Flow Control and Scope Operations in DataWeave
Introduction
You can use the following operators within any DataWeave expression:
do
A “do” statement allows you to create a specific area where you can declare and use new variables, functions, annotations, or namespaces. It is structured like a map, with a header and a body separated by —. The header is where you define all the things you want to declare, and the body represents the result of the expression.
This example uses do to return the string “DataWeave” when myfun() is called from the main body of the script.
DataWeave Script:
%dw 2.0
output application/json
fun myfun() = do {
var name = “DataWeave”
—
name
}
—
{ result: myfun() }
This example uses do to return the string “DataWeave” when the variable myVar is referenced from the main body of the script.
DataWeave Script:
%dw 2.0
output application/json
var myVar = do {
var name = “DataWeave”
—
name
}
—
{ result: myVar }
Both scripts produce this output:
Output:
{
“result”: “DataWeave”
}
if else
An “if” statement checks whether a condition is true or false. If the condition is true, it executes the code inside the “if” block. If the condition is false, it executes the code inside the “else” block. Each “if” statement must have a corresponding “else” statement.
Here’s an example that uses the input { country : “FRANCE” }, defined as the variable “myVar” in the header:
DataWeave Script:
%dw 2.0
var myVar = { country : “FRANCE” }
output application/json
—
if (myVar.country == “USA”)
{ currency: “USD” }
else { currency: “EUR” }
Output:
{
“currency”: “EUR”
}
You can use the if-else construct with various types of conditions that result in true or false. This includes mathematical, logical, equality, and relational statements. The condition can be applied to any valid input.
The following DataWeave script applies if-else statements to the outcome of certain conditional statements:
- A mathematical operation in ex1
The if else statement returns the Boolean value true if the operation 1 + 1 == 55 is true and false if not. - An equality operation in ex2
The if else statement returns 1 if the value of the specified index is 1 or a string if the value is not 1. - An isEmpty function in ex3
The if else statement returns the string “ID is empty” or “ID is not empty” depending on whether aRecord.bookId contains a value. - A mapping in ex4 that iterates over firstInput
The if else statement returns the value of the bookId as a Number if the value is equal to 101. It returns the specified string if the value is not equal to 101.
DataWeave Script:
%dw 2.0
var aRecord =
[
“bookId”:”101″,
“title”:”world history”,
“price”:”19.99″
]
output application/xml
—
{ examples:
{
ex1 : if (1 + 1 == 55) true
else false,
ex2 : if ([1,2,3,4][1] == 1) 1
else “value of index 1 is not 1”,
ex3 : if (isEmpty(aRecord.bookId)) “ID is empty”
else “ID is not empty”,
ex4 : aRecord.bookId map (idValue) ->
if (idValue as Number == 101) idValue as Number
else “not 101”
}
}
Output:
<?xml version=’1.0′ encoding=’UTF-8′?>
<examples>
<ex1>false</ex1>
<ex2>value of index 1 is not 1</ex2>
<ex3>ID is not empty</ex3>
<ex4>101</ex4>
</examples>
else if
In this example, the “if-else” construct is used to chain multiple “else if” expressions together. The input variable “myVar” is defined as { country: “UK” }. This structure allows for conditional checks on the value of the “country” field. If the condition matches the value “USA,” a specific code block is executed. If none of the conditions are met, the code in the final “else” block is executed.
DataWeave Script:
%dw 2.0
var myVar = { country : “UK” }
output application/json
—
if (myVar.country ==”USA”)
{ currency: “USD” }
else if (myVar.country ==”UK”)
{ currency: “GBP” }
else { currency: “EUR” }
Output
{
“currency”: “GBP”
}
The following example is similar but takes an array as input instead of an object. The body of the script uses if else and else if statements within a do operation to populate the value of the hello variable.
DataWeave Script:
%dw 2.0
output application/json
—
[“Argentina”, “USA”, “Brazil”] map (country) -> do {
var hello = if(country == “Argentina”) “Hola”
else if(country == “USA”) “Hello”
else if(country == “Brazil”) “Ola”
else “Sorry! We don’t know $(country)’s language.”
—
“$(hello) DataWeave”
}
Output:
[
“Hola DataWeave”,
“Hello DataWeave”,
“Ola DataWeave”
]
Reference
