blocks|key|295322|text|你基本上有两个选择：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|295323|295324|一直执行EF，在这种情况下，您将根据提供的userId加载对象-整个对象已加载|unordered-list-item|offset|length|style|CODE|295325|更新password字段|295326|使用上下文的.SaveChanges()+method|295327|保存对象|295328|​|295329|在这种情况下，这取决于EF如何详细处理这一问题。我刚刚测试了这一点，在我只更改对象的单个字段的情况下，EF创建的内容也与您手动创建的内容基本相同-类似于：|295330|`UPDATE+dbo.Users+SET+Password+=+@Password+WHERE+UserId+=+@UserId`|code-block|syntax|javascript|295331|因此，EF足够聪明，可以找出哪些列确实发生了更改，并且它将创建一个T-SQL语句来处理那些实际上需要的更新。|295332|295333|您可以在T-SQL代码中定义一个执行所需操作的存储过程(只更新给定UserId的Password列，而不执行其他任何操作-基本上执行UPDATE+dbo.Users+SET+Password+=+@Password+WHERE+UserId+=+@UserId)，然后在EF模型中为该存储过程创建一个函数导入，然后调用该函数，而不是执行上面概述的|295334|步骤|295335|entityMap^0|0|0|L|6|0|2|8|0|6|E|0|0|0|0|0|0|0|X|6|14|8|1U|1S|0|0^^$0|@$1|2|3|4|5|6|7|17|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|18|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|19|8|@$F|1A|G|1B|H|I]]|9|@]|A|$]]|$1|J|3|K|5|E|7|1C|8|@$F|1D|G|1E|H|I]]|9|@]|A|$]]|$1|L|3|M|5|E|7|1F|8|@$F|1G|G|1H|H|I]]|9|@]|A|$]]|$1|N|3|O|5|6|7|1I|8|@]|9|@]|A|$]]|$1|P|3|Q|5|6|7|1J|8|@]|9|@]|A|$]]|$1|R|3|S|5|6|7|1K|8|@]|9|@]|A|$]]|$1|T|3|U|5|V|7|1L|8|@]|9|@]|A|$W|X]]|$1|Y|3|Z|5|6|7|1M|8|@]|9|@]|A|$]]|$1|10|3|-4|5|6|7|1N|8|@]|9|@]|A|$]]|$1|11|3|12|5|E|7|1O|8|@$F|1P|G|1Q|H|I]|$F|1R|G|1S|H|I]|$F|1T|G|1U|H|I]]|9|@]|A|$]]|$1|13|3|14|5|6|7|1V|8|@]|9|@]|A|$]]|$1|15|3|-4|5|6|7|1W|8|@]|9|@]|A|$]]]|16|$]]

You have basically two options:

<ul>
<li>go the EF way all the way, in that case, you would

<ul>
<li>load the object based on the <code>userId</code> provided - the entire object gets loaded</li>
<li>update the <code>password</code> field</li>
<li>save the object back using the context's <code>.SaveChanges()</code> method</li>
</ul></li>
</ul>

In this case, it's up to EF how to handle this in detail. I just tested this, and in the case I only change a single field of an object, what EF creates is pretty much what you'd create manually, too - something like:

<pre><code>`UPDATE dbo.Users SET Password = @Password WHERE UserId = @UserId`
</code></pre>

So EF is smart enough to figure out what columns have indeed changed, and it will create a T-SQL statement to handle just those updates that are in fact necessary.

<ul>
<li>you define a stored procedure that does exactly what you need, in T-SQL code (just update the <code>Password</code> column for the given <code>UserId</code> and nothing else - basically executes <code>UPDATE dbo.Users SET Password = @Password WHERE UserId = @UserId</code>) and you create a function import for that stored procedure in your EF model and you call this function instead of doing the steps outlined above</li>
</ul>

blocks|key|295337|text|您可以通过以下方式告诉EF哪些属性需要更新：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|295338|public+void+ChangePassword(int+userId,+string+password)
{
++var+user+=+new+User+{+Id+=+userId,+Password+=+password+};
++using+(var+context+=+new+ObjectContext(ConnectionString))
++{
++++var+users+=+context.CreateObjectSet<User>();
++++users.Attach(user);
++++context.ObjectStateManager.GetObjectStateEntry(user)
++++++.SetModifiedProperty("Password");
++++context.SaveChanges();
++}
}|code-block|syntax|javascript|295339|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can tell EF which properties have to be updated in this way:

