PHP: Active record table joins

I have an app that uses the c开发者_如何学Goodeigniter CXTags tagging library.

The database structure is as follows:

posts

id

tags_ref

row_id

table

tag_id

tags

id

safe_tag

tag

My query basically goes if $safe_tag is not null then join tags_ref on post.id = tags_ref.row_id, join tags on tags_ref.tag_id = tags.id, where tags_ref.table = 'posts' and tags.safe_tag = 'food'

SELECT * FROM posts 
JOIN tags_ref ON posts.id = tags_ref.row_id
JOIN tags ON tags_ref.tag_id = tags.id
WHERE tags.safe_tag = $safe_id

Unfortunately the query I've written in active record is not functioning properly. The query works perfectly when £safe_tag is null but when it's not I get wrong results.

function get_posts($id = NULL, $safe_tag = NULL) {

    if($safe_tag != NULL){
        echo $safe_tag;//debugging
        $table = 'posts';
        $this->db->join('tags_ref', 'posts.id = tags_ref.row_id');
        $this->db->join('tags', 'tags_ref.tag_id = tags.id');
        $this->db->where('tags_ref.table', $table);
        $this->db->where('tags.safe_tag',$safe_tag);
    }

    //if an id was supplied
    if ( $id != NULL ) {
        $this->db->where('posts.city_id',$id);
    }

    // execute query
    $query = $this->db->get('posts');
    ...

Here is the query with profiling on:

SELECT *
FROM (`posts`)
INNER JOIN `tags_ref` ON `posts`.`id` = `tags_ref`.`row_id`
INNER JOIN `tags` ON `tags_ref`.`tag_id` = `tags`.`id`
WHERE `tags_ref`.`table` = 'posts'
AND `tags`.`safe_tag` = 'food'
AND `posts`.`city_id` = '2' 

Can someone have a look? I think I need a fresh set of eyes on it.

Your forgot to actually run the query inside your first if{}

if($safe_tag != NULL){
        echo $safe_tag;//debugging
        $table = 'posts';
        $this->db->join('tags_ref', 'posts.id = tags_ref.row_id');
        $this->db->join('tags', 'tags_ref.tag_id = tags.id');
        $this->db->where('tags_ref.table', $table);
        $this->db->where('tags.safe_tag',$safe_tag);
        $this->db->get(); // here 
    }