我有以下两个实体：

/** @Entity @Table(name="invoice") */
class Invoice {
    /** @Id @Column(type="integer") @GeneratedValue */
    protected $id;
    ...
    /** @OneToMany(targetEntity="InvoiceRow", mappedBy="invoice", fetch="EAGER", cascade={"persist", "remove"}, orphanRemoval=true) */
    protected $rows = null;
    ...

    public function __construct() {
        $this->rows = new ArrayCollection();
    }
    ...

    public function getRows() {
        return $this->rows;
    }

    public function addRow($row) {
        $this->rows[] = $row;
        $row->setInvoice($this);
    }

    public function emptyRows() {
        $this->rows = new ArrayCollection();
    }
}

/** @Entity @Table(name="invoice_row") */
class InvoiceRow {
    /** @Id @Column(type="integer") @GeneratedValue */
    protected $id;
    ...
    /** @ManyToOne(targetEntity="Invoice", inversedBy="rows") */
    protected $invoice;
    ...
    
    public function getInvoice() {
        return $this->invoice;
    }

    public function setInvoice($invoice) {
        $this->invoice = $invoice;
    }
}

因此，一个Invoice的示例可以关联许多InvoiceRow的示例。在DB上反映实体结构之后，我在表invoice_row中有字段invoice_id，它正确地引用了表invoice的相关记录的id。
由于可以添加、删除或修改发票的每一行，因此每次保存发票时，我都希望删除InvoiceRow的所有关联记录，并在从前端接收到这些记录时重新创建这些记录。
这是代码：

public static function saveInvoice($invoiceData, $invoiceRows) {
    $em = getEntityManager();

    $dbInvoice = null;
    if ($invoiceData->id) {
        // if is an exsisting invoice, i get it from the DB, so Doctrine will execute an update instead of an insert
        $dbInvoice = $em->find(Invoice::class, $invoiceData->id);
    }

    $dbInvoice->emptyRows(); // deleting all the rows from the entity Invoice

    // adding all the rows, as they were received from the frontend
    foreach ($invoiceRows as $invoiceRow) {
        $dbInvoiceRow = self::getDbInvoiceRow($invoiceRow) // map frontend object into the Doctrine entity InvoiceRow
        $dbInvoice->addRiga($dbInvoiceRow);
    }

    $em->persist($dbInvoice);
    $em->flush();
}

问题是，最后，不是只有从前端接收的行，而是仍然有所有旧的行，因为没有删除任何行。
举例来说：invoice_row表中的原始数据：

| id | invoice_id | code | description |
| -- | ---------- | ---- | ----------- |
| 1  | 12         | 010  | product 01  |
| 2  | 12         | 008  | product 02  |

从前端接收的行：

| code | description |
| ---- | ----------- |
| 010  | product 01  |
| 012  | product 03  |

invoice_row表的预期内容：

| id | invoice_id | code | description |
| -- | ---------- | ---- | ----------- |
| 1  | 12         | 010  | product 01  |
| 3  | 12         | 012  | product 03  |

坚持后的真实的内容

| id | invoice_id | code | description |
| -- | ---------- | ---- | ----------- |
| 1  | 12         | 010  | product 01  | -> old row
| 2  | 12         | 008  | product 02  | -> old row
| 3  | 12         | 010  | product 01  |
| 4  | 12         | 012  | product 03  |

我做错了什么？
提前感谢大家。