angularjs on form edit select option does not load value On Second Time - angularjs

Question

My form has got 2 select boxes. The second select options box is loaded when an option is selected in first box. The form is used for both adding and editing. I show the list below the form with edit button against each row. When I click on edit button it loads the values in form to edit. The thing is when I click on a row for first time it loads the values in form perfectly. If I click on another row button to edit, the SECOND select option alone does not show the selected value. But the box is loaded with values.
Code in controller:
$scope.editShift = function(row) {
for (var i = 0; i < $scope.availableShift.length; i++) {
if ($scope.availableShift[i].shiftId === row.entity.shiftId) {
$scope.shift = angular.copy($scope.availableShift[i]);
break;
};
};
$scope.selectLineNames();
};
$scope.selectLineNames = function(){
$scope.availableListOfLineNames = [];
$scope.availableListOfLineNamesTemp = LineDetails.ld_get_ln_resource.query
({plant: $scope.shift.plant}, function(response) {
angular.forEach(response, function(item) {
if (item) {
$scope.availableListOfLineNames.push(item);
}
});
});
};
Second Select Option in Form
<select name="lineName" ng-model="shift.lineName"
ng-options="x for x in availableListOfLineNames" id="selectoption2" required>
<option value="">Select One</option>
</select>
EDIT:
Calling $scope.selectLineNames(); inside $scope.editShift somehow makes the lineName value undefined after copy, on second time. Inside selectLineNames() too the value is available until it reaches the forEach() .Only after the loop starts It becomes undefined.
So used a duplicate method like $scope.selectLineNamesTemp(); and passed values from $scope.editShift and assigned them in the duplicate method like below.
$scope.selectLineNamesTemp = function(){
$scope.availableListOfLineNames = [];
$scope.availableListOfLineNamesTemp = LineDetails.ld_get_ln_resource.query(
{plant: plantTemp}, function(response) {
angular.forEach(response, function(item) {
if (item) {
$scope.availableListOfLineNames.push(item);
$scope.shift.lineName = lnTemp; // assigned from editShift
}
});
}) ;
};
Can someone point out why the value become undefined? Also is there a way to use the same old method without using the duplicate method. Hope someone help.