How write formula on Polish TIN (taxpayer identification number) using that like Validation rule

Question

Who knows how best to approach this task. I was asked to add a TIN field to Account. This is the Polish taxpayer number for the firm. This field should be checked to be sure that the user entered it correctly. At the bottom under the text I leave a screenshot according to which rule this number is checked. Is it possible to do something like this using Validation rule and the formulas it contains?

I've achieved something. I wrote a formula that would check the TIN. In my opinion, it should look like below in the insert with the code.

MOD(
(VALUE((MID( NIP__c , 0, 1)) * 6) +
(VALUE((MID( NIP__c , 1, 1)) * 5) + 
(VALUE((MID( NIP__c , 2, 1)) * 7) + 
(VALUE((MID( NIP__c , 3, 1)) * 2) + 
(VALUE((MID( NIP__c , 4, 1)) * 3) + 
(VALUE((MID( NIP__c , 5, 1)) * 4) + 
(VALUE((MID( NIP__c , 6, 1)) * 5) + 
(VALUE((MID( NIP__c , 7, 1)) * 6) + 
(VALUE((MID( NIP__c , 8, 1)) * 7),
11)  > 10

But for some reason a record returns to me with an error of the following content: Error: Syntax error. Missing ')'

I would be very grateful if someone would rate my formula and tell me if it is well written in general and where I need to put the parentheses. Because I have already run out of all possible options for how to put them.

Thank you for checking the original formula and for the explanations related to the placement of brackets. I've moved on. But my ValidationRule does not work as it should. This is what my formula looks like now.

MOD(
VALUE((MID( NIP__c , 0, 1))) * 6 +
VALUE((MID( NIP__c , 1, 1))) * 5 + 
VALUE((MID( NIP__c , 2, 1))) * 7 + 
VALUE((MID( NIP__c , 3, 1))) * 2 + 
VALUE((MID( NIP__c , 4, 1))) * 3 + 
VALUE((MID( NIP__c , 5, 1))) * 4 + 
VALUE((MID( NIP__c , 6, 1))) * 5 + 
VALUE((MID( NIP__c , 7, 1))) * 6 + 
VALUE((MID( NIP__c , 8, 1))) * 7,
11)     =    10
 && 
MOD(
VALUE((MID( NIP__c , 0, 1))) * 6 +
VALUE((MID( NIP__c , 1, 1))) * 5 + 
VALUE((MID( NIP__c , 2, 1))) * 7 + 
VALUE((MID( NIP__c , 3, 1))) * 2 + 
VALUE((MID( NIP__c , 4, 1))) * 3 + 
VALUE((MID( NIP__c , 5, 1))) * 4 + 
VALUE((MID( NIP__c , 6, 1))) * 5 + 
VALUE((MID( NIP__c , 7, 1))) * 6 + 
VALUE((MID( NIP__c , 8, 1))) * 7,
11)      <>      VALUE(MID( NIP__c , 9, 1))

It should check whether the entered TIN is correct. The first task The next task. This is so that the second part of the formula checks that the last digit with TIN is equal to MOD 11. As in the screenshot below.

But in my case it looks like I can enter all the numbers and ValidationRule will accept everything. Unless it's just 9999999999

Who could help me at this stage of the Validation Rule build? Because at this stage everything has somehow changed places. ValidationRule accepts everything, there are no syntactic or any other errors, but I'm still not happy with the result. I've reached a dead end and now I don't know what to do with it all.

Answer 1

You should look at your formula and try to spot where you might have an error by minimizing it:

MOD(
(VALUE((MID( NIP__c , 0, 1)) * 6) +
(VALUE((MID( NIP__c , 1, 1)) * 5) + 
(VALUE((MID( NIP__c , 2, 1)) * 7) + 
(VALUE((MID( NIP__c , 3, 1)) * 2) + 
(VALUE((MID( NIP__c , 4, 1)) * 3) + 
(VALUE((MID( NIP__c , 5, 1)) * 4) + 
(VALUE((MID( NIP__c , 6, 1)) * 5) + 
(VALUE((MID( NIP__c , 7, 1)) * 6) + 
(VALUE((MID( NIP__c , 8, 1)) * 7),
11)  > 10

