实体框架跟踪您通过DbContext从数据库查询的对象的更改。例如，如果你的DbContext实例名是DbContext

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

我用这个:

实体:

public class Thing 
{
    [Key]
    public int Id { get; set; }
    public string Info { get; set; }
    public string OtherStuff { get; set; }
}

数据库上下文：

public class MyDataContext : DbContext
{
    public DbSet<Thing > Things { get; set; }
}

访问器代码:

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();

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。

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。

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;
    }
}

在EntityFramework Core 2中。x不需要附加:

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

尝试在SQL Server和分析它:

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

Find确保已经加载的实体不会触发SELECT，并在需要时自动附加实体(来自文档):

查找具有给定主键值的实体。如果上下文正在跟踪具有给定主键值的实体，则立即返回该实体，而无需向数据库发出请求。否则，将向数据库查询具有给定主键值的实体，如果找到该实体，则将该实体附加到上下文并返回。如果没有找到实体，则返回null。