func begin()

in pkg/tm/transaction_executor.go [99:151]
37 lines of code
13 McCabe index (conditional complexity)

func begin(ctx context.Context, gc *GtxConfig) error {
	switch pg := gc.Propagation; pg {
	case NotSupported:
		// If transaction is existing, suspend it
		// return then to execute without transaction
		if IsGlobalTx(ctx) {
			// because each global transaction operation will use a new context,
			// there is no need to implement a suspend operation, just unbind the xid here.
			// the same is true for the following case that needs to be suspended.
			UnbindXid(ctx)
		}
		return nil
	case Supports:
		// if transaction is not existing, return then to execute without transaction
		// else beginNewGtx transaction then return
		if IsGlobalTx(ctx) {
			useExistGtx(ctx, gc)
		}
		return nil
	case RequiresNew:
		// if transaction is existing, suspend it, and then Begin beginNewGtx transaction.
		if IsGlobalTx(ctx) {
			UnbindXid(ctx)
		}
	case Required:
		// default case, If current transaction is existing, execute with current transaction,
		// else continue and execute with beginNewGtx transaction.
		if IsGlobalTx(ctx) {
			useExistGtx(ctx, gc)
			return nil
		}
	case Never:
		// if transaction is existing, throw exception.
		if IsGlobalTx(ctx) {
			return fmt.Errorf("existing transaction found for transaction marked with pg 'never', xid = %s", GetXID(ctx))
		}
		// return then to execute without transaction.
		return nil
	case Mandatory:
		// if transaction is not existing, throw exception.
		// else execute with current transaction.
		if IsGlobalTx(ctx) {
			useExistGtx(ctx, gc)
			return nil
		}
		return fmt.Errorf("no existing transaction found for transaction marked with pg 'mandatory'")
	default:
		return fmt.Errorf("not supported propagation:%d", pg)
	}

	// the follow will to construct a new transaction with xid.
	return beginNewGtx(ctx, gc)
}