BRANCH Step

The BRANCH step enables conditional logic in your flows. It allows the ESB to choose different execution paths based on the values currently in the pipeline.

Properties

Property	Type	Description
type	string	Must be branch.
switch	string	(Optional) The pipeline variable to evaluate for Switch Mode.
cases	object	A map where keys are values or conditions, and values are arrays of steps.

---

Mode 1: Switch Mode (Value Matching)

Use Switch Mode when you want to compare a single variable against multiple possible values. This is equivalent to a switch or match statement in code.

• Specify the variable in the switch property (e.g., switch: "${status}").
• In cases, the keys are the literal values to match.

- type: "branch"
  switch: "${paymentMethod}"
  cases:
    "credit_card":
      - type: "invoke"
        service: "payments:ProcessCreditCard"
    "paypal":
      - type: "invoke"
        service: "payments:ProcessPaypal"
    "$default":
      - type: "exit"
        message: "Unsupported payment method"

---

Mode 2: Expression Mode (Condition Matching)

Use Expression Mode for more complex logic involving multiple variables or numeric comparisons.

• Leave the switch property empty.
• In cases, the keys are conditional expressions.
• The engine evaluates cases sequentially. The first case that evaluates to true is executed.

Supported Operators

• Equality: ==, !=
• Comparison: >, <, >=, <=

Example: Scoring Logic

- type: "branch"
  cases:
    "${score} >= 90":
      - type: "map"
        set:
          grade: "A"
    "${score} >= 80":
      - type: "map"
        set:
          grade: "B"
    "$default":
      - type: "map"
        set:
          grade: "F"

---

The $default Case

Both modes support a special $default case. This case is executed only if no other cases match. It is highly recommended to include a $default case to handle unexpected data.

Example: Expression Branching

Step Definition

- name: "EvaluateScore"
  type: "branch"
  cases:
    "${score} >= 90":
      - type: "map"
        set:
          grade: "Excellent"
    "${score} >= 60":
      - type: "map"
        set:
          grade: "Pass"
    "$default":
      - type: "map"
        set:
          grade: "Fail"

Data Flow Scenario: Passing Score

Initial Pipeline:

{
  "student": "Alice",
  "score": 85
}

Resulting Pipeline:

{
  "student": "Alice",
  "score": 85,
  "grade": "Pass"
}

Data Flow Scenario: Default Case

Initial Pipeline:

{
  "student": "Bob",
  "score": 45
}

Resulting Pipeline:

{
  "student": "Bob",
  "score": 45,
  "grade": "Fail"
}

Tips

• Switch for Clarity: If you are just checking one variable, Switch Mode is cleaner and more readable.
• Order Matters: In Expression Mode, the order of cases is critical. Put the most specific conditions first.
• Empty Branch: If no case matches and there is no $default, the branch step simply does nothing and moves to the next step in the flow.