我使用valueinjector nuget注入绑定模型到数据库实体使用如下:

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();
}

注意使用自定义约定，如果属性在服务器上为空，则不更新属性。

ValueInjecter v3 +

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);
    }
}

用法:

target.InjectFrom<NoNullsInjection>(source);

值注入器V2

查找这个答案

警告

您将不知道该属性是被故意清除为null还是它只是没有任何值。换句话说，属性值只能被替换为另一个值，而不能被清除。

在寻找这个问题的解决方案时，我在Patrick Desjardins的博客上找到了GONeale的答案:

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();
}

如你所见，它的第二个参数是a的表达式 函数。这将允许通过在Lambda中指定使用此方法 表示要更新哪个属性。”

...Update(Model, d=>d.Name);
//or
...Update(Model, d=>d.Name, d=>d.SecondProperty, d=>d.AndSoOn);

(这里也给出了一个类似的解决方案:https://stackoverflow.com/a/5749469/2115384)

我目前在自己的代码中使用的方法，扩展到处理类型ExpressionType.Convert的(Linq)表达式。这在我的例子中是必要的，例如Guid和其他对象属性。它们被“包装”在Convert()中，因此没有被System.Web.Mvc.ExpressionHelper.GetExpressionText处理。

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();
}

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.

问题是Update方法中的第二个参数，

public int Update(T entity, Expression<Func<T, object>>[] properties). 

使用提供的语法调用此方法…

Update(Model, d=>d.Name, d=>d.SecondProperty, d=>d.AndSoOn); 

你必须在第二个参数前面加上'params'关键字。

public int Update(T entity, params Expression<Func<T, object>>[] properties)

或者如果你不想改变方法签名，那么要调用Update方法，你需要添加'new'关键字，指定数组的大小，然后最后使用集合对象初始化语法来更新每个属性，如下所示。

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

在@Doku-so的例子中，他指定了一个表达式数组，所以你必须在数组中传递属性来更新，因为数组你还必须指定数组的大小。为了避免这种情况，您还可以更改表达式参数，使用IEnumerable而不是数组。

下面是@Doku-so解决方案的实现。

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();
    }

用法:

this.Update<Contact>(context, context.Entry(modifiedContact), c => c.Active, c => c.ContactTypeId);

@Doku-so提供了一种使用泛型的很酷的方法，我用这个概念来解决我的问题，但你不能使用@Doku-so的解决方案，在这篇文章和链接的帖子中，都没有人回答使用错误的问题。

_context.Users.UpdateProperty(p => p.Id, request.UserId, new UpdateWrapper<User>()
                {
                    Expression = p => p.FcmId,Value = request.FcmId
                });
   await _context.SaveChangesAsync(cancellationToken);

Update Property是一个扩展方法

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;
            }
        }

Update Wrapper是一个类

public class UpdateWrapper<T>
    {
        public Expression<Func<T, object>> Expression  { get; set; }
        public object Value { get; set; }
    }

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();
  }
}

Ladislav的答案更新为使用DbContext(在EF 4.1中引入):

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();
    }
}