如何返回 IEnumerable？

发布于 2024-10-30 02:03:33 字数 481 浏览 0 评论 0原文

我正在尝试返回 IEnumerable。这是我的代码：

public static IEnumerable<int> GetAnswersIDs(int id)
{
    using (var context = new MvcApplication4.Entity.test2Entities1())
    {
        return (from p in context.post
                  where p.post_parentid == id && p.post_isdeleted == false
                  select new
                  {
                      p.post_id
                  }).ToList();
    }           
}

是否可以返回 IEnumerable 对象？

原文

I am trying to return an IEnumerable. Here is my code:

public static IEnumerable<int> GetAnswersIDs(int id)
{
    using (var context = new MvcApplication4.Entity.test2Entities1())
    {
        return (from p in context.post
                  where p.post_parentid == id && p.post_isdeleted == false
                  select new
                  {
                      p.post_id
                  }).ToList();
    }           
}

Is it possible to return an IEnumerable object?

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樱花落人离去 2024-11-06 02:03:33

您不需要使用任何 To[Anything] 方法或类似的方法。你的错误是你选择的方式。正确的代码是这样的：

public static IEnumerable<int> GetAnswersIDs(int id)
{
    using (var context = new MvcApplication4.Entity.test2Entities1())
    {
        return (from p in context.post
                  where p.post_parentid == id && p.post_isdeleted == false
                  select p.post_id);
    }           
}

正如您所看到的，您创建了一个您不需要的匿名类，因为您只需要一个 int 值。

-- 编辑 --

您将面临 ObjectDispose 异常。因为当您使用返回的 IEnumerable 对象时，它需要使用 GetAnswersIDs 方法中配置的上下文。

因此，您可以返回一个 List 而不是 IEnumerable，或者您应该在 GetAnswersIDs 方法之外定义上下文。

这是带有列表的代码

public static List<int> GetAnswersIDs(int id)
{
    using (var context = new MvcApplication4.Entity.test2Entities1())
    {
        return (from p in context.post
                  where p.post_parentid == id && p.post_isdeleted == false
                  select p.post_id).ToList();
    }           
}

You dont need to use any To[Anything] method or something like that. Your mistake is your select way. The correct code is this:

public static IEnumerable<int> GetAnswersIDs(int id)
{
    using (var context = new MvcApplication4.Entity.test2Entities1())
    {
        return (from p in context.post
                  where p.post_parentid == id && p.post_isdeleted == false
                  select p.post_id);
    }           
}

As you see you created an anonymous class which you dont need because you want just an int value.

-- EDIT --

You will be faced to an ObjectDisposed Exception. Becase when you use the returned IEnumerable object it need to use the context which disposed in the GetAnswersIDs method.

So you could return a List instead of IEnumerable or you should define the context out of your GetAnswersIDs method.

This is the code with List

public static List<int> GetAnswersIDs(int id)
{
    using (var context = new MvcApplication4.Entity.test2Entities1())
    {
        return (from p in context.post
                  where p.post_parentid == id && p.post_isdeleted == false
                  select p.post_id).ToList();
    }           
}

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给我一枪 2024-11-06 02:03:33

我认为你应该使用 ToArray 或 ToList （Array 和 List 都实现 IEnumerable)，因为当您返回时，上下文已被释放，我几乎确定如果您使用 AsEnumerable 将枚举本身留给后续步骤，您会得到一个异常：

public static IEnumerable<int> GetAnswersIDs(int id)
{
    using (var context = new MvcApplication4.Entity.test2Entities1())
    {
        return (from p in context.post
                  where p.post_parentid == id && p.post_isdeleted == false
                  select p.post_id).ToArray();
    }           
}

BTW ，我认为在您的情况下，使用 linq 比非 linq 版本更详细：

public static IEnumerable<int> GetAnswersIDs(int id)
{
    using (var context = new MvcApplication4.Entity.test2Entities1())
    {
        return context.post.
          Where(p => p.post_parentid == id && !p.post_isdeleted).
          Select(p => p.post_id).
          ToArray();
    }           
}

作为旁注，您可能需要考虑重新格式化模型中的字段名称以满足 .NET 中的命名约定。

I think you should use ToArray or ToList (both Array<T> and List<T> implement IEnumerable<T>), since when you return, the context is disposed, I am nearly sure you will get an exception if you use AsEnumerable leaving the enumeration itself for later steps:

public static IEnumerable<int> GetAnswersIDs(int id)
{
    using (var context = new MvcApplication4.Entity.test2Entities1())
    {
        return (from p in context.post
                  where p.post_parentid == id && p.post_isdeleted == false
                  select p.post_id).ToArray();
    }           
}

BTW, I think in your case using linq is more verbose than the non-linq version:

public static IEnumerable<int> GetAnswersIDs(int id)
{
    using (var context = new MvcApplication4.Entity.test2Entities1())
    {
        return context.post.
          Where(p => p.post_parentid == id && !p.post_isdeleted).
          Select(p => p.post_id).
          ToArray();
    }           
}

As a side note, you might want to consider reformatting the field names in your model to meet the naming convensions in .NET.

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