Here we can see that first and last lines are just the parenthesis/brackets for the MOD function, so if you ignore whatever is in the middle, you will get:

MOD(X, 11) >10

Which looks good. Then the error is not there. Let's look inside the first element of your MOD function:

all lines are generally the same, so let's review only 1 of them in more detail:

(VALUE((MID( NIP__c , 0, 1)) * 6)

Here we have this in the middle:

MID( NIP__c , 0, 1)

Which is good, so let's call it X for now. Then we have:

(VALUE((X) * 6)

We can remove the brackets from around X, so the result is:

(VALUE(X * 6)

So you see that we have an unclosed opening bracket. The solution would be to remove that opening bracket on each line

Answer 2

In its current state, I think the only thing you need to get your validation rule working is to change the && (the "AND" operator) to || (the "OR" operator).

Validation rules prevent records from being saved when the overall result is true. This is kinda non-intuitive (at least for me, a programmer), and I find it helps to think of them as actually being invalidation rules. The goal here is to describe when your data is invalid.

If you aren't familiar with Boolean logic,
AND returns true only when all of the things being "and"ed together are true. (e.g. true && true && true == true)
OR returns true if any of the things being "or"d together are true. (e.g. false || false || true == true)

When you're using AND, you're saying that both the mod(<sum>, 11) needs to be 10 and the check digit needs to not match. In reality, either of those conditions being true mean that the TIN is invalid.

Another fundamental bit of Boolean logic is DeMorgan's Law. Applying a ! (the "NOT" operator, which flips true and false, so !false == true and !true == false) to something containing "AND" and/or "OR" also flips the "AND"/"OR" operators.

All of that is to say that if A is "mod(sum, 11) != 10", and B is "mod(sum, 11) == check digit", then
!(A && B) and
!A || !B
are equivalent

So you're looking for "mod(sum, 11) == 10 OR mod(sum, 11) != check digit"

MOD(
    VALUE(MID( NIP__c , 0, 1)) * 6 +
    VALUE(MID( NIP__c , 1, 1)) * 5 + 
    VALUE(MID( NIP__c , 2, 1)) * 7 + 
    VALUE(MID( NIP__c , 3, 1)) * 2 + 
    VALUE(MID( NIP__c , 4, 1)) * 3 + 
    VALUE(MID( NIP__c , 5, 1)) * 4 + 
    VALUE(MID( NIP__c , 6, 1)) * 5 + 
    VALUE(MID( NIP__c , 7, 1)) * 6 + 
    VALUE(MID( NIP__c , 8, 1)) * 7,
    11
) = 10
|| 
MOD(
    VALUE(MID( NIP__c , 0, 1)) * 6 +
    VALUE(MID( NIP__c , 1, 1)) * 5 + 
    VALUE(MID( NIP__c , 2, 1)) * 7 + 
    VALUE(MID( NIP__c , 3, 1)) * 2 + 
    VALUE(MID( NIP__c , 4, 1)) * 3 + 
    VALUE(MID( NIP__c , 5, 1)) * 4 + 
    VALUE(MID( NIP__c , 6, 1)) * 5 + 
    VALUE(MID( NIP__c , 7, 1)) * 6 + 
    VALUE(MID( NIP__c , 8, 1)) * 7,
    11
) <> VALUE(MID( NIP__c , 9, 1))

+bonus:
for a little bit of fun, since I mentioned it would be easier to do this in code, here's what the code could look like

public Boolean validateTIN(String tin){
    List<Integer> multipliers = new List<Integer>{6, 5, 7, 2, 3, 4, 5, 6, 7};
    Integer checkDigit = Integer.valueOf(tin.right(1));
    Integer mod11Sum = 0;

    for(Integer i = 0; i < 9; i++){
        mod11Sum += Integer.valueOf(tin.mid(i, 1)) * multipliers[i];
    }

    mod11Sum = Math.mod(mod11Sum, 11);
    return (mod11Sum != 10 && mod11Sum == checkDigit);
    // The inverse would also work
    //return !(mod11Sum == 10 || mod11Sum != checkDigit);
}