Call querry in operation



I've a text field in my form where I enter a number, then I created a local variable with the datatype "Long" and my first operation converts the value from my textfields into long (the textfields allow only numbers as Input).
Now I want to get a Business data model objekt in my next Operation. For that I tried to use the querry "findByPersistenceId" and I entered my Long as the variable. But as soon as aI click on ok the Operation only displays the querry without the Parameter and when I click on edit again the "value" field is empty again.
Is this normal? Because something isn't working and I can't get a entry from my bdm.

Thanks for any help!

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