Top 50 DataWeave Interview Questions

Few of the changes from Dataweave 1.0 of Mule 3 to Dataweave 2.0 of Mule 4.

• Header changes (%dw 1.0 to %dw 2.0)
• Body changes
• Conditional logics (earlier it was when-otherwise and now its if-else)
• Function and Variable syntax
• Comments and many more

p() function is used to read the data from properties files such as http host, API Keys, database passwords etc.,

%dw 2.0
output application/json
---
{
    "Application Name": p('app.name')
  
}

We can use lookup() to invoke or call the flows from DataWeave. For example, lookup("anotherFlow", payload) executes a flow named anotherFlow and pass the payload to anotherFlow.

%dw 2.0
output application/json
---
{
    Mule: lookup('flow2', {test:'hello'}
}

Note: You can call only flows but not sub-flows.

• map iterates over an array and returns an array
• mapObject iterates over an object and returns an object
• pluck iterates over an object and returns an array of keys, values, or indices in that object.

We need to use secure:: prefix to access secure properties. for example,

%dw 2.0
output application/json
---
{
    "ClientSecret" : p('secure::api.clientSecret')
}

We can use flatten keyword to merge two arrays into single array. for example,

%dw 2.0
output application/json
---
flatten(payload..*payload)

%dw 2.0
output application/json
var myname = ['Max']
var yourname = ['Mule']
var ourname = [myname,yourname]
---
flatten(ourname)

Output:

[
 "Max", "Mule"
 ]

• flatMap iterates over each item in an array and flattens the results, can act on values and indices of items in the array.
• flatten turns a nested array into a simple array. only acts on the values of the arrays

%dw 2.0
output application/json
---
[ [3,5], [0.9,5.5] ] flatMap (value, index) -> value

Output:

[ 3, 5, 0.9, 5.5]

%dw 2.0
output application/json
var myname = ['Max']
var yourname = ['Mule']
var ourname = [myname,yourname]
---
flatten(ourname)

Output:

["Max", "Mule"]

We can use as Number to convert string to number in DataWeave. for example,

%dw 2.0
output application/json
---
"Price" : "345.60" as Number

Output:

{ "Price" : 345.60 }

• $$ symbol is used to access the key (or index) of the key-value pair. In an array it returns index and in object it returns key.
• $ symbol is used to access the value of the key-value pair.

%dw 2.0
output application/json
var myname =
 { "name": "Max" }		
---
myname mapObject {
	key: $$,
	value: $
}

Output:

{
  "key": "name",
  "value": "Max"
}

We can use map functions to map Objects elements as an array. for example,

%dw 2.0
output application/json
var BookShop = {
  "inventory": {
      "book" : {
        "title": "Everyday Italian",
        "author": "Giada De Laurentiis",
        "year": "2005",
        "price": "30.00"
      },
      "book" :{
        "title": "Harry Potter",
        "author": "J K. Rowling",
        "year": "2005",
        "price": "29.99"
      }
}}
---
items: BookShop.inventory.*book map (item, index) -> {
      "type": "book",
      "Id": index,
      "title": item.title,
      "author": item.author,
      "year": item.year,
      "price": item.price as Number
      
}
 

Output:

{
  "items": [
    {
      "type": "book",
      "Id": 0,
      "title": "Everyday Italian",
      "author": "Giada De Laurentiis",
      "year": "2005",
      "price": 30.00
    },
    {
      "type": "book",
      "Id": 1,
      "title": "Harry Potter",
      "author": "J K. Rowling",
      "year": "2005",
      "price": 29.99
    }
  ]
}

We can use now() function to log the current time.

%dw 2.0
output application/json		
---
{
    "transactionTime" : now()
}

We can use skipNullOn to skip the null values. It will skip the NULL value fields.

