为什么此PHP代码对数组进行排序未返回正确的值？

Question

I have an array of products that I'm pulling from the db. I've verified that these are correct, using the following code:

$unsorted_products = products::get( array( 'collection' => $collection->id ) );
die(print_r($unsorted_products));

...and the results are as I expect. The thing is, I need the results to basically be grouped by a parent category and category. How they're sorted within each grouping, I don't care. Given that I don't have access to change the model that is retrieving the data via SQL, I need to sort this array via PHP. I'm using the following code:

$products = usort($unsorted_products, function ($a, $b) {
        return strcmp(
            $a->parentcategory.$a->categoryname,
            $b->parentcategory.$b->categoryname
        );
    });

...but dumping the $products array reveals that it is only holding the value 1. Any idea what I am doing wrong? I've verified that the properties I am attempting to access do exist in each object.

Thanks.

Answer 1

It sorts the input array.

From the usort manual:

Returns TRUE on success or FALSE on failure.

Answer 2

You are doing it wrong. usort doesn't return array, it returns ether true or false. It changes array that you pass as first parameter.

After your code is executed, $unsorted_products becomes sorted array. Do this:

$products = products::get( array( 'collection' => $collection->id ) );

and this:

usort($products, function ($a, $b) {
        return strcmp(
            $a->parentcategory.$a->categoryname,
            $b->parentcategory.$b->categoryname
        );
    });