectureentities context = new basicarchitectureentities())
7 {
8 var list = context.createobjectset<t>().where("1==1");