Just like any other programming language, In Mule4, dataweave provides matchfunction to achieve the functionality of if-else statements. 

A match expression contains a list of case statements that can optionally have an else statement. Each case statement consists of a conditional selector expression that must evaluate to either true or false.

Pattern matching is another method of flow control, but it does quite a bit more under the hood than the if/else expression does, and the syntax is a little more complicated. Like the if/else expression, pattern matching also returns a single value. Here’s a simplification of how pattern matching expressions are formatted:

Let’s consider a scenario where you need to update certain fields of incoming payload keeping the rest of the fields as it is, you can use a match and case.

match Statement Syntax:

<input_expression> match {
  case <condition> -> <execute_if_condition_pass>
  case <condition> -> <execute_if_condition_pass>
  else -> <execute_if_no_condition_pass>
}

inputExpression match {
  case <condition> -> <routing expression>
  case <condition> -> <routing expression>
  else -> <default routing expression>
}

The easiest way to understand basic pattern matching it to show an example:

---

Input:

{
  "action": "buy"
}

DW Script:

%dw 2.0
output json
---
payload.action match {
  case "buy"  -> “Buy at market price"
  case "sell" -> "Sell at market price"
  case "hold" -> “Hold asset"
  else   -> "Invalid input"
}

Output:

"Buy at market price"

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