Convert Number to String in XSLT in WSO2

I have an xml payload that looks like this:

<Product>
<ProductId>790982</ReceiptId>
<Qty>78</Qty>
<Product>
<Product>
<ProductId>WS-5678</ReceiptId>
<Qty>34</Qty>
<Product>

I need to transform using xslt and send it to another system. I am using xsl:value-of to extract the values, but after conversion the first ProductId comes out as a number and the second ProductId comes out as a String.

 <itemRef> <xsl:value-of select="/ProductId"/>   </itemRef>

I want to convert every ProductId to a string. I've seen a fix where we need to add conf in synapse-properties file. But that would convert every Number to String. Is there any way I can do it only for ProductId by checking if its a number or a string? I've tried concat function as below to add double quotes across the number but that doesn't work.

 <xsl:variable name="quot">"</xsl:variable>
 <xsl:variable name="sku" select="/ProductId"/>
<itemRef>   <xsl:value-of select="concat($quot, $sku,$quot)"/>  </itemRef>

You can use a custom JSON Schema along with JSON Transform Mediator for this.

Assuming you want to do the following conversion.

<products>
    <Product>
        <ProductId>790982</ProductId>
        <Qty>78</Qty>
    </Product>
    <Product>
        <ProductId>WS-5678</ProductId>
        <Qty>34</Qty>
    </Product>
</products>

To

{
    "products": {
        "Product": [
            {
                "ProductId": "790982",
                "Qty": 78
            },
            {
                "ProductId": "WS-5678",
                "Qty": 34
            }
        ]
    }
}

First Create a Local Entry with the JSON Schema like below.

<?xml version="1.0" encoding="UTF-8"?>
<localEntry key="JsonSchema" xmlns="http://ws.apache.org/ns/synapse"><![CDATA[
{
	"$schema": "http://json-schema.org/draft-07/schema#", 
	"type": "object",
	"required": [
		"products"
	],
	"properties": {
		"products": {
			"type": "object",
			"required": [
				"Product"
			],
			"properties": {
				"Product": {
					"type": "array",
					"items":{
						"type": "object",
						"properties": {
							"ProductId": {
								"type": "string"
							},
							"Qty": {
								"type": "integer"
							}
						}
					}
				}
			}
		}
	}
}
]]></localEntry>

Then after the XSLT mediator add the following pointing to the above schema.

<property name="messageType" scope="axis2" type="STRING" value="application/json"/>
<jsontransform schema="JsonSchema"/>