<?xml version="1.0" encoding="UTF-8"?>
<doctrine-mongo-mapping xmlns="http://doctrine-project.org/schemas/odm/doctrine-mongo-mapping"
                        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                        xsi:schemaLocation="http://doctrine-project.org/schemas/odm/doctrine-mongo-mapping
                        http://doctrine-project.org/schemas/odm/doctrine-mongo-mapping.xsd">

    <mapped-superclass name="Vespolina\Entity\Order\BaseOrder">
        <field name="id"             id="true" strategy="INCREMENT"  />
        <field name="createdAt"      fieldName="createdAt"      type="date" />
        <field name="pricingSetData" fieldName="pricingSetData" type="hash" />
        <field name="state"          fieldName="state"          type="string" />
        <field name="totalPrice"     fieldName="totalPrice"     type="string" />
        <field name="updatedAt"      fieldName="updatedAt"      type="date" />
        <field name="attributes"     fieldName="attributes"     type="hash" strategy="set" />

        <reference-one field="owner"
                       fieldName="owner"
                       target-document="Vespolina\Entity\Partner\Partner"/>
        <embed-many field="items"
                    target-document="Vespolina\Entity\Order\Item"/>

    </mapped-superclass>
</doctrine-mongo-mapping>
<?xml version="1.0" encoding="UTF-8"?>
<doctrine-mongo-mapping xmlns="http://doctrine-project.org/schemas/odm/doctrine-mongo-mapping"
                        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                        xsi:schemaLocation="http://doctrine-project.org/schemas/odm/doctrine-mongo-mapping
                        http://doctrine-project.org/schemas/odm/doctrine-mongo-mapping.xsd">

    <mapped-superclass name="Vespolina\Entity\Order\BaseOrder">
        <field name="id"             id="true" strategy="INCREMENT"  />
        <field name="createdAt"      fieldName="createdAt"      type="date" />
        <field name="pricingSetData" fieldName="pricingSetData" type="hash" />
        <field name="state"          fieldName="state"          type="string" />
        <field name="totalPrice"     fieldName="totalPrice"     type="string" />
        <field name="updatedAt"      fieldName="updatedAt"      type="date" />
        <field name="attributes"     fieldName="attributes"     type="hash" strategy="set" />

        <reference-one field="owner"
                       fieldName="owner"
                       target-document="Vespolina\Entity\Partner\Partner">
            <cascade><all/></cascade>                                               
        </reference-one>
        <embed-many field="items"
                    target-document="Vespolina\Entity\Order\Item"/>

    </mapped-superclass>
</doctrine-mongo-mapping>

Add cascading to owner reference
Add cascading to owner reference