<pre><code>public void ChangePassword(int userId, string password)
{
 var user = new User { Id = userId, Password = password };
 using (var context = new ObjectContext(ConnectionString))
 {
 var users = context.CreateObjectSet&lt;User&gt;();
 users.Attach(user);
 context.ObjectStateManager.GetObjectStateEntry(user)
 .SetModifiedProperty("Password");
 context.SaveChanges();
 }
}
</code></pre>

blocks|key|295341|text|Ladislav的答案更新为使用DbContext+(在EF+4.1中引入)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|295342|public+void+ChangePassword(int+userId,+string+password)
{
++++var+user+=+new+User()+{+Id+=+userId,+Password+=+password+};
++++using+(var+db+=+new+MyEfContextName())
++++{
++++++++db.Users.Attach(user);
++++++++db.Entry(user).Property(x+=>+x.Password).IsModified+=+true;
++++++++db.SaveChanges();
++++}
}|code-block|syntax|javascript|295343|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Ladislav's answer updated to use DbContext (introduced in EF 4.1):
<pre class="lang-cs prettyprint-override"><code>public void ChangePassword(int userId, string password)
{
 var user = new User() { Id = userId, Password = password };
 using (var db = new MyEfContextName())
 {
 db.Users.Attach(user);
 db.Entry(user).Property(x =&gt; x.Password).IsModified = true;
 db.SaveChanges();
 }
}
</code></pre>

blocks|key|3238529|text|我使用的是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3238530|实体：|3238531|public+class+Thing+
{
++++[Key]
++++public+int+Id+{+get;+set;+}
++++public+string+Info+{+get;+set;+}
++++public+string+OtherStuff+{+get;+set;+}
}|code-block|syntax|javascript|3238532|dbcontext：|3238533|public+class+MyDataContext+:+DbContext
{
++++public+DbSet<Thing+>+Things+{+get;+set;+}
}|3238534|访问器代码：|3238535|MyDataContext+ctx+=+new+MyDataContext();

//+FIRST+create+a+blank+object
Thing+thing+=+ctx.Things.Create();

//+SECOND+set+the+ID
thing.Id+=+id;

//+THIRD+attach+the+thing+(id+is+not+marked+as+modified)
db.Things.Attach(thing);+

//+FOURTH+set+the+fields+you+want+updated.
thing.OtherStuff+=+"only+want+this+field+updated.";

//+FIFTH+save+that+thing
db.SaveChanges();|3238536|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

i'm using this:

entity:

<pre><code>public class Thing 
{
 [Key]
 public int Id { get; set; }
 public string Info { get; set; }
 public string OtherStuff { get; set; }
}
</code></pre>

dbcontext:

<pre><code>public class MyDataContext : DbContext
{
 public DbSet&lt;Thing &gt; Things { get; set; }
}
</code></pre>

accessor code:

<pre><code>MyDataContext ctx = new MyDataContext();

// FIRST create a blank object
Thing thing = ctx.Things.Create();

// SECOND set the ID
thing.Id = id;

// THIRD attach the thing (id is not marked as modified)
db.Things.Attach(thing); 

// FOURTH set the fields you want updated.
thing.OtherStuff = "only want this field updated.";

// FIFTH save that thing
db.SaveChanges();
</code></pre>

blocks|key|3238572|text|我在这里玩得很晚，但这就是我正在做的事情，我花了一段时间寻找一个我感到满意的解决方案；这只会为更改的字段生成一条UPDATE语句，因为您可以通过“白名单”概念明确定义它们是什么，这对防止web表单注入更安全。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3238573|摘自我的ISession数据存储库：|3238574|public+bool+Update<T>(T+item,+params+string[]+changedPropertyNames)+where+T+
++:+class,+new()
{
++++_context.Set<T>().Attach(item);
++++foreach+(var+propertyName+in+changedPropertyNames)
++++{
++++++++//+If+we+can't+find+the+property,+this+line+wil+throw+an+exception,+
++++++++//which+is+good+as+we+want+to+know+about+it
++++++++_context.Entry(item).Property(propertyName).IsModified+=+true;
++++}
++++return+true;
}|code-block|syntax|javascript|3238575|如果您愿意，可以将其封装在try..catch中，但我个人希望我的调用者了解此场景中的异常。|3238576|它的调用方式类似于这样(对我来说，这是通过一个ASP.NET+Web+API)：|3238577|if+(!session.Update(franchiseViewModel.Franchise,+new[]
++++{
++++++"Name",
++++++"StartDate"
++}))
++throw+new+HttpResponseException(new+HttpResponseMessage(HttpStatusCode.NotFound));|3238578|entityMap^0|1K|6|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|X|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|Y|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|Z|8|@]|D|@]|E|$]]|$1|O|3|P|5|6|7|10|8|@]|D|@]|E|$]]|$1|Q|3|R|5|J|7|11|8|@]|D|@]|E|$K|L]]|$1|S|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|T|$]]

I'm late to the game here, but this is how I am doing it, I spent a while hunting for a solution I was satisified with; this produces an <code>UPDATE</code> statement ONLY for the fields that are changed, as you explicitly define what they are through a "white list" concept which is more secure to prevent web form injection anyway.

An excerpt from my ISession data repository:

<pre><code>public bool Update&lt;T&gt;(T item, params string[] changedPropertyNames) where T 
 : class, new()
{
 _context.Set&lt;T&gt;().Attach(item);
 foreach (var propertyName in changedPropertyNames)
 {
 // If we can't find the property, this line wil throw an exception, 
 //which is good as we want to know about it
 _context.Entry(item).Property(propertyName).IsModified = true;
 }
 return true;
}
</code></pre>

This could be wrapped in a try..catch if you so wished, but I personally like my caller to know about the exceptions in this scenario.

