example.go

func (s *SmartContract) CreateAsset(ctx contractapi.TransactionContextInterface, id string, color string, size int, owner string, appraisedValue int) error {
    exists, err := s.AssetExists(ctx, id)
    if err != nil {
        return err
    }
    if exists {
        return fmt.Errorf("the asset %s already exists", id)
    }

    asset := Asset{
        ID:             id,
        Color:          color,
        Size:           size,
        Owner:          owner,
        AppraisedValue: appraisedValue,
    }
    assetJSON, err := json.Marshal(asset)
    if err != nil {
        return err
    }

    return ctx.GetStub().PutState(id, assetJSON)
}