如何减少获得此结果所需的查询数

Question

I'm writing an application on top of CodeIgniter to better organize my ebook collection. I'm nearly done, but I realize my 'browse' page is running far too many queries - two per book - to get their information. Obviously not at all ideal, especially since I have about 1000 books to put into this system.

I currently have one model function which gets all of the books (will eventually be modified to take parameters - that's the next step) and another that gets the meta information for each returned book. The second function is the one which makes two queries for each book - one to get the information in the book table and another to get the tags associated with the book. Here are the two model functions:

Get the list of books:

function get_books() {
    $this->db->select('isbn')->order_by('title');
    $query = $this->db->get('books');
    $result = $query->result();
    return $result;
}

Get the book meta information:

function get_book_info($isbn) {
    // Grab the book from Amazon
    $amazon = $this->amazon->get_amazon_item($isbn);

    // Get the book info
    $this->db->select('title, publisher, date, thumb, filename, pages');
    $query = $this->db->get_where('books', array('isbn' => $isbn));
    $bookResult = $query->row();

    // Get the book's tags
    $this->db->select('tag');
    $this->db->from('tags AS t');
    $this->db->join('books_tags AS bt', 'bt.tag_id = t.id', 'left');
    $this->db->where('bt.book_id', $isbn);
    $this->db->order_by('t.tag');
    $tagQuery = $this->db->get();
    foreach ($tagQuery->result() as $row) {
        $tagResult[] = $row->tag;
    }
    $tagResult = implode(', ', $tagResult);

    // Send data
    $data = array(
        'isbn' => $isbn,
        'thumb' => $bookResult->thumb,
        'title' => strip_slashes($bookResult->title),
        'file' => $bookResult->filename,
        'publisher' => strip_slashes($bookResult->publisher),
        'date' => date('F j, Y', strtotime($bookResult->date)),
        'pages' => $bookResult->pages,
        'tags' => $tagResult,
        'rating' => $amazon->Items->Item->CustomerReviews->AverageRating,
        'raters' => $amazon->Items->Item->CustomerReviews->TotalReviews
    );
    return $data;
}

I'm certain there's a way to write one or two queries that will gather all the records into objects I can then filter through, rather than having to write two queries for each one, but I have no idea where to even start trying to write that. Any suggestions are welcome.

Thanks much, Marcus

Answer 1

With some help from this topic and in others in creating a better query, I was able to resolve this with the following code:

function get_book_info() {

    /*
     * SELECT b.isbn, b.title, b.publisher, b.date, b.thumb, b.filename, b.pages, t.tag
     * FROM books AS b
     * INNER JOIN books_tags AS bt ON b.isbn = bt.book_id
     * INNER JOIN tags AS t ON bt.tag_id = t.id
     * ORDER BY b.title, t.tag
     */

    $this->db->select('b.isbn, b.title, b.publisher, b.date, b.thumb, b.filename, b.pages, t.tag');
    $this->db->from('books AS b');
    $this->db->join('books_tags AS bt', 'b.isbn = bt.book_id', 'inner');
    $this->db->join('tags AS t', 'bt.tag_id = t.id', 'inner');
    $this->db->order_by('b.title, t.tag');
    $query = $this->db->get();
    $result = $query->result();

    $counter = '';
    $record = $meta = $tags = array();
    $count = count($result);
    $i = 1;

    foreach ($result as $book) {
        // If this is not the last row
        if ($i < $count) {
            // If this is the first appearance of this book
            if ($counter != $book->isbn) {
                // If the meta array already exists
                if ($meta) {
                    // Add the combined tag string to the meta array
                    $meta['tags'] = implode(', ', $tags);
                    // Add the meta array
                    $record[] = $meta;
                    // Empty the tags array
                    $tags = array();
                }
                // Reset the counter
                $counter = $book->isbn;
                // Grab the book from Amazon
                $amazon = $this->amazon->get_amazon_item($book->isbn);
                // Collect the book information
                $meta = array(
                    'isbn' => $book->isbn,
                    'title' => strip_slashes($book->title),
                    'publisher' => strip_slashes($book->publisher),
                    'date' => date('F j, Y', strtotime($book->date)),
                    'thumb' => $book->thumb,
                    'file' => $book->filename,
                    'pages' => $book->pages,
                    'rating' => $amazon->Items->Item->CustomerReviews->AverageRating,
                    'raters' => $amazon->Items->Item->CustomerReviews->TotalReviews
                );
                // Add the tag to the tags array
                $tags[] = $book->tag;
            } else {
                // All we need is the tag
                $tags[] = $book->tag;
            }
        // If this is the last row
        } else {
            // If this is the first appearance of this book
            if ($counter != $book->isbn) {
                // Grab the book from Amazon
                $amazon = $this->amazon->get_amazon_item($book->isbn);
                // Collect the book information
                $meta = array(
                    'isbn' => $book->isbn,
                    'title' => strip_slashes($book->title),
                    'publisher' => strip_slashes($book->publisher),
                    'date' => date('F j, Y', strtotime($book->date)),
                    'thumb' => $book->thumb,
                    'file' => $book->filename,
                    'pages' => $book->pages,
                    'rating' => $amazon->Items->Item->CustomerReviews->AverageRating,
                    'raters' => $amazon->Items->Item->CustomerReviews->TotalReviews
                );
                // Add the tag to the tags array
                $tags[] = $book->tag;
                // Add the combined tag string to the meta array
                $meta['tags'] = implode(', ', $tags);
                // Add the meta array
                $record[] = $meta;
            } else {
                // All we need is the tag
                $tags[] = $book->tag;
                // Add the combined tag string to the meta array
                $meta['tags'] = implode(', ', $tags);
                // Add the meta array
                $record[] = $meta;
            }
        }
        $i++;
    }

    return $record;
}

There may very well be a better way to handle this, but this was how my logic saw it. And only one query, total.