DataWeave Functions: Learn From Basics and Simplicity (Dev’s Choice)

In this article, learn some basic and useful functions of DataWeave 2.0 (Developer's choice) in MuleSoft for integrations.

Nitish Jain

May. 31, 24 · Tutorial

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Hi Muleys!

In this post, we will be learning about basic and useful functions of DataWeave 2.0 with quick examples.

The list of functions used in the article below is selected out from the list of huge functions available in DataWeave(Developer's choice):

Join (join)
Left Join (leftJoin)
Outer Join (outerJoin)
Nested join with map operator
Update as Function
Update as Operator
Max By (maxBy)
Min By (minBy)
Filtering an array (filter)
Map an array (map)
DistinctBy an array (distinctBy)
GroupBy an array (groupBy)
Reduce an array (reduce)
Flatten an array (flatten)

We may or may not have used the DataWeave function in our daily integrations. Let's see the examples below for each function.

1. Join

The join function behaves similarly to a SQL database JOIN.
The join function combines elements of two arrays by matching two ID criteria for the same index in both arrays.
The left and right arrays must be arrays of objects.
Importing core::Arrays function is required.
Ignores unmatched objects

DataWeave Code

    Plain Text
   
 

   %dw 2.0
output application/json
import * from dw::core::Arrays
var a = [{"Name": "Ram","Billing City": "BLR","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 1000},{"Name": "Max","Billing City": "NY","Billing Country": "USA","Message": "Hello world!!","Type": "Account","Allowance": 2000}]
var b = [{"Name": "Shyam","Billing City": "HYD","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 3000}]
---
//join(a, b,  (emp) -> emp."Billing Country", (loc)-> loc."Billing Country")
//join(a,b, (a)-> a."Billing Country", (b)-> b."Billing Country")
join(a,b, (x)-> x."Billing Country", (y)-> y."Billing Country")
  

Output:

    JSON
   
 

   [
  {
    "l": {
      "Name": "Ram",
      "Billing City": "BLR",
      "Billing Country": "India",
      "Message": "Hello world!",
      "Type": "Account",
      "Allowance": 1000
    },
    "r": {
      "Name": "Shyam",
      "Billing City": "HYD",
      "Billing Country": "India",
      "Message": "Hello world!",
      "Type": "Account",
      "Allowance": 3000
    }
  }
]
  

2. Left Join

All the joined objects are returned.
Importing core::Arrays function is required.
Any unmatched left elements are also added.

DataWeave Code

    Plain Text
   
 

   %dw 2.0
output application/json
import * from dw::core::Arrays
var a = [{"Name": "Ram","Billing City": "BLR","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 1000},{"Name": "Max","Billing City": "NY","Billing Country": "USA","Message": "Hello world!!","Type": "Account","Allowance": 2000}]
var b = [{"Name": "Shyam","Billing City": "HYD","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 3000}]
---
leftJoin(a,b, (x)-> x."Billing Country", (y)-> y."Billing Country")
  

Output:

    JSON
   
 

   [
  {
    "l": {
      "Name": "Ram",
      "Billing City": "BLR",
      "Billing Country": "India",
      "Message": "Hello world!",
      "Type": "Account",
      "Allowance": 1000
    },
    "r": {
      "Name": "Shyam",
      "Billing City": "HYD",
      "Billing Country": "India",
      "Message": "Hello world!",
      "Type": "Account",
      "Allowance": 3000
    }
  },
  {
    "l": {
      "Name": "Max",
      "Billing City": "NY",
      "Billing Country": "USA",
      "Message": "Hello world!!",
      "Type": "Account",
      "Allowance": 2000
    }
  }
]
  

3. Outer Join

All the joined objects are returned.
Importing the core::Arrays function is required.
Any unmatched left element or right elements are also added.

DataWeave Code

    Plain Text
   
 

   %dw 2.0
output application/json
import * from dw::core::Arrays
var a = [{"Name": "Ram","Billing City": "BLR","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 1000},{"Name": "Max","Billing City": "NY","Billing Country": "USA","Message": "Hello world!!","Type": "Account","Allowance": 2000}]
var b = [{"Name": "Shyam","Billing City": "HYD","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 3000}]
---
outerJoin(a,b, (x)-> x."Billing Country", (y)-> y."Billing Country")
  

Output:

    JSON
   
 

   [
  {
    "l": {
      "Name": "Ram",
      "Billing City": "BLR",
      "Billing Country": "India",
      "Message": "Hello world!",
      "Type": "Account",
      "Allowance": 1000
    },
    "r": {
      "Name": "Shyam",
      "Billing City": "HYD",
      "Billing Country": "India",
      "Message": "Hello world!",
      "Type": "Account",
      "Allowance": 3000
    }
  },
  {
    "l": {
      "Name": "Max",
      "Billing City": "NY",
      "Billing Country": "USA",
      "Message": "Hello world!!",
      "Type": "Account",
      "Allowance": 2000
    }
  }
]
  

4. Nested Join With Map Operator

Use the map function to iterate over each joined object.
Importing the core::Arrays function is required.

