How to obtain all "Parents" associated with "Childs" provided that every "Child" instance has a given "myKey"?

<p dir="ltr" style="line-height: 1.15; margin-top: 0pt; margin-bottom: 0pt;"><span style="font-size: 15px; font-family: Arial; color: #3f4549; background-color: #ffffff; font-weight: bold; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">How to obtain all "Parents" associated with &nbsp;"Childs" provided that every "Child" instance has a given "myKey"?</span></p> <p dir="ltr" style="line-height: 1.15; margin-top: 0pt; margin-bottom: 0pt;">&nbsp;</p> <p dir="ltr" style="line-height: 1.15; margin-top: 0pt; margin-bottom: 0pt;">In order to give all Children for particular Parent use the following:</p> <p dir="ltr" style="line-height: 1.15; margin-top: 0pt; margin-bottom: 0pt;"><br />https://api.quickblox.com/data/Child?_parent_id=<your_Parent_class_instance_id></p> <p dir="ltr" style="line-height: 1.15; margin-top: 0pt; margin-bottom: 0pt;">&nbsp;</p> <p dir="ltr" style="line-height: 1.15; margin-top: 0pt; margin-bottom: 0pt;">To give all 'Parents' ids associated with&nbsp; "Childs" where every "Child" instance has a given "myKey" use:<br />https://api.quickblox.com/data/Child?myKey=&lt;some_value></p> <p dir="ltr" style="line-height: 1.15; margin-top: 0pt; margin-bottom: 0pt;">&nbsp;</p> <p dir="ltr" style="line-height: 1.15; margin-top: 0pt; margin-bottom: 0pt;">As a result each Child has _parent_id field.</p> <p>&nbsp;</p>