Using concat of data in an XPath expression returns an error

Question

Using concat of data in an XPath expression returns an error

Thomas Johnson 66

The syntax I’m using is a valid Xpath expression, but Logic Apps is returning an error. Using concat() inside of Xpath expression returns the following error: ... The template language function 'xpath' parameters are invalid: the 'xpath' parameter must ne a supported. well formed XPath expression. ...

I validated my XPath on several online XPath validators and tehy all retrun the correct result.

I'm using: '//trackingNumber/concat("https://mysite.com/",./text())'
and I expected to get an array of:
https://mysite.com/1233244
https://mysite.com/3443534
If I take out the concat and use: //trackingNumber/text() it works and I get:
1233244
3443534

Here is the json of the action:

"Initialize_variable": {  
   "inputs": {  
        "variables": [  
            {  
                "name": "Result",  
                "type": "array",  
                "value": "@xpath(xml('<root><trackingNumbers><trackingNumber>1233244</trackingNumber><trackingNumber>3443534</trackingNumber></trackingNumbers></root>'),'//trackingNumber/concat(\https://mysite.com/\,./text())')"  
            }  
        ]  
    },  
    "runAfter": {},  
    "type": "InitializeVariable"  
}

Does Logic App not support the concat()? If I just return the value using text() it works.

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Answer 1

MayankBargali-MSFT 70,936 Moderator

@Thomas Johnson You cannot use concat with xpath as first the concat will be evaluated and in case if there are any matching nodes or values then it will return the output (i.e. array values).

In the below example you can see I have used concat and concat will give the output as //trackingNumber/text() and then it will find the matching path in my variable xml.

   xpath(xml(variables('xml')),concat('//trackingNumber','/text()'))

The above will give the output as below:
1233244
3443534

If you change the expression as below the concat works correctly as it returns https://mysite.com//trackingNumber/text() but the xpath gives error as https://mysite.com//trackingNumber/text() is invalid xpath.

xpath(xml(variables('xml')),concat('https://mysite.com/','//trackingNumber/text()'))

Therefore it doesn't give you the expected output as you are looking for. The alternative will be evaluating the xpath first xpath(xml(variables('xml')),'//trackingNumber/text()') and once you have the array iterate it and append the https://mysite.com/ to a new array variable.

If you don't want to use multiple actions then you can offload this function to javascript inline code but this action needs an integration account on your logic app.

You can refer to Reference guide to expression functions for Azure Logic Apps for different methods and their usage. Hope the above clears things up.
Feel free to get back to me if you have any queries or concerns.

Thomas Johnson 66 Reputation points

2022-02-10T15:50:50.17+00:00
I'm not trying to use LogicApps' concat() to form the search parameter, but use XPath's concat() within the search parameter. Here is the actual search parameter it is failing on:

//trackingNumber/concat("https://mysite.com",./text())

concat() is a valid XPath function within XPath, like text(), but Logic Apps errors on it.

Here is a valid XPath Tester:xpath-tester.html

Use this for data:

<root><trackingNumbers><trackingNumber>1233244</trackingNumber><trackingNumber>3443534</trackingNumber></trackingNumbers></root>
MayankBargali-MSFT 70,936 Reputation points Moderator

2022-02-10T16:20:03.52+00:00

Thanks, @Thomas Johnson for your response. I do understand your concern that concat is not working as expected for you. But I will get the confirmation again from the team if this is supported. As per the document shared previously which talks about the different functions that logic app supports and we didn't see that concat supported with xpath in the examples too. Concat helps in the concating two or more strings and don't see it is valid for xpath as per your usage and logic app does return the error that the usage is incorrect.
MayankBargali-MSFT 70,936 Reputation points Moderator

2022-02-17T12:42:24.617+00:00

@Thomas Johnson I had a discussion with my product team and when we use different online parsers every parser behaves differently. The logic app uses .NET XPath and it does not appear to support such token as you were passing that is the reason it errors as not valid. As .NET XPath does not support it therefore logic app also doesn't support these types of tokens.

The workaround is the same as I have mentioned in my answer. Adding another workaround if you are using the Integration action you can always run a bit of XSLT. An XSLT to convert these kinds of scenarios is really straightforward.

Hope the above clears things up. Feel free to get back to me if you have any queries or concerns.
Thomas Johnson 66 Reputation points

2022-02-21T15:17:56.037+00:00
I wrote a C# app to test .NET XPath. And it doesn't support concat function, even though I see it was part of the XPath definition since 1.0.4.2.
concat
I ended up using Replace on the result, to achieve my goal.

replace(replace(replace(string(variables('TrackingNumbers')),'["','["$#%'),',"',',"$#%'),'$#%','https://mysite.com/')

Where variables('TrackingNumbers') is an array variable with eth results of the XPath.
MayankBargali-MSFT 70,936 Reputation points Moderator

2022-02-22T03:32:47.333+00:00

@Thomas Johnson The Mozilla reference document that you have shared is part of Javascript library. For dotnet it is part of System.XML namespace.

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Using concat of data in an XPath expression returns an error

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