AngularJS $q.defer defer object instance

1 Introduction

var deferred = $q.defer();// Deferred execution is declared, indicating that it is necessary to monitor subsequent executions

deferred.resolve(data); // The statement is executed successfully, that is, the http request data is successful, and the data can be returned

deferred.reject(data); // The statement failed to execute, that is, the server returned an error

return deferred.promise; // Return the promise, this is not the final data, but the API to access the final data

2. Method definition

var getList = function () {
    var result = [];
    var allData = [];
    var parentData = [];

    var deferred = $q.defer();

    var db = window.sqlitePlugin.openDatabase({ name: 'xunhu.db', location: 'default' });
    db.transaction(function (tx) {
        tx.executeSql('SELECT * FROM ShoppingCart', [], function (tx, rs) {
            for (var i = 0; i < rs.rows.length; i++) {
                allData.push(rs.rows.item(i));
            }
            //alert(allData.length);
        });
        tx.executeSql('SELECT DISTINCT(VendorId),VendorName FROM ShoppingCart', [], function (tx, rs) {
            for (var j = 0; j < rs.rows.length; j++) {
                parentData.push(rs.rows.item(j));
            }
            //alert(parentData.length);
        });
    }, function (error) {
        deferred.reject(error);
        console.log('transaction error: ' + error.message);
    }, function () {
        var jsonData = _.map(parentData, function (obj) {
            var child = _.filter(allData, function (o) {
                o.checked = false;
                return o.VendorId == obj.VendorId;
            })
            obj.childList = child;
            return obj;
            //delete obj.child
        });
        deferred.resolve(jsonData);
    });
    return deferred.promise;
}

3. Call

$scope.$on("$ionicView.beforeEnter", function () {
    getList().then(function (response) {
        $rootScope.shoppingCartList = response;
    }, function (error) {
        alert(123);
    });
});