Mule (Dataweave) transform JSON array to string - json

Question

This is probably simple, but everything I find in a search is only vaguely related to my question.
I have this:
{
"user":"C03999",
"caseNumber":"011-1234567",
"documents":[
{
"file":[
{"name":"indem1","document":"xSFSF%%GSF","mimeType":"PDF"},
{"name":"indem2","document":"xSFSF%%GSF","mimeType":"PDF"}
]
}
],
"mortgagee":"22995",
"billTo":"Originator",
"agreementDate":"2016-11-25",
"term":360,
"expirationDate":"2017-11-25",
"startDate":"Agreement",
"lenderEndorsed":true,
"lenderExecutedAgreement":false,
"indemnificationAgreementTransferable":false,
"qadLrsFileNumber":"2016-99999-9999",
"docketNumber":"2016-9999-99"
}
I would like to get this string out of it:
indem1,indem2
I created a global function:
<configuration doc:name="Configuration">
<expression-language autoResolveVariables="true">
<global-functions>
def convertToString(data){
return data.toString();
}
</global-functions>
</expression-language>
</configuration>
My transform looks like this:
%dw 1.0
%output application/csv
---
payload.documents.file map {
"" : convertToString($.name)
}
My output looks like:
[indem1\, indem2]
What do I need to do to get my desired string (indem1,indem2)?

Answer 1

Your question title says that " JSON array To string" but the dataweave code attached above has application/csv in the output.
Are you trying to convert into csv?? If that is the expectation, comma is a reserved character for .csv format and that is the reason , is getting escaped with backslash[indem1\,indem2].
If your intention is to convert into java, here is the code that returns String value.
%dw 1.0
%output application/java
payload.documents[0].file.*name joinBy ','

Answer 2

In general, if you have an object, and you need PART of that object to be written in a given format / MIME-type, use the write() function in the dw::Core module. If you need to read some content in an object that is JSON/JAVA/CSV and the rest is some other format, use the read() function in the same module.
For example, suppose you have payload as:
{
field1: "foo",
field2: { nested: "value" }
}
Further, suppose that you want the object to be JAVA, but the "field2" value to be seen as JSON. You can use this DW:
output application/java
---
{
field1: payload.field1,
field2: write(payload.field2,'application/json')
}
The result is:
{
field1: "foo",
field2: '{ "nested": "value" }'
}
NOTICE that "field2" now shows up as a nested JSON object, not a JAVA object. One way to tell is that the key in the JSON object is in quotes, but in a JAVA object they are not.