A batch query supports fetching data in batches, which can keep the memory usage under a limit.
This method will return a BatchQueryResult object which implements the [[\Iterator]] interface
and can be traversed to retrieve the data in batches.
For example,
php
$query = (new Query)->from('user');
foreach ($query->batch() as $rows) {
$rows is an array of 100 or fewer rows from user table
}
|
public batch ( integer $batchSize = 100, |
||
| $batchSize | integer | the number of records to be fetched in each batch. |
| $db | the database connection. If not set, the "db" application component will be used. | |
| return | the batch query result. It implements the [[\Iterator]] interface and can be traversed to retrieve the data in batches. | |
/**
* Perform a Database Query and show the result as CSV
*
* By default, write to the output buffer.
* But, if you set the filename, the file will be downloadable.
*
* @param string $filename Name of the file to download
*/
public function performAsCSV($filename = null)
{
// Create the CSV into memory
$csv = Writer::createFromFileObject(new SplTempFileObject());
// Insert fields names as the CSV header
$csv->insertOne($this->getCSVHeader());
// Print to the output stream
foreach ($this->query->batch() as $items) {
// $items is an array of 100 or fewer rows from the db table
$csv->insertAll($items);
}
$csv->output($filename);
}
public function testQuery()
{
$db = $this->getConnection();
// initialize property test
$query = new Query();
$query->from('customer')->orderBy('id');
$result = $query->batch(2, $db);
$this->assertTrue($result instanceof BatchQueryResult);
$this->assertEquals(2, $result->batchSize);
$this->assertTrue($result->query === $query);
// normal query
$query = new Query();
$query->from('customer')->orderBy('id');
$allRows = [];
$batch = $query->batch(2, $db);
foreach ($batch as $rows) {
$allRows = array_merge($allRows, $rows);
}
$this->assertEquals(3, count($allRows));
$this->assertEquals('user1', $allRows[0]['name']);
$this->assertEquals('user2', $allRows[1]['name']);
$this->assertEquals('user3', $allRows[2]['name']);
// rewind
$allRows = [];
foreach ($batch as $rows) {
$allRows = array_merge($allRows, $rows);
}
$this->assertEquals(3, count($allRows));
// reset
$batch->reset();
// empty query
$query = new Query();
$query->from('customer')->where(['id' => 100]);
$allRows = [];
$batch = $query->batch(2, $db);
foreach ($batch as $rows) {
$allRows = array_merge($allRows, $rows);
}
$this->assertEquals(0, count($allRows));
// query with index
$query = new Query();
$query->from('customer')->indexBy('name');
$allRows = [];
foreach ($query->batch(2, $db) as $rows) {
$allRows = array_merge($allRows, $rows);
}
$this->assertEquals(3, count($allRows));
$this->assertEquals('address1', $allRows['user1']['address']);
$this->assertEquals('address2', $allRows['user2']['address']);
$this->assertEquals('address3', $allRows['user3']['address']);
// each
$query = new Query();
$query->from('customer')->orderBy('id');
$allRows = [];
foreach ($query->each(100, $db) as $rows) {
$allRows[] = $rows;
}
$this->assertEquals(3, count($allRows));
$this->assertEquals('user1', $allRows[0]['name']);
$this->assertEquals('user2', $allRows[1]['name']);
$this->assertEquals('user3', $allRows[2]['name']);
// each with key
$query = new Query();
$query->from('customer')->orderBy('id')->indexBy('name');
$allRows = [];
foreach ($query->each(100, $db) as $key => $row) {
$allRows[$key] = $row;
}
$this->assertEquals(3, count($allRows));
$this->assertEquals('address1', $allRows['user1']['address']);
$this->assertEquals('address2', $allRows['user2']['address']);
$this->assertEquals('address3', $allRows['user3']['address']);
}
