标签系统的 linq 查询 - 搜索多个标签

问题描述

我有两张表，Tags(tagid, postid, tagname) 和 posts(postid, name, ...)
现在我想做一个查询，返回所有具有通用标签数量的帖子.比如:我想要所有带有标签 asp.net 和 jquery 的帖子

正如我所说，要查找的标签数量是通用的

我该怎么做?

谢谢

2009 年 11 月 17 日更新:有一个问题:表之间的关系不存在，因为我的主键在 2 个字段上(用于版本控制)我怎样才能使它没有关系?我正在使用 Linq To 实体

此外，查询应该具有良好的性能，并且不应发出数千个服务器请求.

我猜你不能在我遇到问题的 EF 3.5 中使用 .Contains().我通过使用这个WhereIn"扩展解决了这个问题

'Contains()' 使用 Linq to Entities 解决方法?p>

把它放到一个静态类中，然后你可以使用类似的东西:

IQueryablePostsWithByTags(IEnumerable<string> tagNames){var postIds = context.Tags.Select(t=>t.postid);foreach(tagNames 中的 var 标记){postIds = context.Tags.WhereIn(t=> t.postid, postIds).Where(t=>t.tagname == tag);}返回 context.Tags.Where(t=> t.posId, postIds)}

我真的认为你应该看看你的表之间的关系.

I have two tables, Tags(tagid, postid, tagname) and posts(postid, name, ...)
now i want to make a query that returns me all posts that have a generic amount of tags. like: i want all posts that have the tag asp.net AND jquery

as i said, the amount of tags to look for is generic

how can i do something like that?

thx

update 17.11.2009: there is one problem: the relation betwenn the tables does not exist, because my primary key is on 2 fields (for versioning) how can i make it without a relation? Im using Linq To Entities

also, the query should have good performance, and should not make thousands of server requests.

I guess you can't use .Contains() using EF 3.5 which I have had a problem with. I got around this by using this "WhereIn" extension

'Contains()' workaround using Linq to Entities?

put this into a static class then you could use something like:

IQueryable<Post> PostsWithByTags(IEnumerable<string> tagNames)
{
    var postIds = context.Tags.Select(t=>t.postid); 

    foreach (var tag in tagNames)
    {
       postIds = context.Tags
                     .WhereIn(t=> t.postid, postIds)
                     .Where(t=>t.tagname == tag);
    }

    return context.Tags.Where( t=> t.posId, postIds)
}

I really think you should look at having relationships between your tables though.

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