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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