How to control duplicated record in a form and entity?

Hi guys

I have a question

I have an entity and I want to insert a record in this entity i want to control and not allow to insert duplicated record

how should I do it?

of course I chose a solution for this as below

I have put an execute rule but it doesn't work the error is that the entity in the "var Entity = Me.getXPath("entity-list('POSRegistration','"+ Filter+"')");" is not known.

[1:42 AM, 9/4/2021] Anita.Totan: <POSRegistration.serialNumber>

var checkingSerialNumber = <POSRegistration.serialNumber> ;

if (activeFlag == 1 && <POSRegistration.serialNumber> != null)

{

var Filter ="checkingSerialNumber=" + <POSRegistration.serialNumber> ;

var Entity = Me.getXPath("entity-list('POSRegistration','"+ Filter+"')");

if (Entity.size() != 0)

{

<POSRegistration> = Entity[0].getXPath("Id");

<POSRegistration.isExistedtBefore>=true;

}

else

{

<POSRegistration>= null;

<POSRegistration.isExistedtBefore>=false;

}

}

this is my execute rule but in this line I have an error

var Entity = Me.getXPath("entity-list('POSRegistration','"+ Filter+"')");