如何使用实体框架只更新一个字段?

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。

2015-02-25 01:02:33

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;
    }
}

2017-11-01 10:07:44

你基本上有两个选择:

一直用EF的方法，在这种情况下，你会根据提供的userId加载对象——整个对象都会被加载更新密码字段使用上下文的.SaveChanges()方法将对象保存回来

在这种情况下，具体如何处理就取决于EF了。我刚刚测试了这个，在这种情况下，我只改变一个对象的一个字段，EF创建的几乎是你手动创建的，太像:

`UPDATE dbo.Users SET Password = @Password WHERE UserId = @UserId`

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语句来处理实际上必要的更新。

你在T-SQL代码中定义了一个完全满足你需要的存储过程(只更新给定UserId的Password列，其他什么都不做——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，并且调用这个函数，而不是执行上面概述的步骤

2010-09-04 13:01:11

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();
  }
}

2014-01-09 04:13:54

在实体框架核心中，Attach返回条目，所以你所需要的是:

var user = new User { Id = userId, Password = password };
db.Users.Attach(user).Property(x => x.Password).IsModified = true;
db.SaveChanges();

2016-10-05 01:22:21

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.