It would be called in something like this fashion (for me, this was via an ASP.NET Web API):

<pre><code>if (!session.Update(franchiseViewModel.Franchise, new[]
 {
 "Name",
 "StartDate"
 }))
 throw new HttpResponseException(new HttpResponseMessage(HttpStatusCode.NotFound));
</code></pre>

blocks|key|3024222|text|在寻找这个问题的解决方案时，我通过Patrick+Desjardins'+blog发现了GONeale答案的一个变体|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3024223|public+int+Update(T+entity,+Expression<Func<T,+object>>[]+properties)
{
++DatabaseContext.Entry(entity).State+=+EntityState.Unchanged;
++foreach+(var+property+in+properties)
++{
++++var+propertyName+=+ExpressionHelper.GetExpressionText(property);
++++DatabaseContext.Entry(entity).Property(propertyName).IsModified+=+true;
++}
++return+DatabaseContext.SaveChangesWithoutValidation();
}|code-block|syntax|javascript|3024224|3024225|“正如你所看到的，它接受一个函数的表达式作为它的第二个参数。这将允许通过在Lambda表达式中指定要更新的属性来使用此方法。”|blockquote|3024226|3024227|3024228|...Update(Model,+d=>d.Name);
//or
...Update(Model,+d=>d.Name,+d=>d.SecondProperty,+d=>d.AndSoOn);|3024229|(这里也给出了一个类似的解决方案：https://stackoverflow.com/a/5749469/2115384+)|3024230|我目前在自己的代码中使用的方法，扩展为也可以处理类型为ExpressionType.Convert的(Linq)表达式。在我的例子中，这是必要的，例如使用Guid和其他对象属性。它们被“包装”在Convert()中，因此不能由System.Web.Mvc.ExpressionHelper.GetExpressionText__处理。|style|CODE|3024231|public+int+Update(T+entity,+Expression<Func<T,+object>>[]+properties)
{
++++DbEntityEntry<T>+entry+=+dataContext.Entry(entity);
++++entry.State+=+EntityState.Unchanged;
++++foreach+(var+property+in+properties)
++++{
++++++++string+propertyName+=+"";
++++++++Expression+bodyExpression+=+property.Body;
++++++++if+(bodyExpression.NodeType+==+ExpressionType.Convert+&&+bodyExpression+is+UnaryExpression)
++++++++{
++++++++++++Expression+operand+=+((UnaryExpression)property.Body).Operand;
++++++++++++propertyName+=+((MemberExpression)operand).Member.Name;
++++++++}
++++++++else
++++++++{
++++++++++++propertyName+=+System.Web.Mvc.ExpressionHelper.GetExpressionText(property);
++++++++}
++++++++entry.Property(propertyName).IsModified+=+true;
++++}

++++dataContext.Configuration.ValidateOnSaveEnabled+=+false;
++++return+dataContext.SaveChanges();
}|3024232|entityMap|0|LINK|mutability|MUTABLE|url|http://patrickdesjardins.com/blog/how-to-update-specific-field-of-your-entity-with-a-generic-method-and-entity-framework|1|https://stackoverflow.com/a/5749469/2115384^0|H|O|0|0|0|0|0|0|0|0|H|17|1|0|R|M|25|4|35|1D|0|0^^$0|@$1|2|3|4|5|6|7|18|8|@]|9|@$A|19|B|1A|1|1B]]|C|$]]|$1|D|3|E|5|F|7|1C|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|1D|8|@]|9|@]|C|$]]|$1|J|3|K|5|L|7|1E|8|@]|9|@]|C|$]]|$1|M|3|-4|5|6|7|1F|8|@]|9|@]|C|$]]|$1|N|3|-4|5|6|7|1G|8|@]|9|@]|C|$]]|$1|O|3|P|5|F|7|1H|8|@]|9|@]|C|$G|H]]|$1|Q|3|R|5|6|7|1I|8|@]|9|@$A|1J|B|1K|1|1L]]|C|$]]|$1|S|3|T|5|6|7|1M|8|@$A|1N|B|1O|U|V]|$A|1P|B|1Q|U|V]|$A|1R|B|1S|U|V]]|9|@]|C|$]]|$1|W|3|X|5|F|7|1T|8|@]|9|@]|C|$G|H]]|$1|Y|3|-4|5|6|7|1U|8|@]|9|@]|C|$]]]|Z|$10|$5|11|12|13|C|$14|15]]|16|$5|11|12|13|C|$14|17]]]]

While searching for a solution to this problem, I found a variation on GONeale's answer through <a href="http://patrickdesjardins.com/blog/how-to-update-specific-field-of-your-entity-with-a-generic-method-and-entity-framework" rel="noreferrer">Patrick Desjardins' blog</a>:

<pre><code>public int Update(T entity, Expression&lt;Func&lt;T, object&gt;&gt;[] properties)
{
 DatabaseContext.Entry(entity).State = EntityState.Unchanged;
 foreach (var property in properties)
 {
 var propertyName = ExpressionHelper.GetExpressionText(property);
 DatabaseContext.Entry(entity).Property(propertyName).IsModified = true;
 }
 return DatabaseContext.SaveChangesWithoutValidation();
}
</code></pre>

<blockquote>
 "As you can see, it takes as its second parameter an expression of a
 function. This will let use this method by specifying in a Lambda
 expression which property to update."
</blockquote>

<pre><code>...Update(Model, d=&gt;d.Name);
//or
...Update(Model, d=&gt;d.Name, d=&gt;d.SecondProperty, d=&gt;d.AndSoOn);
</code></pre>

( A somewhat similar solution is also given here: <a href="https://stackoverflow.com/a/5749469/2115384">https://stackoverflow.com/a/5749469/2115384</a> )

The method I am currently using in my own code, extended to handle also (Linq) Expressions of type <code>ExpressionType.Convert</code>. This was necessary in my case, for example with <code>Guid</code> and other object properties. Those were 'wrapped' in a Convert() and therefore not handled by <code>System.Web.Mvc.ExpressionHelper.GetExpressionText</code>.

