php数组警告：非法字符串偏移量

Question

我遇到了将数组的值放入表格

的问题

这是查询

public function getAllAulasSemDespacho(){
    try {
        $stmt = $this->db->prepare("SELECT a.Atividade, a.Local, a.DataAula, ae.idAula, p.Nome, t.Turma
                                    FROM
                                        aulaexteriorturmas AS ae
                                        INNER JOIN turmas AS t
                                        ON (ae.idTurma = t.idTurma)
                                        INNER JOIN aulaexterior  AS a 
                                        ON (ae.idAula = a.idAula)
                                        INNER JOIN professores AS p
                                        ON (a.idProfessor = p.idProfessor) WHERE a.Autorizado IS NULL ");
        if (!$stmt->execute()) {
            print_r($stmt->errorInfo());
            return false;
        } else {
            $result = $stmt->fetchAll(PDO::FETCH_ASSOC);
            $aulas_array = array();
            foreach ($result as $row) {
                $idAula = $row['idAula'];
                if (!isset($aulas_array[$idAula])) {
                    $aulas_array[$idAula]['idAula'] = $row['idAula'];
                    $aulas_array[$idAula]['Atividade'] = $row['Atividade'];
                    $aulas_array[$idAula]['Local'] = $row['Local'];
                    $aulas_array[$idAula]['DataAula'] = $row['DataAula'];
                    $aulas_array[$idAula]['Nome'] = $row['Nome'];
                    $aulas_array[$idAula]['equip'] = array();
                }
                $aulas_array[$idAula]['Turma'][] = $row['Turma'];
            }
            foreach ($aulas_array as $idAula => $aulas) {
                return $aulas;
            }

        }
    } catch (PDOException $e) {
        echo $e->getMessage();
    }
}

从我的主页中我有var_dump

 array(7) { ["idAula"]=> string(1) "5" ["Atividade"]=> string(33) "Rui Vitória convoca 28 jogadores" ["Local"]=> string(7) "Algarve" ["DataAula"]=> string(10) "2017-08-31" ["Nome"]=> string(22) "XXXXXXXXX" ["equip"]=> array(0) { } ["Turma"]=> array(2) { [0]=> string(4) "5ºC" [1]=> string(4) "6ºB" } } 

我想在此表中收到这些值

<?php
    if (!empty($aulasListagem)) {
        foreach ($aulasListagem as $row) {
            print_r($row);
            ?>
            <tr>
                <td align="center"><?php echo $row['Atividade']; ?></td>
                <td align="center"><?php echo $row['Local']; ?></td>
                <td align="center"><?php echo $row['DataAula']; ?></td>
                <td align="center"><?php echo $row['Nome']; ?></td>
                <td align="center"><?php echo $row['Turma']; ?></td>
                <td><a data-toggle="modal" data-id="<?php echo $row['idAula']; ?>"
                       class="open-AddDialog btn btn-sm btn-success center-block"
                       href="#myModalDespachoAula">Opção</a></td>
            </tr>
            <?php
        }
    }
?>

从我的查询中看起来一切都还可以，但是当我想要全部进入我的表时会收到警告：所有字段的非法字符串偏移'DataAula'

我做错了什么？

由于