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Using Buffer for Resultset::rewind() after Resultset::next() called in Zend\Db

Posted in hack, Tutorial PHP, Zend Framework 3 by samsonasik on August 5, 2019

In Zend\Db, there is Resultset which can be used as result of db records as instanceof PHP Iterator. For example, we have the following table structure:

CREATE TABLE test (
    id serial NOT NULL PRIMARY KEY,
    name character varying(255)
);

and we have the following data:

To build resultset, we can use the following code:

include './vendor/autoload.php';

use Zend\Db\Adapter\Adapter;
use Zend\Db\TableGateway\TableGateway;
use Zend\Db\ResultSet\ResultSet;

$adapter = new Adapter([
    'username' => 'developer',
    'password' => '123456',
    'driver'   => 'pdo_pgsql',
    'database' => 'learn',
    'host'     => 'localhost',
]);

$resultSetPrototype = new ResultSet(
    null,
    new ArrayObject([], ArrayObject::ARRAY_AS_PROPS)
);

$tableGateway = new TableGateway(
    'test',
    $adapter,
    null,
    $resultSetPrototype
);

$select    = $tableGateway->getSql()->select();
$resultSet = $tableGateway->selectWith($select);

On getting the data, we can go to specific record position by using next(), for example: we want to get the 2nd record of selected data, we can use the following code:

$resultSet->current();
$resultSet->next();

var_dump($resultSet->current());

and we will get the following data:

class ArrayObject#16 (1) {
  private $storage =>
  array(2) {
    'id' =>
    int(2)
    'name' =>
    string(6) "test 2"
  }
}

However, when we need to back to first position, we can’t just use rewind() as follow:

$resultSet->rewind();
var_dump($resultSet->current());

Above code will result wrong data, which is a next record data:

class ArrayObject#16 (1) {
  private $storage =>
  array(2) {
    'id' =>
    int(3)
    'name' =>
    string(6) "test 3"
  }
}

To make that work, we need to use buffer() method early after result set created, so, the code will need to be:

$select    = $tableGateway->getSql()->select();
$resultSet = $tableGateway->selectWith($select);

$resultSet->buffer();

$resultSet->current();  // ensure hit 1st record first 
$resultSet->next();     // next position

var_dump($resultSet->current()); // get 2nd record 

$resultSet->rewind(); // back to position 0
var_dump($resultSet->current());  // get 1st record again 

That will show the correct data:

# second record by call of next()
class ArrayObject#16 (1) {
  private $storage =>
  array(2) {
    'id' =>
    int(2)
    'name' =>
    string(6) "test 2"
  }
}

# first record after call of rewind() 
class ArrayObject#16 (1) {
  private $storage =>
  array(2) {
    'id' =>
    int(1)
    'name' =>
    string(6) "test 1"
  }
}

3 Responses

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  1. bkilinc said, on August 5, 2019 at 8:13 pm

    on $records->buffer();
    where does records come from? or should it be $resultSet?
    and why do we prefer
    $select = $tableGateway->getSql()->select();
    $resultSet = $tableGateway->selectWith($select);
    instead of
    $resultSet = $tableGateway->select();

    • samsonasik said, on August 6, 2019 at 8:25 am

      Thank you, that’s should be `$resultSet`, it fixed now. Getting `$select` from `getSql()` first make it possible to do other thing before return a resultset with ease, eg: sorting, for example:

      $select = $tableGateway->getSql()->select();
      $select->order('id ASC');
      $resultSet = $tableGateway->selectWith($select);
      
      • bkilinc said, on August 6, 2019 at 2:30 pm

        thanks. I mostly do something like this.
        $resultSet = $tableGateway->select(function($select) { $select->order(‘id ASC’); });
        Just asked out of curiosity. As I did not use selectWith much.


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