CODEWITHSUNDEEP
xsltconditional-statements
user2191439
user2191439

Reputation: 261

Weird behavior of the != XPath operator

I'm attempting to create an xsl:choose statement with multiple conditions to test. So far, I have this:

<xsl:choose>
    <xsl:when test="$AccountNumber != '12345' and $Balance != '0'">
       <do stuff here>
       ...

The problem is that the 'and' is being treated as an 'or'. If the account number is 12345 or the balance of an account is 0, the condition is treated as true and the code gets executed. I need the test to be that both conditions must be true... do I have the syntax wrong here?

Thanks in advance, ~Tim

Upvotes: 26

Views: 115561

Answers (3)

JLRishe
JLRishe

Reputation: 101652

If $AccountNumber or $Balance is a node-set, then this behavior could easily happen. It's not because and is being treated as or.

For example, if $AccountNumber referred to nodes with the values 12345 and 66 and $Balance referred to nodes with the values 55 and 0, then $AccountNumber != '12345' would be true (because 66 is not equal to 12345) and $Balance != '0' would be true (because 55 is not equal to 0).

I'd suggest trying this instead:

<xsl:when test="not($AccountNumber = '12345' or $Balance = '0')">

$AccountNumber = '12345' or $Balance = '0' will be true any time there is an $AccountNumber with the value 12345 or there is a $Balance with the value 0, and if you apply not() to that, you will get a false result.

Upvotes: 8

Dimitre Novatchev
Dimitre Novatchev

Reputation: 243459

The problem is that the 'and' is being treated as an 'or'.

No, the problem is that you are using the XPath != operator and you aren't aware of its "weird" semantics.

Solution:

Just replace the any x != y expressions with a not(x = y) expression.

In your specific case:

Replace:

<xsl:when test="$AccountNumber != '12345' and $Balance != '0'">

with:

<xsl:when test="not($AccountNumber = '12345') and not($Balance = '0')">

Explanation:

By definition whenever one of the operands of the != operator is a nodeset, then the result of evaluating this operator is true if there is a node in the node-set, whose value isn't equal to the other operand.

So:

 $someNodeSet != $someValue

generally doesn't produce the same result as:

 not($someNodeSet = $someValue)

The latter (by definition) is true exactly when there isn't a node in $someNodeSet whose string value is equal to $someValue.

Lesson to learn:

Never use the != operator, unless you are absolutely sure you know what you are doing.

Upvotes: 44

Severin Foreman
Severin Foreman

Reputation: 123

I've always used this syntax, which yields more predictable results than using !=.

<xsl:when test="not($AccountNumber = '12345') and not($Balance = '0')" />

Upvotes: 0

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