The Converter Lab · Nest Labs

Before you start

What a converter step actually does

A converter changes the format of the payload without changing what it says. The same order, expressed as CSV instead of XML. No mapping, no script — you drop the step in, point it at the shape of your data, and the body comes out the other side in a different notation.

Open the Converter palette and you will find six of them. Look at the names and something jumps out: every single one has XML on one side.

CSV to XML and XML to CSV — flat files in and out.
JSON to XML and XML to JSON — REST APIs in and out.
EDI to XML and XML to EDI — B2B, and out of scope here.

There is no CSV-to-JSON converter, and there never will be. If you searched for one, that is the answer: XML is the hub, and anything-to-anything means two steps through it. CSV in, XML in the middle, JSON out. That is not a limitation to work around — it is the design, and once you see it the palette stops looking arbitrary.

The other thing worth knowing before you start: converting JSON is not symmetrical. One record becomes an object, several become an array, and the same converter produces a different shape depending on how many rows happened to arrive that day. That is the trap this lab walks you into on purpose in Task 2, because it is far better to meet it here than in production on a quiet Tuesday when only one order came through.

In this lab you will chain four converters in both directions, then deliberately break three payloads and name the error from the symptom alone — which is the skill that actually saves you time later.

What you will learn

XML is the hub — always

Chain CSV → XML → JSON, because no single step does CSV-to-JSON.
Meet the array trap: one record produces an object, many produce an array.
Turn JSON back to XML, and flatten XML into a CSV report.
Read a converter error and name the cause from the symptom alone.

Look at the six entries in the Converter palette and one thing jumps out: every single one has XML on one side. There is no CSV-to-JSON converter, and there never will be — everything routes through XML.

The palette, and what this lab covers
Converter step	Direction	In this lab
CSV to XML	flat file → hub	Task 1
XML to JSON	hub → REST	Task 2
JSON to XML	REST → hub	Task 3
XML to CSV	hub → flat file	Task 4
EDI ↔ XML	B2B	Out of scope

Before you start

What you need

Prerequisites
Item	Why
Lab 01 — Content Modifier	You reuse the sender-with-no-receiver trick and Content Modifier headers.
CPI trial tenant + `ESBMessaging.send`	To create three flows and deploy them.
Postman	Send raw `text/csv`, `application/json`, `application/xml` and read the response.

Set up three tiny flows

15 minNot graded

Create a package Training_Converters_XX and three flows: Conv_A_CSV_to_JSON, Conv_B_JSON_to_XML, Conv_C_XML_to_CSV.
Give each an HTTPS sender (addresses /conv-a-XX, /conv-b-XX, /conv-c-XX), ESBMessaging.send, no receiver, Log Level Trace.
Deploy all three and confirm each echoes back what you POST.

Before you add a single converterAll three endpoints must return HTTP 200 with your input echoed. Debugging a converter on top of a broken endpoint is the slow way.

Turn a headerless CSV into XML

CSV to XML35 min25 marks

The CSV converter cannot guess a structure — you hand it one. Writing that little XSD is the whole lesson.

CSV to XML Converter · configuration
Field	Value
XML Schema	Orders.xsd (add it to the flow resources)
Path to Target Element	/Orders/Order
Field Separator	,

VerifyThree <Order> elements, six children each, values in the right elements. If a SKU lands inside <CustomerId>, your XSD element order does not match the column order.

Why is Quantity a string, not a number? · 5 marks. A CSV file carries no type information at all.

Chain a second converter and meet the array trap

XML to JSON25 min20 marks

Two converters back to back give CSV→JSON, which no single step can do. Then you meet the behaviour that breaks more REST integrations than any other.

The point of the taskPOST three rows → JSON Order is an array. POST one row → it is an object. With a single occurrence the XML looks like a non-repeating element, so the converter emits no array — and an API expecting [ ] rejects it.

Write it up · 8 marks. Paste both responses, say why the shape changed, and name one way to force an array every time.

