laravelcursor的底层实现

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

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Illuminate\Database\Query\Builder.php;

/**
 * Get a generator for the given query.
 *
 *@return\Generator
 */
public functioncursor()
{
    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  $useReadPdo
 *@return\Generator
 */
public functioncursor($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;
    }
}

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