filter Loopback API to get only rows with latest version

Question

I'm new to loopback so here is my question:

i have a model called "config-tables" with the following test data:

 [
    {
    ID: 0,
    CONFIG_NAME: "MainColor",
    DATA_TYPE: "color",
    CONFIG_VALUE: "#FF0000",
    VERSION: 1
    },

    {
    ID: 1,
    CONFIG_NAME: "MainColor",
    DATA_TYPE: "color",
    CONFIG_VALUE: "#FF00FF",
    VERSION: 2
    }
 ]

I want to create two custom methods and expose them to the API:

the first, a method to get the latest version.

the second, a method to get all data of the latest version, version=2 in this case.

i've read a lot about loopback filters but cannot figure how to use something similar to MAX or TOP in SQL.

Answer 1

Maybe there's something better to do - but I would simply create two remote methods in /common/models/config-tables.js in order to get the last element of your config-table entity ordered by VERSION attribute:

'use strict';
module.exports = function (configTable) {

    //first
    configTable.getLastVersion = function (cb) {
        // find only one configTable ordered by version
        configTable.findOne({order: 'VERSION DESC'}, function (err, config) {
            if(config && config.VERSION) {
                cb(err, config.VERSION);
            } else {
                // or throw a new error, depending on what you want
                cb(err, 0);
            }
        });
    };

    configTable.remoteMethod('getLastVersion', {
        returns: {arg: 'VERSION', type: 'number'},
        http: {verb: 'get'}
    });

    //second (depending on the first method)
    configTable.getLatests = function (cb) {
        configTable.getLastVersion(function (err, last_version) {
            if(err || !last_version || last_version === 0) {
                // maybe throw error here
                return cb(new Error("No config found actually..."));
            } else {
                // find all configTables where VERSION = last version
                configTable.find({where: {VERSION: last_version}}, function (err, configs) {
                    cb(err, configs);
                });
            }
        });
    };

    configTable.remoteMethod('getLatests', {
        returns: {arg: 'configTables', type: 'object'},
        http: {verb: 'get'}
    });
};