What you can do is try one of the following things:
1 Check with an isNew function
Use the isNew function within the decision to check if your object has been created before. This is handy to quickly check if you are editing or creating. If you want to see if you already have an object in the databased with similar attributes, use number 2
2 Check with an Xpath retrieve
If you perform an Xpath retrieve, you can define attributes using the form of:
[object/attribute = attribute]
check the following documentation: https://docs.mendix.com/refguide/xpath
by doing so you can create a retrieve that finds all objects that are similar. If any are found you can determine that you have already created the object.