Complex data models with Chaincode and Go

The basic examples with Hyperledger are excellent but I wanted to model a data structure with optional and repeating elements. Using Chaincode I then wanted to create and read a record.

The use case for this type of problem is a common one. In your list of contacts a typical contact would have multiple email telephone numbers and it is not possible to know in advance how many phone numbers any particular contact may have. They may have no phone number, one phone or many phone numbers.

The notation to use in Chaincode is []*

[] — means this repeats

* — means this is optional, so may or may not appear

type Contact stuct {

ContactID int `json:”contactid”`

Fullname string `json:”fullname”`

Telephone []*Tele `json:”tele”`

}

type Tele struct {

Teletype string `json:”type”`

Telephonenumber string `json:”telenum”`

}

To write to the Hyperledger Fabric blockchain using Go Chaincode the following code looks like this.

func (s *ComplexContract) NewContact(ctx contractapi.TransactionContextInterface, contactid string, fullname string, , tele []*Tele) error {

//create a new contact

ca := new(Contact)

ca.ContactID = contactid

ca.Fullname = fullname

ca.Telephone = tele

//transform into a JSON document

caBytes, _ := json.Marshal(ca)

//Create contact

err := ctx.GetStub().PutState(contactid, []byte(caBytes))

return nil

}

The arguments to call to the contract are as follows

Example 1

‘{“Args”:[“NewContact”,”CONTACT_001”,”Jane Doe”,“[{“Mobile”,”555–555–555”},{“Work”, “555–666–777”}]”]}’

This will create a contact called Jane Doe with two telephone numbers

Example 2

‘{“Args”:[“NewContact”,”CONTACT_002”,”Jim Doe”,“[]”]}’

This will create a contact called Jim Doe without telephone numbers (No one likes Jim :-))

Example 3

‘{“Args”:[“NewContact”,”CONTACT_003”,”Joe Doe”,“[{“Work”, “444–666–777”}]”]}’

This will create a contact called Joe Doe with one telephone number