<pre><code>public int Update(T entity, Expression&lt;Func&lt;T, object&gt;&gt;[] properties)
{
 DbEntityEntry&lt;T&gt; entry = dataContext.Entry(entity);
 entry.State = EntityState.Unchanged;
 foreach (var property in properties)
 {
 string propertyName = "";
 Expression bodyExpression = property.Body;
 if (bodyExpression.NodeType == ExpressionType.Convert &amp;&amp; bodyExpression is UnaryExpression)
 {
 Expression operand = ((UnaryExpression)property.Body).Operand;
 propertyName = ((MemberExpression)operand).Member.Name;
 }
 else
 {
 propertyName = System.Web.Mvc.ExpressionHelper.GetExpressionText(property);
 }
 entry.Property(propertyName).IsModified = true;
 }

 dataContext.Configuration.ValidateOnSaveEnabled = false;
 return dataContext.SaveChanges();
}
</code></pre>

blocks|key|3024238|text|public+void+ChangePassword(int+userId,+string+password)
{
++var+user+=+new+User{+Id+=+userId,+Password+=+password+};
++using+(var+db+=+new+DbContextName())
++{
++++db.Entry(user).State+=+EntityState.Added;
++++db.SaveChanges();
++}
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|3024239|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>public void ChangePassword(int userId, string password)
{
 var user = new User{ Id = userId, Password = password };
 using (var db = new DbContextName())
 {
 db.Entry(user).State = EntityState.Added;
 db.SaveChanges();
 }
}
</code></pre>

blocks|key|297950|text|我知道这是一个老帖子，但我也在寻找类似的解决方案，并决定使用@Doku-so提供的解决方案。我的评论是为了回答@Imran+Rizvi提出的问题，我关注了@Doku-so链接，该链接显示了类似的实现。@Imran+Rizvi的问题是，他在使用提供的解决方案时遇到错误：“无法将Lambda表达式转换为类型”Expression>+[]“，因为它不是委托类型”。我想提供我对@Doku-so的解决方案所做的一个小修改，以修复这个错误，以防其他人在看到这篇文章时决定使用@Doku-so的解决方案。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|297951|这个问题是Update方法中的第二个参数，|297952|public+int+Update(T+entity,+Expression<Func<T,+object>>[]+properties).+|code-block|syntax|javascript|297953|要使用提供的语法调用此方法...|297954|Update(Model,+d=>d.Name,+d=>d.SecondProperty,+d=>d.AndSoOn);+|297955|因此，您必须在第二个arugment之前添加'params‘关键字。|297956|public+int+Update(T+entity,+params+Expression<Func<T,+object>>[]+properties)|297957|或者，如果您不想更改方法签名，那么要调用更新方法，您需要添加“new”关键字，指定数组的大小，最后使用集合对象初始化器语法对每个属性进行更新，如下所示。|offset|length|style|BOLD|297958|Update(Model,+new+Expression<Func<T,+object>>[3]+{+d=>d.Name+},+{+d=>d.SecondProperty+},+{+d=>d.AndSoOn+});|297959|在@Doku-+so的示例中，他指定了一个表达式数组，因此您必须在数组中传递要更新的属性，由于数组的原因，您还必须指定数组的大小。为了避免这种情况，您还可以将表达式参数更改为使用IEnumerable而不是数组。|297960|这是我的@Doku-so解决方案的实现。|297961|public+int+Update<TEntity>(LcmsEntities+dataContext,+DbEntityEntry<TEntity>+entityEntry,+params+Expression<Func<TEntity,+object>>[]+properties)
+++++where+TEntity:+class
++++{
++++++++entityEntry.State+=+System.Data.Entity.EntityState.Unchanged;

++++++++properties.ToList()
++++++++++++.ForEach((property)+=>
++++++++++++{
++++++++++++++++var+propertyName+=+string.Empty;
++++++++++++++++var+bodyExpression+=+property.Body;
++++++++++++++++if+(bodyExpression.NodeType+==+ExpressionType.Convert
++++++++++++++++++++&&+bodyExpression+is+UnaryExpression)
++++++++++++++++{
++++++++++++++++++++Expression+operand+=+((UnaryExpression)property.Body).Operand;
++++++++++++++++++++propertyName+=+((MemberExpression)operand).Member.Name;
++++++++++++++++}
++++++++++++++++else
++++++++++++++++{
++++++++++++++++++++propertyName+=+System.Web.Mvc.ExpressionHelper.GetExpressionText(property);
++++++++++++++++}

