想要用json字段内的键来作为关联的外键，有可行办法么？

class Category extends Model
{
    protected $casts = [
        'ext'    => 'json',
    ];
}
# 不可用
Category::resolveRelationUsing('supplier', function (Category $category) {
    return $category->belongsTo(Supplier::class, 'ext.supplier_id');
});

# 不可用
Category::resolveRelationUsing('supplier', function (Category $category) {
    return $category->belongsTo(Supplier::class,  'ext->supplier_id');
});Copy