contract instance has a null transactionHash

Question

I have migrated the contract via truffle, code like this, very simple
and it returns the contract account address

[root@localhost c2]# truffle migrate
Compiling ./contracts/Ballot.sol...
Writing artifacts to ./build/contracts
Running migration: 1_initial_migration.js
  Replacing Ballot...
  Ballot: 0x2eb2128b3150bd4b95e96540b7e2d2151bcfb2cc
Saving successful migration to network...
Saving artifacts...

then I created the contract instance like this

myBallot = eth.contract(abi).at(addr)

abi and addr are vars, and they are certainly right, then

myBallot
{
  abi: [{
      constant: false,
      inputs: [{...}],
      name: "vote",
      outputs: [],
      payable: false,
      type: "function"
    }
    …………
  ],
  address: "0x071d808a15df658c0b39b71d127f4df05bb66abb",
  transactionHash: null,
  allEvents: function(),
  chairperson: function(),
  giveRightToVote: function(),
  proposals: function(),
  vote: function(),
  voteCast: function(),
  voters: function(),
  winnerName: function(),
  winningProposalIndex: function()
}

the transactionHash is null

and then I call the function myBallot.giveRightToVote(eth.accounts[0]); and continue minned, the voters is still empty

 myBallot.voters()
[false, 0, 0]

Answer 1

You're creating the contract instance with an address. You haven't told eth.contract anything about a transaction, so there's no reason why you should be seeing a transaction hash.