++++++++++++++++entityEntry.Property(propertyName).IsModified+=+true;
++++++++++++});

++++++++dataContext.Configuration.ValidateOnSaveEnabled+=+false;

++++++++return+dataContext.SaveChanges();
++++}|297962|使用：|297963|this.Update<Contact>(context,+context.Entry(modifiedContact),+c+=>+c.Active,+c+=>+c.ContactTypeId);|297964|@Doku-so提供了一个使用generic的很酷的方法，我使用了这个概念来解决我的问题，但你就是不能使用@Doku-so的解决方案，而且在这篇文章和链接的文章中都没有人回答使用错误的问题。|297965|entityMap^0|0|0|0|0|0|0|0|V|3|0|0|0|0|0|0|3|0|0|0^^$0|@$1|2|3|4|5|6|7|1C|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1D|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|1E|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|1F|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|1G|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|1H|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|1I|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|1J|8|@$S|1K|T|1L|U|V]]|9|@]|A|$]]|$1|W|3|X|5|F|7|1M|8|@]|9|@]|A|$G|H]]|$1|Y|3|Z|5|6|7|1N|8|@]|9|@]|A|$]]|$1|10|3|11|5|6|7|1O|8|@]|9|@]|A|$]]|$1|12|3|13|5|F|7|1P|8|@]|9|@]|A|$G|H]]|$1|14|3|15|5|6|7|1Q|8|@$S|1R|T|1S|U|V]]|9|@]|A|$]]|$1|16|3|17|5|F|7|1T|8|@]|9|@]|A|$G|H]]|$1|18|3|19|5|6|7|1U|8|@]|9|@]|A|$]]|$1|1A|3|-4|5|6|7|1V|8|@]|9|@]|A|$]]]|1B|$]]

I know this is an old thread but I was also looking for a similar solution and decided to go with the solution @Doku-so provided. I'm commenting to answer the question asked by @Imran Rizvi , I followed @Doku-so link that shows a similar implementation. @Imran Rizvi's question was that he was getting an error using the provided solution 'Cannot convert Lambda expression to Type 'Expression> [] ' because it is not a delegate type'. I wanted to offer a small modification I made to @Doku-so's solution that fixes this error in case anyone else comes across this post and decides to use @Doku-so's solution.

The issue is the second argument in the Update method, 

<pre><code>public int Update(T entity, Expression&lt;Func&lt;T, object&gt;&gt;[] properties). 
</code></pre>

To call this method using the syntax provided...

<pre><code>Update(Model, d=&gt;d.Name, d=&gt;d.SecondProperty, d=&gt;d.AndSoOn); 
</code></pre>

You must add the 'params' keyword in front of the second arugment as so.

<pre><code>public int Update(T entity, params Expression&lt;Func&lt;T, object&gt;&gt;[] properties)
</code></pre>

or if you don't want to change the method signature then to call the Update method you need to add the 'new' keyword, specify the size of the array, then finally use the collection object initializer syntax for each property to update as seen below.

<pre><code>Update(Model, new Expression&lt;Func&lt;T, object&gt;&gt;[3] { d=&gt;d.Name }, { d=&gt;d.SecondProperty }, { d=&gt;d.AndSoOn });
</code></pre>

In @Doku-so's example he is specifying an array of Expressions so you must pass the properties to update in an array, because of the array you must also specify the size of the array. To avoid this you could also change the expression argument to use IEnumerable instead of an array.

Here is my implementation of @Doku-so's solution.

<pre><code>public int Update&lt;TEntity&gt;(LcmsEntities dataContext, DbEntityEntry&lt;TEntity&gt; entityEntry, params Expression&lt;Func&lt;TEntity, object&gt;&gt;[] properties)
 where TEntity: class
 {
 entityEntry.State = System.Data.Entity.EntityState.Unchanged;

 properties.ToList()
 .ForEach((property) =&gt;
 {
 var propertyName = string.Empty;
 var bodyExpression = property.Body;
 if (bodyExpression.NodeType == ExpressionType.Convert
 &amp;&amp; bodyExpression is UnaryExpression)
 {
 Expression operand = ((UnaryExpression)property.Body).Operand;
 propertyName = ((MemberExpression)operand).Member.Name;
 }
 else
 {
 propertyName = System.Web.Mvc.ExpressionHelper.GetExpressionText(property);
 }

 entityEntry.Property(propertyName).IsModified = true;
 });

 dataContext.Configuration.ValidateOnSaveEnabled = false;

 return dataContext.SaveChanges();
 }
</code></pre>

Usage: 

<pre><code>this.Update&lt;Contact&gt;(context, context.Entry(modifiedContact), c =&gt; c.Active, c =&gt; c.ContactTypeId);
</code></pre>

@Doku-so provided a cool approach using generic's, I used the concept to solve my issue but you just can't use @Doku-so's solution as is and in both this post and the linked post no one answered the usage error questions.

