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Many To Many. Find by field in 'through' table
  • Let's say I have Model_Post and it has many and belongs to many Model_Tag`s. 
    I need to find posts that have a tag with id 1.
    Now I do this like that:

    $posts = Model_Post::query()->related('tags')->where('t1_through.tag_id', 1)->get();

    It looked like a (not very good) solution, until i noticed, that $post->tags gives me only one tag (fair enough)
    Like a temporary solution I walk through posts, write their ids into the $ids array and then use another query with where('id', 'IN', $ids) statement.

    I have two questions: 
    * Is there a more correct way to find posts by a tag
    * if there isn't, does ORM support something like Post.includes(:tags) (generating 2 DB queries) like rails activerecord does?

    PS: I did try to find this in these forums but I failed.
    PPS: sorry for my bad English
    PPPS: Fuel is awesome.
  • HarroHarro
    Accepted Answer
    You should be able to just use

    where('', '=', 1)

    in your query. It's obvious it gives you only one tag, you select it on primary key, so there can only be one.

    If you need posts for a tag, you need to run your query the other way around:

    $tag = Model_Tags::query()->related('posts')->where('id,'=',1)->get();
  • get() did not work for me, i think, it should be get_one() ?

    I have been thinking about quering the Model_Tag BUT. If i do so I think i won't be able to limit() and offset().
    Also, this query was not meant just to select posts by tag. I wanted to make it combined with search by title. I used to do it that way:

    $posts = Model_Post::query()->related('tags');
    strlen($q) > 2 && $posts = $posts->where('name', 'LIKE', '%'.$q.'%');
    isset($tag) && $posts = $posts->where('', $tag);
    $posts = $posts->get();

    But if i run the query from Model_Tag it becomes impossible to get posts by title if $tag is not set,

    Thanks for your instant response BTW.
  • difference between get() and get_one() is that the first returns an array of results (always, also if there is only one), and the second adds a LIMIT 1, and always returns a single result (or null if none found).

    If you have multiple criteria, I assume you want or_where()? adding additional where() would add an AND, and I think you want an OR.

    If it is a many-to-many, you always have (possible) multiple results, no matter from which side you run the query. So it should always be get().
  • So can i limit() and offset() rows of joined table?
  • HarroHarro
    Accepted Answer
    You want to limit what exactly? You don't limit a specific table, you limit the result set of a query.

    ORM is designed to keep results consistent, so in a query that includes relations, by default it will either include a parent with all it's children, or not at all. But it will not include a partial result, a parent with some of it's children, because of a limit. This may cause a limit(10) to return more or less then 10 records, depending on how many children a parent has.

    If you don't want that, but are interested in a precise row limit (for example for paginating a table), you need to use rows_limit() and rows_offset() instead of limit() and offset().
  • I am sorry I couldn't explain well what i exactly want.

    I have a controller that gets posts performing filtering through posts, both by title and by tag_id. If both params are set then i want sql be with AND WHERE.

    I also have pagination on search results, so i will call limit() and offset() afterwards.
    now it's working like that:

    I have in post model a method:
    public static function search($q, $tag)
    $posts = Model_Post::query()->related('tags');
    strlen($q) > 2 && $posts = $posts->where('name', 'LIKE', '%'.$q.'%');
    isset($tag) && $posts = $posts->where('', $tag);
    $posts = $posts->get();

    $ids = array();

    foreach($posts as $post)
    $ids[] = $post->id;

    return Model_Post::query()->related('tags')
    ->where('id', 'IN', $ids);


    then i call in my controller
    $posts = Model_Post::search(Input::get('q'), Input::get('tag'))

    and pass $posts to my view

    I just wanted to ask how can i improve search method?
  • Why are you running the same query twice?

    The second one, with the id's, returns exactly the same records as the first one.
    public static function search($q, $tag)
    $posts = static::query()->related('tags');
    strlen($q) > 2 && $posts = $posts->where('name', 'LIKE', '%'.$q.'%');
    isset($tag) && $posts = $posts->where('', $tag);
    return $posts;
    This should work fine too.

    Note though that since you use related(), and you want pagination, you should call it like this:

    $posts = Model_Post::search(Input::get('q'), Input::get('tag'))
    otherwise you may not get the desired result, as ORM will retrieve complete posts->tags sets when you use limit().
  • I run the same query twice to have the complete list of related tags when $tag filter is set, as they will be passed and displayed in my view. otherwise it will obviously select only one tag with the specified id

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