%dw 2.0
output application/json skipNullOn="everywhere"
---
{
	"name": "NaGG",
	"company": "MuleSoft",
	"designation": null
}
 

{
	"name": "NaGG"
,
	"company": "MuleSoft"
}
 

We can use zip() function to merge two arrays into an array of arrays. for example,

%dw 2.0
output application/json
---
{
	"empDetails" : ["NaGG","Joe"] zip ["Integration Engineer", "Integration Lead"]
}
 
 

We can use mask operator to mask the sensitive information. for example,

%dw 2.0
output application/json
import * from dw::util::Values
var personal ={
	"name": "NaGG",
	"ssn": "ABCD1234",
	"company": "MuleSoft"
}
---
(personal mask "ssn" with "****") mask "password" with "****"
 
 

{
  "name": "NaGG",
  "ssn": "****",
  "company": "MuleSoft"
}
 
 

We can use - to remove specific key:value pairs. for example,

%dw 2.0
output application/json
var details = {
	"name": "NaGG",
	"ssn": "ABCD1234",
	"company": "MuleSoft",
	"age": "25 Years"
}
---

{
	empDetails : details - "age"
}
 

{
  "empDetails": {
    "name": "NaGG",
    "ssn": "ABCD1234",
    "company": "MuleSoft"
  }
}
 
 

We can use log() function to log the input as system log. for example,

%dw 2.0
output application/json
---

log ("WISHES", "All the Best Mate")

WISHES - "All the Best Mate"

• match uses regex to match a string and then separates it into capture groups. Returns the results in an array.
• matches checks if an expression matches the entire input string and returns Boolean vaue.

match:

%dw 2.0
output application/json
---
"[email protected]" match(/([a-z]*)@([a-z]*).com/)

Output:

[
  "[email protected]",
  "me",
  "mulesoft"
]

matches:

%dw 2.0
output application/json
---
[ ("admin123" matches /a.*\d+/), ("admin123" matches /^b.+/) ]

Output:

[ true, false ]

• read () reads the a string or binary and returns parsed content.
• readUrl() Reads a URL, including a classpath-based URL, and returns parsed content.

read:

%dw 2.0
output application/xml
---
read('{ "Hello" : "Vanchiv" }','application/json')

<?xml version='1.0' encoding='UTF-8' ?>
<Hello>Vanchiv</Hello>

readUrl:

%dw 2.0
output application/json
---
readUrl("https://jsonplaceholder.typicode.com/posts/1", "application/json")

 "userId": 1, "id": 1, "title": "sunt aut", "body": "quia et" }

The major difference is read() function reads the string or binary whereas readUrl() reads a URL (including classpath)

reduce can be used to process an :array and operate on each of its elements. It performs an aggregation operation on the elements of the array after performing a lambda operation (optional) on each of its element. for example,

read:

%dw 2.0
output application/json
var numbers =[1,2,3,4]
---
{
	sum : numbers reduce ($$ + $),
	concat: numbers reduce ($$ ++ $)
}

Output:

{
  "sum": 10,
  "concat": "1234"
}

• sizeOf() returns no of elements in an array and no of key-value pairs in an object.
• typeOf() returns the data type of given input. such as array, object, string etc.,

sizeOf():

%dw 2.0
output application/json
var numbers =[1,2,3,4]
---
sizeOf(numbers)

Output:

4

sizeOf():

%dw 2.0
output application/json
var numbers =[1,2,3,4]
---
typeOf(numbers)

Output:

"Array"

Splits a string into a string array based on a value that matches part of that string. It filters out the matching part from the returned array.

%dw 2.0
output application/json
var name = "Max-Mule"
---
name splitBy("-")

Output:

[ "Max",
"Mule"
]

We can use trim() function to remove any blank spaces from the beginning and end of a string.

%dw 2.0
output application/json
---

trim("     Welcome to Vanchiv    ")

Output:

"Welcome to Vanchiv"

Note: It won’t remove any spaces from the middle of the string, only the beginning and end

We can se toBase64() and fromBase64() functions to encode and decode a string. for example,

%dw 2.0
output application/json
import dw::Crypto
import toBase64 from dw::core::Binaries
import fromBase64 from dw::core::Binaries
var encode = "Secret"
var decode = "U2VjcmV0"
---

{
	encyption: toBase64(encode),
	decryption: fromBase64(decode)
}

Output:

{
  "encyption": "U2VjcmV0",
  "decryption": "Secret"
}

%dw 2.0
output application/json
var number = attributes.queryParams.number
var result = number mod 2
---

   if (result == 0)
      { number: "Even" }
   else {  number: "Odd" }