blocks|key|298464|text|结合几个建议，我提出了以下建议：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|298465|++++async+Task<bool>+UpdateDbEntryAsync<T>(T+entity,+params+Expression<Func<T,+object>>[]+properties)+where+T+:+class
++++{
++++++++try
++++++++{
++++++++++++var+entry+=+db.Entry(entity);
++++++++++++db.Set<T>().Attach(entity);
++++++++++++foreach+(var+property+in+properties)
++++++++++++++++entry.Property(property).IsModified+=+true;
++++++++++++await+db.SaveChangesAsync();
++++++++++++return+true;
++++++++}
++++++++catch+(Exception+ex)
++++++++{
++++++++++++System.Diagnostics.Debug.WriteLine("UpdateDbEntryAsync+exception:+"+%2B+ex.Message);
++++++++++++return+false;
++++++++}+
++++}|code-block|syntax|javascript|298466|调用者|298467|UpdateDbEntryAsync(dbc,+d+=>+d.Property1);//,+d+=>+d.Property2,+d+=>+d.Property3,+etc.+etc.);|298468|或通过|298469|await+UpdateDbEntryAsync(dbc,+d+=>+d.Property1);|298470|298471|bool+b+=+UpdateDbEntryAsync(dbc,+d+=>+d.Property1).Result;|298472|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|U|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|V|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|W|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|X|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|O|3|L|5|6|7|Z|8|@]|9|@]|A|$]]|$1|P|3|Q|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|R|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|S|$]]

Combining several suggestions I propose the following: 

<pre><code> async Task&lt;bool&gt; UpdateDbEntryAsync&lt;T&gt;(T entity, params Expression&lt;Func&lt;T, object&gt;&gt;[] properties) where T : class
 {
 try
 {
 var entry = db.Entry(entity);
 db.Set&lt;T&gt;().Attach(entity);
 foreach (var property in properties)
 entry.Property(property).IsModified = true;
 await db.SaveChangesAsync();
 return true;
 }
 catch (Exception ex)
 {
 System.Diagnostics.Debug.WriteLine("UpdateDbEntryAsync exception: " + ex.Message);
 return false;
 } 
 }
</code></pre>

called by 

<pre><code>UpdateDbEntryAsync(dbc, d =&gt; d.Property1);//, d =&gt; d.Property2, d =&gt; d.Property3, etc. etc.);
</code></pre>

Or by 

<pre><code>await UpdateDbEntryAsync(dbc, d =&gt; d.Property1);
</code></pre>

Or by 

<pre><code>bool b = UpdateDbEntryAsync(dbc, d =&gt; d.Property1).Result;
</code></pre>

blocks|key|3024305|text|我使用ValueInjecter+nuget将绑定模型注入到数据库实体中，方法如下：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3024306|public+async+Task<IHttpActionResult>+Add(CustomBindingModel+model)
{
+++var+entity=+await+db.MyEntities.FindAsync(model.Id);
+++if+(entity==+null)+return+NotFound();

+++entity.InjectFrom<NoNullsInjection>(model);

+++await+db.SaveChangesAsync();
+++return+Ok();
}|code-block|syntax|javascript|3024307|注意自定义约定的用法，如果来自服务器的属性为空，则不会更新这些属性。|3024308|ValueInjecter+v3%2B|3024309|public+class+NoNullsInjection+:+LoopInjection
{
++++protected+override+void+SetValue(object+source,+object+target,+PropertyInfo+sp,+PropertyInfo+tp)
++++{
++++++++if+(sp.GetValue(source)+==+null)+return;
++++++++base.SetValue(source,+target,+sp,+tp);
++++}
}|3024310|用法：|3024311|target.InjectFrom<NoNullsInjection>(source);|3024312|值注入器V2|3024313|查找this+answer|3024314|注意事项|3024315|您不会知道该属性是否被故意清除为空，或者它只是没有任何值。换句话说，该属性值只能替换为另一个值，而不能清除。|3024316|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/23696060/80434^0|3|D|0|0|0|0|0|0|0|0|2|B|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1A|8|@$9|1B|A|1C|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|1D|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1E|8|@]|D|@]|E|$]]|$1|M|3|N|5|6|7|1F|8|@]|D|@]|E|$]]|$1|O|3|P|5|H|7|1G|8|@]|D|@]|E|$I|J]]|$1|Q|3|R|5|6|7|1H|8|@]|D|@]|E|$]]|$1|S|3|T|5|H|7|1I|8|@]|D|@]|E|$I|J]]|$1|U|3|V|5|6|7|1J|8|@]|D|@]|E|$]]|$1|W|3|X|5|6|7|1K|8|@]|D|@$9|1L|A|1M|1|1N]]|E|$]]|$1|Y|3|Z|5|6|7|1O|8|@]|D|@]|E|$]]|$1|10|3|11|5|6|7|1P|8|@]|D|@]|E|$]]|$1|12|3|-4|5|6|7|1Q|8|@]|D|@]|E|$]]]|13|$14|$5|15|16|17|E|$18|19]]]]

I use <code>ValueInjecter</code> nuget to inject Binding Model into database Entity using following:

<pre><code>public async Task&lt;IHttpActionResult&gt; Add(CustomBindingModel model)
{
 var entity= await db.MyEntities.FindAsync(model.Id);
 if (entity== null) return NotFound();

 entity.InjectFrom&lt;NoNullsInjection&gt;(model);

 await db.SaveChangesAsync();
 return Ok();
}
</code></pre>

Notice the usage of custom convention that doesn't update Properties if they're null from server. 

