Merge is creating not working for children @OneToMany

I am using Php Doctrine and I am using @OnToMany mapping with cascade all. I have a parent class SalesOrder and child class SalesOrderDetails.

1. 
   Case 1 : Save - When I save new record sales order along with sales order details. It is working as expected.


2. 
   Case 2 : Update - Here is the issue, I am merging the Sales Order which is fine however its inserting new records for its children SalesOrderDetail instead of updating it. Ideally it should it apply mergebut for children as well but its not.

As of now, I am getting the Sales Order Details by id from DB then change the properties of it. Ideally that should not be the case, mean if we set the id to unmanned object, it should update instead of creating new records.

Note:
1. Merge is working with parent object if it has the id value.
2. I am not adding new item here, I am just updating the existing recorded through merge.

SalesOrder.php

/**

 * @Entity @Table(name="sales_orders")

 * */

class SalesOrder extends BaseEntity {

       /**

       * @OneToMany(targetEntity="SalesOrderDetail",cascade="all", mappedBy="salesOrder" )

       */

       protected $itemSet;



           function __construct() {

                $this->itemSet = new ArrayCollection();

          }

}

SalesOrderDetail.php

/**

 * @Entity @Table(name="sales_order_details")

 * */

class SalesOrderDetail extends BaseEntity {



    /** @Id @Column(type="integer") @GeneratedValue * */

    protected $id;



    /**

     * @ManyToOne(targetEntity="SalesOrder")

     * @JoinColumn(name="order_no", referencedColumnName="order_no")

     */

    protected $salesOrder;



}

Debug Mode screen

If I use cascade={"merge"}

I am getting different error if I am using Cascades merge

Type: DoctrineORMORMInvalidArgumentException Message: Multiple
non-persisted new entities were found through the given association
graph: * A new entity was found through the relationship
'ZiletechDatabaseEntitySalesOrder#itemSet' that was not configured
to cascade persist operations for entity:
ZiletechDatabaseEntitySalesOrderDetail@0000000052218380000000007058b4a6.
To solve this issue: Either explicitly call EntityManager#persist() on
this unknown entity or configure cascade persist this association in
the mapping for example @ManyToOne(..,cascade={"persist"}). If you
cannot find out which entity causes the problem implement
'ZiletechDatabaseEntitySalesOrderDetail#__toString()' to get a
clue. * A new entity was found through the relationship
'ZiletechDatabaseEntitySalesOrder#itemSet' that was not configured
to cascade persist operations for entity:
ZiletechDatabaseEntitySalesOrderDetail@0000000052218071000000007058b4a6.
To solve this issue: Either explicitly call EntityManager#persist() on
this unknown entity or configure cascade persist this association in
the mapping for example @ManyToOne(..,cascade={"persist"}). If you
cannot find out which entity causes the problem implement
'ZiletechDatabaseEntitySalesOrderDetail#__toString()' to get a
clue.

You have a mistake in your mapping, cascade needs an array

/**

 * @OneToMany(targetEntity="SalesOrderDetail", cascade={"all"}, mappedBy="salesOrder" )

 */

 protected $itemSet;