Laravel中chunk方法分块处理数据

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我只说从今往后，不说今日以前。
Let’s imagine the situation: you have a big database table (like 10 000 rows or bigger) and you need to run an update to one column. But you cannot run just SQL query – there is some PHP logic behind it. So foreach loop could potentially take forever or bump into a default 30-second script limit. Luckily, Laravel has a neat solution for it.

Let’s look at a simple example of a problem I’m talking about:

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$users = User::all();
foreach ($users as $user) {
  $some_value = ($user->some_field > 0) ? 1 : 0;
  // might be more logic here
  $user->update(['some_other_field' => $some_value]);
}

Do you see the problem? It’s fine for a DB table with 100 or 500 users. But what about 10000? 100000? Million?
It’s not only about the speed, but also about storing the data – you are potentially storing the whole database table into variables, you might run out of memory.

So here’s the thing: there is a function called chunk() which splits all data into separate selects, like pagination.
Let’s look at an example:

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User::chunk(100, function ($users) {
  foreach ($users as $user) {
    $some_value = ($user->some_field > 0) ? 1 : 0;
    // might be more logic here
    $user->update(['some_other_field' => $some_value]);
  }
});

http://www.jianshu.com/p/5dafd0d6e69a