Question

我正在尝试获取记录的不同标签列表。除了标签名称总是第一个重复之外，它有点工作。

public EntityCollection<TagEntity> Tags
    {
        get
        {
            EntityCollection<TagEntity> x = new EntityCollection<TagEntity>()
           {
                new TagEntity(){Id=1, IsActive=true, Name="Tag1"},
                new TagEntity(){Id=2, IsActive=true, Name="Tag2"},
                new TagEntity(){Id=3, IsActive=true, Name="Tag3"},
                new TagEntity(){Id=4, IsActive=true, Name="Tag1"},
                new TagEntity(){Id=5, IsActive=true, Name="Tag5"},
                new TagEntity(){Id=6, IsActive=true, Name="Tag6"},
            };

            return x;
        }
    }

    public EntityCollection<StoryTagsEntity> StoryTags
    {
        get
        {
            EntityCollection<StoryTagsEntity> x = new EntityCollection<StoryTagsEntity>()
           {
                new StoryTagsEntity(){ TagId=1, StoryId=1},
                new StoryTagsEntity(){ TagId=1, StoryId=2},
                new StoryTagsEntity(){ TagId=2, StoryId=1},
                new StoryTagsEntity(){ TagId=3, StoryId=1},
                new StoryTagsEntity(){ TagId=2, StoryId=3},
                new StoryTagsEntity(){ TagId=4, StoryId=1},
            };

            return x;
        }
    }

    public List<string> FetchTagNamesByStory(bool? isActive, int StoryId)
    {
        var d = (from t in this.Tags
                 join st in this.StoryTags on t.Id equals st.StoryId
                 where t.IsActive == isActive.GetValueOrDefault() && st.StoryId == StoryId
                 select t.Name);

        List<string> x = new List<string>();

        foreach (var item in d)
        {
            x.Add(item);
        }

        return x;
    }

这会导致像这样的标签列表：

Tag1，Tag1，Tag1，Tag1

应该是：

标记1，标记2，标记3，标记1

有什么想法吗？

Answer 1

您将t.Id加入st.StoryId而不是st.TagId。如果你传入StoryId的1，你将永远得到Tag1。

Answer 2

你是对的，你的加入错了，你也可以做到以下几点：

public List<string> FetchTagNamesByStory(bool? isActive, int storyId)
{
    return (from t in Tags
        join st in StoryTags on t.Id equals st.TagId
        where t.IsActive == isActive.GetValueOrDefault() && st.StoryId == storyId
        select t.Name).ToList();
}

LINQ独特的连接查询

2 个答案: