Bridging the gap between Sails.js and ng-admin

Sails.js is an MVC Framework for node.js with many features directly out of the box that make prototyping web applications a lot faster and easier. One of these features is called Blueprints and automatically generates a REST API based on your Model definition.

ng-admin is an Angular.js Application that can be connected to any REST API and, with some configuration, presents a fully-featured CRUD interface for all entities accessible through the API.

Bringing the two together allows us to add an admin interface to an API with minimal programming effort. However, the two don’t work together perfectly out of the box. Most features already work, but to get everything up and running properly, especially list views with pagination, some minor changes must be made in both projects.

Sorting and Limiting for List Views

ng-admin adds some parameters to its GET Requests that are supposed to tell Sails.js how many objects to return and how many to skip. However, Sails.js does not understand these parameters and therefore list views do not work initially. But, as described in the chapter “Customizing the API Mapping” in the ng-admin documentation, it is possible to change the way it builds up its request.

This can be done in the ng-admin.js file, where we set up your ng-admin application anyway. For Sails.js, the following code needs to be added after the call to admin.config:

admin.config(['RestangularProvider', function(RestangularProvider) {
    RestangularProvider.addFullRequestInterceptor(function(element, operation, what, url, headers, params, httpConfig) {
        if (operation == 'getList') {
            params.skip = (params._page - 1) * params._perPage;
            params.limit = params._perPage;
            params.sort = params._sortField + ' ' + params._sortDir;
            delete params._sortField;
            delete params._sortDir;
            delete params._page;
            delete params._perPage;
        }
        return { params: params };
    });
}]);

How this modifies the parameters is pretty obvious, but how when or why this is called not so much. It seems to be working with Angular.js dependency injection, but so far I haven’t worked enough with Angular.js to be sure.

Pagination in List Views

So far, ng-admin will only display a single page of results inside every list view. That happens because it has no idea how many items actually exist behind the API. It wants to read this information from a special HTTP-Header called X-Total-Count. Sails.js does not set this header, so pagination does not work.

Now, we could go and add logic to every Controller to count the total number of objects in our database and set the X-Total-Count Header. While it would work, it would be kind of dumb, because we would have to copy and maintain the same code in each and every controller that is part of our API.

Fortunately, Sails.js allows us to override parts of blueprints with custom logic. We need to override the find action with a version that counts the number of entries and sends it to ng-admin inside the X-Total-Count Header. To do so, we create a new directory inside our api directory, called blueprints. Inside this directory, we create a file called find.js with the following content:

'use strict';

/**
 * Adds the X-Total-Count Header to REST calls to support pagination in ng-admin
 */

/**
 * Module dependencies
 */
var actionUtil = require('sails/lib/hooks/blueprints/actionUtil');
var _ = require('lodash');
var async = require('sails/node_modules/async');

/**
 * Find Records
 *
 *  get   /:modelIdentity
 *   *    /:modelIdentity/find
 *
 * An API call to find and return model instances from the data adapter
 * using the specified criteria.  If an id was specified, just the instance
 * with that unique id will be returned.
 *
 * Optional:
 * @param {Object} where       - the find criteria (passed directly to the ORM)
 * @param {Integer} limit      - the maximum number of records to send back (useful for pagination)
 * @param {Integer} skip       - the number of records to skip (useful for pagination)
 * @param {String} sort        - the order of returned records, e.g. `name ASC` or `age DESC`
 * @param {String} callback - default jsonp callback param (i.e. the name of the js function returned)
 */

module.exports = function findRecords(req, res) {

    // Look up the model
    var Model = actionUtil.parseModel(req);

    // Lookup for records that match the specified criteria
    var queryData = Model.find()
        .where( actionUtil.parseCriteria(req) )
        .limit( actionUtil.parseLimit(req) )
        .skip( actionUtil.parseSkip(req) )
        .sort( actionUtil.parseSort(req) );
    queryData = actionUtil.populateRequest(queryData, req);

    var queryCount = Model.count().where(actionUtil.parseCriteria(req));

    // Expose header to the client
    res.set('Access-Control-Expose-Headers', 'X-Total-Count');

    async.parallel(
        { data: getData, count: getTotalCount },
        function (err, results) {
            res.set('X-Total-Count', results.count);
            res.ok(results.data);
        }
    );

    function getTotalCount(cb) {
        queryCount.exec(function (err, count) {
            cb(null, count);
        });
    }

    function getData(cb) {
        queryData.exec(function found(err, matchingRecords) {
            if (err) return res.serverError(err);
            // Only `.watch()` for new instances of the model if
            // `autoWatch` is enabled.
            if (req._sails.hooks.pubsub && req.isSocket) {
                Model.subscribe(req, matchingRecords);
                if (req.options.autoWatch) { Model.watch(req); }
                // Also subscribe to instances of all associated models
                _.each(matchingRecords, function (record) {
                    actionUtil.subscribeDeep(req, record);
                });
            }

            cb(null, matchingRecords);
        });
    }
};

This will now get called whenever ng-admin requests data for a list view and sends the proper header along with the data. The code is heavily based on the original implementation of find.js and some code I found in a Gist on Github. I only updated it a bit to work with a newer version of Sails.js (0.12 in this case).

Because the code above requires lodash and we cannot rely on lodash automatically shipping with Sails.js, we need to install it via npm before everything works:

npm require lodash --save

With these 2 changes in place, our ng-admin application should now be able to nicely display list views for our automatically generated Sails.js API.

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