<h2>ValueInjecter v3+</h2>

<pre><code>public class NoNullsInjection : LoopInjection
{
 protected override void SetValue(object source, object target, PropertyInfo sp, PropertyInfo tp)
 {
 if (sp.GetValue(source) == null) return;
 base.SetValue(source, target, sp, tp);
 }
}
</code></pre>

Usage:

<pre><code>target.InjectFrom&lt;NoNullsInjection&gt;(source);
</code></pre>

<h2>Value Injecter V2</h2>

Lookup <a href="https://stackoverflow.com/a/23696060/80434">this answer</a> 

<h2>Caveat</h2>

You won't know whether the property is intentionally cleared to null OR it just didn't have any value it. In other words, the property value can only be replaced with another value but not cleared.

blocks|key|295440|text|在实体框架核心中，Attach返回条目，因此您所需要的是：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|295441|var+user+=+new+User+{+Id+=+userId,+Password+=+password+};
db.Users.Attach(user).Property(x+=>+x.Password).IsModified+=+true;
db.SaveChanges();|code-block|syntax|javascript|295442|entityMap^0|9|6|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

In Entity Framework Core, <code>Attach</code> returns the entry, so all you need is:

<pre class="lang-csharp prettyprint-override"><code>var user = new User { Id = userId, Password = password };
db.Users.Attach(user).Property(x =&gt; x.Password).IsModified = true;
db.SaveChanges();
</code></pre>

blocks|key|3238717|text|实体框架跟踪您对通过DbContext从数据库查询的对象所做的更改。例如，如果您的DbContext实例名称为dbContext|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3238718|public+void+ChangePassword(int+userId,+string+password){
+++++var+user+=+dbContext.Users.FirstOrDefault(u=>u.UserId+==+userId);
+++++user.password+=+password;
+++++dbContext.SaveChanges();
}|code-block|syntax|javascript|3238719|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Entity framework tracks your changes on objects that you queried from database via DbContext. For example if you DbContext instance name is dbContext

<pre><code>public void ChangePassword(int userId, string password){
 var user = dbContext.Users.FirstOrDefault(u=&gt;u.UserId == userId);
 user.password = password;
 dbContext.SaveChanges();
}
</code></pre>

blocks|key|3238728|text|public+async+Task<bool>+UpdateDbEntryAsync(TEntity+entity,+params+Expression<Func<TEntity,+object>>[]+properties)
{
++++try
++++{
++++++++this.Context.Set<TEntity>().Attach(entity);
++++++++EntityEntry<TEntity>+entry+=+this.Context.Entry(entity);
++++++++entry.State+=+EntityState.Modified;
++++++++foreach+(var+property+in+properties)
++++++++++++entry.Property(property).IsModified+=+true;
++++++++await+this.Context.SaveChangesAsync();
++++++++return+true;
++++}
++++catch+(Exception+ex)
++++{
++++++++throw+ex;
++++}
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|3238729|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>public async Task&lt;bool&gt; UpdateDbEntryAsync(TEntity entity, params Expression&lt;Func&lt;TEntity, object&gt;&gt;[] properties)
{
 try
 {
 this.Context.Set&lt;TEntity&gt;().Attach(entity);
 EntityEntry&lt;TEntity&gt; entry = this.Context.Entry(entity);
 entry.State = EntityState.Modified;
 foreach (var property in properties)
 entry.Property(property).IsModified = true;
 await this.Context.SaveChangesAsync();
 return true;
 }
 catch (Exception ex)
 {
 throw ex;
 }
}
</code></pre>

blocks|key|3238743|text|我也在寻找同样的东西，最后我找到了解决方案|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3238744|using+(CString+conn+=+new+CString())
{
++++USER+user+=+conn.USERs.Find(CMN.CurrentUser.ID);
++++user.PASSWORD+=+txtPass.Text;
++++conn.SaveChanges();
}|code-block|syntax|javascript|3238745|相信我，它对我来说就像一个护身符。|3238746|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I was looking for same and finally I found the solution

<pre><code>using (CString conn = new CString())
{
 USER user = conn.USERs.Find(CMN.CurrentUser.ID);
 user.PASSWORD = txtPass.Text;
 conn.SaveChanges();
}
</code></pre>

believe me it work for me like a charm.

blocks|key|300713|text|在EntityFramework+Core2.x中，不需要Attach|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|300714|+//+get+a+tracked+entity
+var+entity+=+context.User.Find(userId);
+entity.someProp+=+someValue;
+//+other+property+changes+might+come+here
+context.SaveChanges();|code-block|syntax|javascript|300715|在SQL+Server中尝试了此操作，并对其进行了分析：|300716|exec+sp_executesql+N'SET+NOCOUNT+ON;
UPDATE+[User]+SET+[someProp]+=+@p0
WHERE+[UserId]+=+@p1;
SELECT+@@ROWCOUNT;

