laravel cursor的底层实现

foreach (BillInfo::where('id', '>', 0)->orderBy('id', 'desc')->limit(10000)->cursor() as $value) {    print_r($value);}

Illuminate\Database\Query\Builder.php;

/** * Get a generator for the given query. * * @return \Generator */public function cursor(){    if (is_null($this->columns)) {        $this->columns = ['*'];    }    return $this->connection->cursor(        $this->toSql(), $this->getBindings(), ! $this->useWritePdo    );}

Illuminate\Database\Connection.php;

/** * Run a select statement against the database and returns a generator. * * @param  string  $query * @param  array  $bindings * @param  bool  $useReadPdo * @return \Generator */public function cursor($query, $bindings = [], $useReadPdo = true){    $statement = $this->run($query, $bindings, function ($query, $bindings) use ($useReadPdo) {        if ($this->pretending()) {            return [];        }        // First we will create a statement for the query. Then, we will set the fetch        // mode and prepare the bindings for the query. Once that's done we will be        // ready to execute the query against the database and return the cursor.        $statement = $this->prepared($this->getPdoForSelect($useReadPdo)                          ->prepare($query));        $this->bindValues(            $statement, $this->prepareBindings($bindings)        );        // Next, we'll execute the query against the database and return the statement        // so we can return the cursor. The cursor will use a PHP generator to give        // back one row at a time without using a bunch of memory to render them.        $statement->execute();        return $statement;    });    while ($record = $statement->fetch()) {        yield $record;    }}