将自定义字段添加到管理员（奏鸣曲）列表 Symfony 2.8

有一个表，其中显示来自 2 个表的数据，如何向该表添加另一个字段，该字段将根据其他 2 个表或一个表的条件包含信息，例如，我需要添加一个字段Trial，其中是基于字段的信息Price，如果字段Price大于 0，则Trial插入一个值，如果为 0，则插入另一个值。我以这种方式向方法中configureListFields添加了一个字段Trial：->add('trial')它已添加，现在如何用数据填充它，这是整个代码：

namespace AdminBundle\Admin;

use IntlDateFormatter;
use Sonata\AdminBundle\Admin\AbstractAdmin;
use Sonata\AdminBundle\Datagrid\DatagridMapper;
use Sonata\AdminBundle\Datagrid\ListMapper;
use Sonata\AdminBundle\Form\FormMapper;
use Sonata\AdminBundle\Route\RouteCollection;
use Sonata\AdminBundle\Show\ShowMapper;

class PurchaseAdmin extends AbstractAdmin
{
    protected $datagridValues = [
        '_page'       => 1,
        '_sort_order' => 'DESC',
        '_sort_by'    => 'createdAt',
    ];

    protected $accessMapping = [
        'refund' => 'REFUND',
    ];

    public function createQuery($context = 'list')
    {
        $query = parent::createQuery($context);

        $rootAlias = $query->getRootAliases()[0];
        $query->leftJoin($rootAlias.'.paymentTransaction', 'pt');
        $query->leftJoin($rootAlias.'.language', 'll');
        $query->addSelect('pt, ll');


        return $query;
    }

    public function configureRoutes(RouteCollection $collection)
    {
        parent::configureRoutes($collection);
        $collection->remove('delete');
        $collection->remove('create');
        $collection->remove('edit');
        $collection->add('refund', $this->getRouterIdParameter().'/refund');
        $collection->add('studentInfo', $this->getRouterIdParameter().'/student-info');
    }

    /**
     * @param DatagridMapper $datagridMapper
     */
    protected function configureDatagridFilters(DatagridMapper $datagridMapper)
    {
        $datagridMapper
            ->add(
                'teacher', null, [
                             'show_filter' => true
                         ]
            )
            ->add(
                'student', null, [
                             'show_filter' => true
                         ]
            )
            ->add(
                'language', null, [
                              'show_filter' => true
                          ]
            )
            ->add('lessonLength')
            ->add('lessons')
            ->add(
                'status', null, [], 'choice', [
                            'choices' => [
                                0 => 'created',
                                1 => 'paid',
                                2 => 'used',
                                3 => 'refunded',
                            ],
                        ]
            );
    }

    /**
     * @param ListMapper $listMapper
     */
    protected function configureListFields(ListMapper $listMapper)
    {
        $listMapper
            ->addIdentifier(
                'id',
                null,
                [
                    'route' => [
                        'name' => 'show'
                    ]
                ]
            )
            ->add('statusText')
            ->add('teacher')
            ->add('student')
            ->add(
                'studentInfo',
                'string',
                [
                    'template' => ':CRUD:list__action_student_info.html.twig'
                ]
            )
            ->add('language')
            ->add('lessonLength')
            ->add('lessons')
            ->add('lessonsLeft')
            ->add('price')
            ->add('trial')
            ->add('teacher.currency', null, ['label' => 'Currency'])
            ->add('paymentTransaction')
            ->add(
                'createdAt', 'datetime', [
                               'dateType' => IntlDateFormatter::SHORT,
                               'timeType' => IntlDateFormatter::SHORT,
                           ]
            )
            ->add(
                'updatedAt', 'datetime', [
                               'dateType' => IntlDateFormatter::SHORT,
                               'timeType' => IntlDateFormatter::SHORT,
                           ]
            )
            ->add(
                '_action',
                null,
                [
                    'actions' => [
                        'show'   => [],
                        'refund' => [
                            'template' => ':CRUD:list__action_refund.html.twig'
                        ],
                    ]
                ]
            );
    }

    /**
     * @param FormMapper $formMapper
     */
    protected function configureFormFields(FormMapper $formMapper)
    {
        $formMapper
            ->add('id')
            ->add('price')
            ->add('lessonLength')
            ->add('lessons')
            ->add('lessonsLeft')
            ->add('commission')
            ->add('status')
            ->add('createdAt')
            ->add('updatedAt');
    }

    /**
     * @param ShowMapper $showMapper
     */
    protected function configureShowFields(ShowMapper $showMapper)
    {
        $showMapper
            ->add('teacher')
            ->add('student')
            ->add('language')
            ->add('price')
            ->add('teacher.currency', null, ['label' => 'Currency'])
            ->add('lessonLength')
            ->add('lessons')
            ->add('lessonsLeft')
            ->add('commission')
            ->add('statusText')
            ->add('paymentTransaction')
            ->add('createdAt')
            ->add('updatedAt');
    }

    public function getTemplate($name)
    {
        if ($name === 'refund') {
            return ':Purchase:base_refund.html.twig';
        }

        return parent::getTemplate($name);
    }

}