在获取对象的同时获得sum sum字段

Question

我有一张看起来像这样的表

var competence_develop_comp = sequelize.define('competence_develop_comp', {
            competence_id: {
                type: DataTypes.INTEGER,
                primaryKey: true
            },
            level_difference: DataTypes.INTEGER,
            division_id: DataTypes.INTEGER,
            timestamp : DataTypes.DATE
        }, {
            freezeTableName: true,
            instanceMethods: {
                retrieveByDivision: function (adminDivisions, onSuccess, onError) {
                    competence_develop_comp.sum('level_difference',{
                        include: [{model: Competence}],
                        where: {division_id: {$in: adminDivisions}},
                        order: 'timestamp DESC,level_difference DESC',
                        GROUP: 'competence_id',
                        limit: 10
                    }).ok(onSuccess).error(onError);
                },
                retrieveByDivisionId: function (division_id, onSuccess, onError) {
                    competence_develop_comp.findAll({
                        include: [{model: Competence}],
                        where: {division_id: division_id},
                        order: 'timestamp DESC,     level_difference DESC',
                        limit: 10
                    }).ok(onSuccess).error(onError);
                }
            }
        }
    );

正如您所见，我已尝试使用以下内容sum字段level_difference：

competence_develop_comp.sum('level_difference',{
                        include: [{model: Competence}],
                        where: {division_id: {$in: adminDivisions}},
                        order: 'timestamp DESC,level_difference DESC',
                        GROUP: 'competence_id',
                        limit: 10
                    }).ok(onSuccess).error(onError);

然而，当我这样做时，我收到以下错误：

TypeError: Cannot call method 'map' of undefined

对于每个结果，我需要level_difference

的总和

那么我将如何使用sequelize

执行此操作