JSON into the hub format

JSON to XML20 min20 marks

This converter needs no schema — JSON already describes its structure. It has one hard rule, and you hit it on purpose.

VerifyA payload with one root member converts. A payload with two root members fails — an XML document can only have one root, and the converter cannot invent a parent for two siblings.

Deliverable · 8 marks. Copy the error text from Monitor → Error Details and describe the fix if a partner really sent that payload.

Flatten XML back into a CSV report

XML to CSV20 min20 marks

Going out to a file share means flattening. Here you point the converter at the repeating element yourself — no schema needed.

XML to CSV Converter · configuration
Field	Value
Path to Source Element	/Orders/Order
Field Separator	,
Include Field Names as Headers	tick it

Then probe the limit · 8 marks. Wrap a nested element inside one <Order> and send it again. Report what happened to the nested data and why a CSV row cannot represent it.

Three broken payloads, three diagnoses

25 min15 marks

Every one of these arrives in real projects most weeks. Telling them apart from the symptom is the skill this lab builds.

Case A — the extra row. Send one CSV row and count the <Order> elements. Fix it in the converter.
Case B — the European export. Send a semicolon-separated row and see where values land.
Case C — the missing column. Send a row with only five values and decide if the result is acceptable.

VerifyCases A and B are configuration fixes inside the CSV converter. Case C is the interesting one — decide what you would do about it in a production interface.

Read this before you get stuck

Where beginners lose an hour

ORDER

CSV to XML maps by position, not by name.
The first column goes into the first XSD element, whatever either is called. A column added mid-file silently shifts every value after it.

ARRAY

One repeating record produces no JSON array.
Test every interface with one record and with many — not only with many.

ROOT

JSON to XML needs exactly one root member.
Two keys at the top level cannot become one XML root. Reshape before the converter.

CTYPE

A converter does not touch Content-Type.
Your payload is JSON but the header still says XML until you set it in a Content Modifier.

Self-check

Before you submit

01Partner sends CSV, receiver wants JSON. How many converters, in what order?

Two: CSV to XML, then XML to JSON. Every converter has XML on one side — XML is the hub.

02The same interface works with 50 rows and breaks on 1 row. Why?

One record → single occurrence → XML to JSON emits an object, not an array. The API expects [ ] and gets { }.

03Which converter needs no schema and no XPath at all?

JSON to XML — JSON already carries its own structure.

Hand-in

Submission checklist

Your field inventory of the CSV to XML Converter (Task 1) Both JSON responses from Task 2 — three rows and one row — plus your explanation The error text from the broken JSON payload (Task 3) CSV output with headers and without (Task 4) Cases A, B, C: symptom, cause, fix (Task 5)

Resources

Payloads for this lab

Task 1 · POST this text/csv

SO-100234,2026-09-01,CUST-8891,BIKE-RD-54,2,899.00
SO-100234,2026-09-01,CUST-8891,HELM-BLK-M,2,79.50
SO-100235,2026-09-02,CUST-4410,BIKE-GR-56,1,1249.00

Orders.xsd · add to the flow resources

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="Orders"><xs:complexType><xs:sequence>
    <xs:element name="Order" maxOccurs="unbounded"><xs:complexType><xs:sequence>
      <xs:element name="OrderNumber" type="xs:string"/>
      <xs:element name="OrderDate"   type="xs:string"/>
      <xs:element name="CustomerId"  type="xs:string"/>
      <xs:element name="Sku"         type="xs:string"/>
      <xs:element name="Quantity"    type="xs:string"/>
      <xs:element name="NetPrice"    type="xs:string"/>
    </xs:sequence></xs:complexType></xs:element>
  </xs:sequence></xs:complexType></xs:element>
</xs:schema>

Discussion

Compare your diagnoses

Task 5 has three right-ish answers — post yours and see how others fixed the European export.

Open the Integration Nest community →

Nest Labs · SAP Cloud IntegrationBeginner · ~120 min