以下小编整理的entity framework常见错误的汇总,大家如果还有不明白可以在下面留言区讨论。
1 实体属性配置为isrequired()对更新的影响
抛出异常类型dbentityvalidationexception
表结构:
实体:
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public class user { public int id { get; set; } /// < summary > /// 账号 /// </ summary > public string account { get; set; } /// < summary > /// 邮箱 /// </ summary > public string email { get; set; } /// < summary > /// 昵称 /// </ summary > public string nickname { get; set; } /// < summary > /// 头像 /// </ summary > public string avatarid { get; set; } /// < summary > /// 记录插入时间 /// </ summary > public datetime inserttime { get; set; } /// < summary > /// 记录修改时间 /// </ summary > public datetime updatetime { get; set; } } |
实体配置:
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modelbuilder.entity< user >().property(u => u.account) .isrequired() .isunicode(false) .hasmaxlength(50); modelbuilder.entity< user >().property(u => u.email) .isrequired() .isunicode(false) .hasmaxlength(100); modelbuilder.entity< user >().property(u => u.nickname) .isunicode(false) .hasmaxlength(50); modelbuilder.entity< user >().property(u => u.avatarid) .isoptional() .hasmaxlength(100); |
customdbcontext继承自dbcontext
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[dbconfigurationtype(typeof(mysqlefconfiguration))] public class customdbcontext : dbcontext { public customdbcontext() : base("name=master") { this.configuration.lazyloadingenabled = false; //dropcreatedatabaseifmodelchanges //new dropcreatedatabasealways< customdbcontext >() database.setinitializer< customdbcontext >(null); } public dbset< user > users { get; set; } protected override void onmodelcreating(dbmodelbuilder modelbuilder) { base.onmodelcreating(modelbuilder); entityconfiguration.set(modelbuilder); } } |
更新操作:
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using (customdbcontext db = new customdbcontext()) { user user = new user { id = 1, email = "test@1622.com", }; dbentityentry< user > entry = db.entry< user >(user); entry.state = entitystate.unchanged; entry.property(t => t.email).ismodified = true; int num = db.savechanges(); } |
执行操作,报错信息如下:
查看entityvalidationerrors,
只能看到{system.data.entity.validation.dbentityvalidationresult},没有更详细的信息。
如果将上述代码用try..catch包起来,如下写法:
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try { //执行代码 } catch (dbentityvalidationexception ex) { var e = ex.entityvalidationerrors; } catch (exception ex) { } |
一层一层地打开,看到真正导致异常的原因,看到下面的截图:
分析实体配置发现,account属性被设置为isrequired,那么在更新实体的时候,即使不更新这个字段,也要给这个字段赋值,那么赋值后观察:
更新操作代码变为
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using (customdbcontext db = new customdbcontext()) { user user = new user { id = 1, email = "test@1622.com", account = "a" }; dbentityentry< user > entry = db.entry< user >(user); entry.state = entitystate.unchanged; entry.property(t => t.email).ismodified = true; int num = db.savechanges(); } |
经过上述调整后,更新成功。
那么换一个思路,将account属性被设置为isoptional()是不是也可以呢?
修改实体配置,将account属性设置按如下修改,并注掉上面的account = "a"
modelbuilder.entity<user>().property(u => u.account)
.isoptional()
.isunicode(false)
.hasmaxlength(50);
执行测试,更改成功。
得出结论:在实体配置时,指定了为必选的字段,那么更新操作时,构造实例一定要对必选(isrequired())字段赋值。
上述测试中还有一个值得考虑的细节,构造user实例的时候,只对id,email进行了赋值,而没有对其他属性进行赋值,那么为什么会成功呢?那么必定是未进行任何设置的实体属性默认是isoptional()。这跟表结构中的字段类型设置为not null有无关联呢,从测试结果看就本类应用无必然联系。
总结:
a.实体配置中指定了实体属性为isrequired(),更新操作构造类的实例时必对此属性赋值。
b.不进行配置的实体属性默认为isoptional()
c.表结构中字段是否为not null对上述规则无影响。
2 更新报错:
an object with the same key already exists in the objectstatemanager. the objectstatemanager cannot track multiple objects with the same key.
异常类型:system.data.entity.infrastructure.dbupdateconcurrencyexception
实体属性配置如上例所示。
操作代码:
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using (customdbcontext db = new customdbcontext()) { user user = new user { id = 1, email = "test@132.com", }; dbentityentry< user > entry = db.entry< user >(user); entry.state = entitystate.unchanged; entry.property(t => t.email).ismodified = true; user user1 = new user { id = 1, email = "test@132.com", }; dbentityentry< user > entry1 = db.entry< user >(user1); entry1.state = entitystate.unchanged; entry1.property(t => t.email).ismodified = true; int num = db.savechanges(); } |
执行操作
涉及到两次修改操作,两次操作构造了两个实例,但是实例的属性id有相同的值。
如果两次操作的是同一个实例,而不是不同的实例,那么不会抛出异常,代码如下:
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using (customdbcontext db = new customdbcontext()) { user user = new user { id = 1, email = "test@132.com", }; dbentityentry< user > entry = db.entry< user >(user); entry.state = entitystate.unchanged; entry.property(t => t.email).ismodified = true; dbentityentry< user > entry1 = db.entry< user >(user); entry1.state = entitystate.unchanged; entry1.property(t => t.email).ismodified = true; int num = db.savechanges(); } |
3 未给主键赋值或赋给主键一个不存在的值,抛出异常
system.data.entity.infrastructure.dbupdateconcurrencyexception
操作代码如下,其中id=1这条语句被注掉,id是主键:
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using (customdbcontext db = new customdbcontext()) { user user = new user { //id = 1, email = "test@132.com", }; dbentityentry< user > entry = db.entry< user >(user); entry.state = entitystate.unchanged; entry.property(t => t.email).ismodified = true; int num = db.savechanges(); } |
运行上述代码,抛出异常信息如下,注意异常类型居然是system.data.entity.infrastructure.dbupdateconcurrencyexception,看上去像是并发问题,但实际却不是!
message:
store update, insert, or delete statement affected an unexpected number of rows (0). entities may have been modified or deleted since entities were loaded. refresh objectstatemanager entries.
赋给主键一个不存在的值,令id=4(在数据库表中不存在id为4的一条记录)抛出的异常与上面的相同。
4 字段超长抛出异常:system.data.entity.validation.dbentityvalidationexception
表中nickname 字段定义为50个字符,现在赋值超过50。
操作代码如下:
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using (customdbcontext db = new customdbcontext()) { user user = new user { id = 4, email = "test@132.com", nickname = "testupdateerrortestupdateerrortestupdateerrortestupdateerrortestupdateerrortestupdateerrortestupdateerrortestupdateerrortestupdateerrortestupdateerrortestupdateerror" }; dbentityentry< user > entry = db.entry< user >(user); entry.state = entitystate.unchanged; entry.property(t => t.email).ismodified = true; int num = db.savechanges(); } |
运行程序报错:
一层一层点开,查看具体原因:
原文链接:https://www.cnblogs.com/hdwgxz/p/7897031.html