Data not persisting

Question

I have a solidity contract that allows users to register a name to their address. This is done with the register function. I also have a function to allow users to check the availability of a name; checkAvailability.

The problem is that checkAvailability never returns false. It's as if the users mapping never saves any values. Does anyone have any suggestions?

pragma solidity ^0.4.4;

contract Users {
    mapping (bytes32 => address) public users;

    function register(bytes32 name) {
        if(users[name] == 0 && name != ""){
            users[name] = msg.sender;
        }
    }

    function checkAvailability(bytes32 name) returns (bool) {
      if(users[name] == 0) {
        return true;
      }
      return false;
    }

}

NOTES: Checking against 0x00 doesn't seem to fix the issue. I'm using truffle test file to test this contract:

 it.only("should user", function() {
    return Users.deployed().then(function(instance) {
      return instance.register.call('test')
        .then(() => {
          return instance.checkAvailability.call('test');
        });
    })
    .then((register) => {
      console.log(register);
    });
  });

Answer 1

Solution was to call register with instance.register('foo', { from: acccounts[0] }) then instance.checkAvailability.call('hi') will return false.

... no idea why.

EDIT: Found out why! There is a difference between transactions and local calls: What is the difference between a transaction and a call?

Answer 2

there is the solution : i suggest to compare the address with 0X0 not with 0

 pragma solidity ^0.4.4;

contract Users {
    mapping (bytes32 => address) public users;

    function register(bytes32 name) {
        if(users[name] == 0x0 && name != ""){
            users[name] = msg.sender;

        }
    }

    function checkAvailability(bytes32 name) returns (bool) {
      if(users[name] == 0x0) {
        return true;
      }
      return false;
    }

}