CodeIgniter Active Record: Load One Row at a Time

问题:

The normal result() method described in the documentation appears to load all records immediately. My application needs to load about 30,000 rows, and one at a time, submit them to a third-party search index API. Obviously loading everything into memory at once doesn't work well (errors out because of too much memory).

So my question is, how can I achieve the effect of the conventional MySQLi API method, in which you load one row at a time in a loop?

回答1:

Here is something you can do.

while ($row = $result->_fetch_object()) {
  $data = array(
    'id'         => $row->id
    'some_value' => $row->some_field_name
  );
  // send row data to whatever api
  $this->send_data_to_api($data);
}

This will get one row at the time. Check the CodeIgniter source code, and you will see that they will do this when you execute the result() method.

回答2:

For those who want to save memory on large result-set:

Since CodeIgniter 3.0.0, There is a unbuffered_row function,

All the methods above will load the whole result into memory (prefetching). Use unbuffered_row() for processing large result sets.

 

This method returns a single result row without prefetching the whole result in memory as row() does. If your query has more than one row, it returns the current row and moves the internal data pointer ahead.

$query = $this->db->query("YOUR QUERY");

while ($row = $query->unbuffered_row())
{
    echo $row->title;
    echo $row->name;
    echo $row->body;
}

You can optionally pass ‘object’ (default) or ‘array’ in order to specify the returned value’s type:

$query->unbuffered_row();               // object
$query->unbuffered_row('object');       // object
$query->unbuffered_row('array');        // associative array

Official Document: https://www.codeigniter.com/userguide3/database/results.html#id2

回答3:

Well, there'se the row() method, which returns just one row as an object, or the row_array() method, which does the same but returns an array (of course).

So you could do something like

$sql = "SELECT * FROM yourtable";
$resultSet = $this->db->query($sql);
$total = $resultSet->num_rows();

for($i=0;$i<$total;$i++) {
  $row = $resultSet->row_array($i);
}

This fetches in a loop each row from the whole result set.
Which is about the same as fetching everyting and looping over the $this->db->query($sql)->result() method calls I believe.

If you want a row at a time either you make 30.000 calls, or you select all the results and fetch them one at a time or you fetch all and walk over the array. I can't see any way out now.

回答4:

Well, the thing is that result() gives away the entire reply of the query. row() simply fetches the first case and dumps the rest. However the query can still fetched 30 000 rows regardles of which function you use.

One design that would fit your cause would be:

$offset = (int)@$_GET['offset'];

$query = $this-db->query("SELECT * FROM table LIMIT ?, 1", array($offset));
$row = $query->row();

if ($row) {

    /* Run api with values */

    redirect(current_url().'?offset'.($offset + 1));

}

This would take one row, send it to api, update the page and use the next row. It will alos prevent the page from having a timeout. However it would most likely take a while with 30 000 records and refreshes, so you may wanna adjust your LIMIT ?, 1 to a higher number than 1 and go result() and foreach() multiple apis per pageload.