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Branching Paths

When processing data, you often need to take different actions based on intermediate results. This example shows how to create a legacy workflow that splits into separate paths, where each path executes different steps based on the output of a previous step.

Control Flow Diagram​

This example shows how to create a legacy workflow that splits into separate paths, where each path executes different steps based on the output of a previous step.

Here's the control flow diagram:

Diagram showing workflow with branching paths

Creating the Steps​

Let's start by creating the steps and initializing the workflow.

import { LegacyStep, LegacyWorkflow } from "@mastra/core/workflows/legacy";
import { z } from "zod"

const stepOne = new LegacyStep({
  id: "stepOne",
  execute: async ({ context }) => ({
    doubledValue: context.triggerData.inputValue * 2
  })
});

const stepTwo = new LegacyStep({
  id: "stepTwo",
  execute: async ({ context }) => {
    const stepOneResult = context.getStepResult<{ doubledValue: number }>("stepOne");
    if (!stepOneResult) {
      return { isDivisibleByFive: false }
    }

    return { isDivisibleByFive: stepOneResult.doubledValue % 5 === 0 }
  }
});


const stepThree = new LegacyStep({
  id: "stepThree",
  execute: async ({ context }) =>{
    const stepOneResult = context.getStepResult<{ doubledValue: number }>("stepOne");
    if (!stepOneResult) {
      return { incrementedValue: 0 }
    }

    return { incrementedValue: stepOneResult.doubledValue + 1 }
  }
});

const stepFour = new LegacyStep({
  id: "stepFour",
  execute: async ({ context }) => {
    const stepThreeResult = context.getStepResult<{ incrementedValue: number }>("stepThree");
    if (!stepThreeResult) {
      return { isDivisibleByThree: false }
    }

    return { isDivisibleByThree: stepThreeResult.incrementedValue % 3 === 0 }
  }
});

// New step that depends on both branches
const finalStep = new LegacyStep({
  id: "finalStep",
  execute: async ({ context }) => {
    // Get results from both branches using getStepResult
    const stepTwoResult = context.getStepResult<{ isDivisibleByFive: boolean }>("stepTwo");
    const stepFourResult = context.getStepResult<{ isDivisibleByThree: boolean }>("stepFour");

    const isDivisibleByFive = stepTwoResult?.isDivisibleByFive || false;
    const isDivisibleByThree = stepFourResult?.isDivisibleByThree || false;

    return {
      summary: `The number ${context.triggerData.inputValue} when doubled ${isDivisibleByFive ? 'is' : 'is not'} divisible by 5, and when doubled and incremented ${isDivisibleByThree ? 'is' : 'is not'} divisible by 3.`,
      isDivisibleByFive,
      isDivisibleByThree
    }
  }
});

// Build the workflow
const myWorkflow = new LegacyWorkflow({
  name: "my-workflow",
  triggerSchema: z.object({
    inputValue: z.number(),
  }),
});

Branching Paths and Chaining Steps​

Now let's configure the legacy workflow with branching paths and merge them using the compound .after([]) syntax.

// Create two parallel branches
myWorkflow
  // First branch
  .step(stepOne)
  .then(stepTwo)

  // Second branch
  .after(stepOne)
  .step(stepThree)
  .then(stepFour)

  // Merge both branches using compound after syntax
  .after([stepTwo, stepFour])
  .step(finalStep)
  .commit();

const { start } = myWorkflow.createRun();

const result = await start({ triggerData: { inputValue: 3 } });
console.log(result.steps.finalStep.output.summary);
// Output: "The number 3 when doubled is not divisible by 5, and when doubled and incremented is divisible by 3."

Advanced Branching and Merging​

You can create more complex workflows with multiple branches and merge points:

const complexWorkflow = new LegacyWorkflow({
  name: "complex-workflow",
  triggerSchema: z.object({
    inputValue: z.number(),
  }),
});

// Create multiple branches with different merge points
complexWorkflow
  // Main step
  .step(stepOne)

  // First branch
  .then(stepTwo)

  // Second branch
  .after(stepOne)
  .step(stepThree)
  .then(stepFour)

  // Third branch (another path from stepOne)
  .after(stepOne)
  .step(
    new LegacyStep({
      id: "alternativePath",
      execute: async ({ context }) => {
        const stepOneResult = context.getStepResult<{ doubledValue: number }>(
          "stepOne",
        );
        return {
          result: (stepOneResult?.doubledValue || 0) * 3,
        };
      },
    }),
  )

  // Merge first and second branches
  .after([stepTwo, stepFour])
  .step(
    new LegacyStep({
      id: "partialMerge",
      execute: async ({ context }) => {
        const stepTwoResult = context.getStepResult<{
          isDivisibleByFive: boolean;
        }>("stepTwo");
        const stepFourResult = context.getStepResult<{
          isDivisibleByThree: boolean;
        }>("stepFour");

        return {
          intermediateResult: "Processed first two branches",
          branchResults: {
            branch1: stepTwoResult?.isDivisibleByFive,
            branch2: stepFourResult?.isDivisibleByThree,
          },
        };
      },
    }),
  )

  // Final merge of all branches
  .after(["partialMerge", "alternativePath"])
  .step(
    new LegacyStep({
      id: "finalMerge",
      execute: async ({ context }) => {
        const partialMergeResult = context.getStepResult<{
          intermediateResult: string;
          branchResults: { branch1: boolean; branch2: boolean };
        }>("partialMerge");

        const alternativePathResult = context.getStepResult<{ result: number }>(
          "alternativePath",
        );

        return {
          finalResult: "All branches processed",
          combinedData: {
            fromPartialMerge: partialMergeResult?.branchResults,
            fromAlternativePath: alternativePathResult?.result,
          },
        };
      },
    }),
  )
  .commit();




View source on GitHub

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Workflows (Legacy)​

The following links provide example documentation for legacy workflows:

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