DataWeave Code

    Plain Text
   
 

   %dw 2.0
output application/json
import * from dw::core::Arrays
var a = [{"Name": "Ram","Billing City":"BLR","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 1000},{"Name": "Max","Billing City": "NY","Billing Country": "USA","Message": "Hello world!!","Type": "Account","Allowance": 2000}]
var b = [{"Name": "Shyam","Billing City":"HYD","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 3000}]
---
(join(a,b, (x)-> x."Billing Country", (y)-> y."Billing Country"))
map {
    "info": $.l ++ $.r - "Billing Country"
}
  

Output:

    JSON
   
 

   [
  {
    "info": {
      "Name": "Ram",
      "Billing City": "BLR",
      "Billing Country": "India",
      "Message": "Hello world!",
      "Type": "Account",
      "Allowance": 1000,
      "Name": "Shyam",
      "Billing City": "HYD",
      "Message": "Hello world!",
      "Type": "Account",
      "Allowance": 3000
    }
  }
]
  

5. Update as Function

For Fieldname

This update function updates a field in an object with the specified string value.
The function returns a new object with the specified field and value.
Introduced in DataWeave version 2.2.2
Importing the util::Values function is required.

DataWeave Code

    Plain Text
   
 

   %dw 2.0
output application/json
import * from dw::core::Arrays
import * from dw::util::Values
var a = [{"Name": "Ram","Billing City": "BLR","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 1000},{"Name": "Max","Billing City": "NY","Billing Country": "USA","Message": "Hello world!!","Type": "Account","Allowance": 2000}]
var b = [{"Name": "Shyam","Billing City": "HYD","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 3000}]
fun mapping() = (if (isEmpty(a)) b else a)
var c = {"element": mapping()}
---
c update "element" with "abc"  //string
  

Output:

    JSON
   
   {
  "element": "abc"
}

For Index

Updates an array index with the specified value
This update function returns a new array that changes the value of the specified index.
Introduced in DataWeave version 2.2.2
Importing the util::Values function is required.

DataWeave Code

    Plain Text
   
 

   %dw 2.0
output application/json
import * from dw::core::Arrays
import * from dw::util::Values
var a = [{"Name": "Ram","Billing City": "BLR","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 1000},{"Name": "Max","Billing City": "NY","Billing Country": "USA","Message": "Hello world!!","Type": "Account","Allowance": 2000}]
var b = [{"Name": "Shyam","Billing City": "HYD","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 3000}]
fun mapping() = (if (isEmpty(a)) b else a)
var c = {"element": mapping()}
var d = [1, true, 2, 3, false]
---
d update 2 with 5  //index
  

Output:

    JSON
   
 

   [
  1,
  true,
  5,
  3,
  false
]
  

6. Update as Operator

This new update operator will update a specific field value with a new value given.
This feature adds an easy way to update single values in nested data structures without requiring to understand functional recursion.
No extra dw libraries are required.

DataWeave Code

    Plain Text
   
 

   %dw 2.0
output application/json
var a = [{"Name": "Ram","Billing City": "BLR","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 1000},{"Name": "Max","Billing City": "NY","Billing Country": "USA","Message": "Hello world!!","Type": "Account","Allowance": 2000}]
var b = [{"Name": "Shyam","Billing City": "HYD","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 3000}]
fun mapping() = (if (isEmpty(a)) b else a)
var c = {"element": mapping()}
var d = [1, true, 2, 3, false]
---
c update {
    case element at .element -> if (element == a) "Max" else "Mule"
}
  

Output:

    JSON
   
   {
  "element": "Max"
}

7. Max By

Iterates over an array and returns the highest value of comparable elements from it.
The items must be of the same type. maxBy throws an error if they are not, and the function returns null if the array is empty.

DataWeave Code

    Plain Text
   
 

   %dw 2.0
output application/json
var a = [{"Name": "Ram","Billing City": "BLR","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 1000},{"Name": "Max","Billing City": "NY","Billing Country": "USA","Message": "Hello world!!","Type": "Account","Allowance": 2000}]
var b = [{"Name": "Shyam","Billing City": "HYD","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 3000}]
fun mapping() = (if (isEmpty(a)) b else a)
var c = {"element": mapping()}

---
a maxBy $.Allowance
  

Output:

    JSON
   
 

   {
  "Name": "Max",
  "Billing City": "NY",
  "Billing Country": "USA",
  "Message": "Hello world!!",
  "Type": "Account",
  "Allowance": 2000
}
  

8. Min By

Iterates over an array to return the lowest value of comparable elements from it.
The items need to be of the same type. minBy returns an error if they are not, and it returns null when the array is empty.

