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How to handle a Query in a Workflow in Go

Use the SetQueryHandler API from the go.temporal.io/sdk/workflow package to set a Query Handler that listens for a Query by name.

The handler must be a function that returns two values:

  1. A serializable result
  2. An error

The handler function can receive any number of input parameters, but all input parameters must be serializable. The following sample code sets up a Query Handler that handles the current_state Query type:

func MyWorkflow(ctx workflow.Context, input string) error {
currentState := "started" // This could be any serializable struct.
queryType := "current_state"
err := workflow.SetQueryHandler(ctx, queryType, func() (string, error) {
return currentState, nil
})
if err != nil {
currentState = "failed to register query handler"
return err
}
// Your normal Workflow code begins here, and you update the currentState as the code makes progress.
currentState = "waiting timer"
err = NewTimer(ctx, time.Hour).Get(ctx, nil)
if err != nil {
currentState = "timer failed"
return err
}
currentState = "waiting activity"
ctx = WithActivityOptions(ctx, myActivityOptions)
err = ExecuteActivity(ctx, MyActivity, "my_input").Get(ctx, nil)
if err != nil {
currentState = "activity failed"
return err
}
currentState = "done"
return nil
}

For example, suppose your query handler function takes two parameters:

err := workflow.SetQueryHandler(ctx, "current_state", func(prefix string, suffix string) (string, error) {
return prefix + currentState + suffix, nil
})