',N'@p1+int,@p0+bit',@p1=1223424,@p0=1|300717|查找可确保已加载的实体不会触发SELECT，如果需要，还会自动附加实体(从文档)：|300718|++++///+++++Finds+an+entity+with+the+given+primary+key+values.+If+an+entity+with+the+given+primary+key+values
++++///+++++is+being+tracked+by+the+context,+then+it+is+returned+immediately+without+making+a+request+to+the
++++///+++++database.+Otherwise,+a+query+is+made+to+the+database+for+an+entity+with+the+given+primary+key+values
++++///+++++and+this+entity,+if+found,+is+attached+to+the+context+and+returned.+If+no+entity+is+found,+then
++++///+++++null+is+returned.|300719|entityMap^0|T|6|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|Y|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|10|8|@]|D|@]|E|$]]|$1|Q|3|R|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|S|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|T|$]]

In EntityFramework Core 2.x there is no need for <code>Attach</code>:

<pre><code> // get a tracked entity
 var entity = context.User.Find(userId);
 entity.someProp = someValue;
 // other property changes might come here
 context.SaveChanges();
</code></pre>

Tried this in SQL Server and profiling it:

<pre><code>exec sp_executesql N'SET NOCOUNT ON;
UPDATE [User] SET [someProp] = @p0
WHERE [UserId] = @p1;
SELECT @@ROWCOUNT;

',N'@p1 int,@p0 bit',@p1=1223424,@p0=1
</code></pre>

Find ensures that already loaded entities do not trigger a SELECT and also automatically attaches the entity if needed (from the docs):

<pre><code> /// Finds an entity with the given primary key values. If an entity with the given primary key values
 /// is being tracked by the context, then it is returned immediately without making a request to the
 /// database. Otherwise, a query is made to the database for an entity with the given primary key values
 /// and this entity, if found, is attached to the context and returned. If no entity is found, then
 /// null is returned.
</code></pre>

blocks|key|295479|text|_context.Users.UpdateProperty(p+=>+p.Id,+request.UserId,+new+UpdateWrapper<User>()
++++++++++++++++{
++++++++++++++++++++Expression+=+p+=>+p.FcmId,Value+=+request.FcmId
++++++++++++++++});
+++await+_context.SaveChangesAsync(cancellationToken);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|295480|更新属性是一个扩展方法|unstyled|295481|public+static+void+UpdateProperty<T,+T2>(this+DbSet<T>+set,+Expression<Func<T,+T2>>+idExpression,
++++++++++++T2+idValue,
++++++++++++params+UpdateWrapper<T>[]+updateValues)
++++++++++++where+T+:+class,+new()
++++++++{
++++++++++++var+entity+=+new+T();
++++++++++++var+attach+=+set.Attach(entity);
++++++++++++attach.Property(idExpression).IsModified+=+false;
++++++++++++attach.Property(idExpression).OriginalValue+=+idValue;
++++++++++++foreach+(var+update+in+updateValues)
++++++++++++{
++++++++++++++++attach.Property(update.Expression).IsModified+=+true;
++++++++++++++++attach.Property(update.Expression).CurrentValue+=+update.Value;
++++++++++++}
++++++++}|295482|Update+Wrapper是一个类|295483|public+class+UpdateWrapper<T>
++++{
++++++++public+Expression<Func<T,+object>>+Expression++{+get;+set;+}
++++++++public+object+Value+{+get;+set;+}
++++}|295484|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|P|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$B|C]]|$1|I|3|J|5|F|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$B|C]]|$1|M|3|-4|5|F|7|T|8|@]|9|@]|A|$]]]|N|$]]

<pre><code>_context.Users.UpdateProperty(p =&gt; p.Id, request.UserId, new UpdateWrapper&lt;User&gt;()
 {
 Expression = p =&gt; p.FcmId,Value = request.FcmId
 });
 await _context.SaveChangesAsync(cancellationToken);
</code></pre>
Update Property is an extension method
<pre><code>public static void UpdateProperty&lt;T, T2&gt;(this DbSet&lt;T&gt; set, Expression&lt;Func&lt;T, T2&gt;&gt; idExpression,
 T2 idValue,
 params UpdateWrapper&lt;T&gt;[] updateValues)
 where T : class, new()
 {
 var entity = new T();
 var attach = set.Attach(entity);
 attach.Property(idExpression).IsModified = false;
 attach.Property(idExpression).OriginalValue = idValue;
 foreach (var update in updateValues)
 {
 attach.Property(update.Expression).IsModified = true;
 attach.Property(update.Expression).CurrentValue = update.Value;
 }
 }
</code></pre>
And Update Wrapper is a class
<pre><code>public class UpdateWrapper&lt;T&gt;
 {
 public Expression&lt;Func&lt;T, object&gt;&gt; Expression { get; set; }
 public object Value { get; set; }
 }
</code></pre>

Here's the table

Users

<pre><code>UserId
UserName
Password
EmailAddress
</code></pre>

and the code..

<pre class="lang-csharp prettyprint-override"><code>public void ChangePassword(int userId, string password){
//code to update the password..
}
</code></pre>

How to update only one field using Entity Framework?

数据存储

SQL Server

数据库

服务器

这是桌子用户UserIdUserNamePasswordEmailAddress和代码..public void ChangePassword(int userId, string password){//code to update the password..}

问如何使用Entity Framework只更新一个字段？
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