DataWeave Code

    Plain Text
   
 

   %dw 2.0
output application/json
var a = [{"Name": "Ram","Billing City": "BLR","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 1000},{"Name": "Max","Billing City": "NY","Billing Country": "USA","Message": "Hello world!!","Type": "Account","Allowance": 2000}]
var b = [{"Name": "Shyam","Billing City": "HYD","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 3000}]
fun mapping() = (if (isEmpty(a)) b else a)
var c = {"element": mapping()}

---
a minBy $.Allowance
  

Output:

    JSON
   
 

   {
  "Name": "Ram",
  "Billing City": "BLR",
  "Billing Country": "India",
  "Message": "Hello world!",
  "Type": "Account",
  "Allowance": 1000
}
  

Input payload (common for all functions below)

    JSON
   
   [{"Name": "Ram","Billing City": "BLR","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 1000},
{"Name": "Max","Billing City": "NY","Billing Country": "USA","Message": "Hello world!!","Type": "Account","Allowance": 2000},
{"Name": "Shyam","Billing City": "HYD","Billing Country": "India","Message": "Hello world!","Type": "Account","Allowance": 3000},
{"Name": "John","Billing City": "FL","Billing Country": "USA","Message": "Hello world!!","Type": "Account","Allowance": 4000}]

9. Filtering an Array (filter)

To filter the data based on the condition.

DataWeave Code

    Plain Text
   
 

   %dw 2.0
output application/json
---
payload filter ((item, index) -> 
item."Billing Country" == "India"
)
  

Output:

    JSON
   
 

   [
  {
    "Name": "Ram",
    "Billing City": "BLR",
    "Billing Country": "India",
    "Message": "Hello world!",
    "Type": "Account"
  },
  {
    "Name": "Shyam",
    "Billing City": "HYD",
    "Billing Country": "India",
    "Message": "Hello world!",
    "Type": "Account"
  }
]
  

10. Map an Array (map)

Transforming every item in an array

DataWeave Code

    Plain Text
   
 

   %dw 2.0
output application/json
---
payload map ((item, index) -> 
{"Cities": if (item."Billing Country" == "USA") "USA" else "Others"}
)
  

Output:

    JSON
   
 

   [
  {
    "Cities": "Others"
  },
  {
    "Cities": "USA"
  },
  {
    "Cities": "Others"
  },
  {
    "Cities": "USA"
  }
]
  

11. DistinctBy an Array (distinctBy)

Remove duplicate items from an Array.

DataWeave Code

    Plain Text
   
 

   %dw 2.0
output application/json
---
payload distinctBy ((item, index) -> 
item."Billing Country"
)
  

Output:

    JSON
   
 

   [
  {
    "Name": "Ram",
    "Billing City": "BLR",
    "Billing Country": "India",
    "Message": "Hello world!",
    "Type": "Account"
  },
  {
    "Name": "Max",
    "Billing City": "NY",
    "Billing Country": "USA",
    "Message": "Hello world!!",
    "Type": "Account"
  }
]
  

12. GroupBy an Array (groupBy)

Grouping together items in an array based on some value

DataWeave Code

    Plain Text
   
 

   %dw 2.0
output application/json
---
payload groupBy ((item, index) -> 
item."Billing Country"
)
  

Output:

    JSON
   
 

   {
  "India": [
    {
      "Name": "Ram",
      "Billing City": "BLR",
      "Billing Country": "India",
      "Message": "Hello world!",
      "Type": "Account"
    },
    {
      "Name": "Shyam",
      "Billing City": "HYD",
      "Billing Country": "India",
      "Message": "Hello world!",
      "Type": "Account"
    }
  ],
  "USA": [
    {
      "Name": "Max",
      "Billing City": "NY",
      "Billing Country": "USA",
      "Message": "Hello world!!",
      "Type": "Account"
    },
    {
      "Name": "John",
      "Billing City": "FL",
      "Billing Country": "USA",
      "Message": "Hello world!!",
      "Type": "Account"
    }
  ]
}
  

13. Reduce an Array (reduce)

It can be used to transform an array to any other type.

DataWeave Code

    Plain Text
   
   %dw 2.0
output application/json
---
payload."Allowance" reduce ((item, accumulator) -> (item + accumulator))

Output:

    Plain Text
   
   10000

14. Flatten an Array (flatten)

DataWeave Code

    Plain Text
   
   %dw 2.0
output application/json
---
flatten (payload.Name)

Output:

    JSON
   
 

   [
  "Ram",
  "Max",
  "Shyam",
  "John"
]
  

Conclusion

As MuleSoft Developers, we use DataWeave codes almost daily in our integrations. The functions mentioned above of Array and examples could help us achieve our desired outputs/results easily.

Happy learning!

JSON Array data type MuleSoft

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DataWeave Functions: Learn From Basics and Simplicity (Dev’s Choice)

In this article, learn some basic and useful functions of DataWeave 2.0 (Developer's choice) in MuleSoft for integrations.

1. Join

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2. Left Join

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3. Outer Join

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4. Nested Join With Map Operator

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5. Update as Function

For Fieldname

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For Index

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6. Update as Operator

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7. Max By

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8. Min By

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9. Filtering an Array (filter)

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12. GroupBy an Array (groupBy)

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13. Reduce an Array (reduce)

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