express-promise

An express.js middleware for easy rendering async query.

Cases

1. previously

app.get('/users/:userId', function(req, res) {
    User.find(req.params.userId).then(function(user) {
        Project.getMemo(req.params.userId).then(function(memo) {
            res.json({
                user: user,
                memo: memo
            });
        });
    });
});

1. now

app.get('/users/:userId', function(req, res) {
    res.json({
        user: User.find(req.params.userId),
        memo: Project.getMemo(req.params.userId)
    });
});

2. previously

app.get('/project/:projectId', function(req, res) {
    var field = req.query.fields.split(';');
    var result = {};

    var pending = 0;
    if (field.indexOf('people') !== -1) {
        pending++;
        Project.getField(req.params.projectId).then(function(result) {
            result.people = result;
            if (--pending) {
                output();
            }
        });
    }

    if (field.indexOf('tasks') !== -1) {
        pending++;
        Project.getTaskCount(req.params.projectId).then(function(result) {
            result.tasksCount= result;
            if (--pending) {
                output();
            }
        });
    }

    function output() {
        res.json(result);
    }
});

2. now

app.get('/project/:projectId', function(req, res) {
    var field = req.query.fields.split(';');
    var result = {};

    if (field.indexOf('people') !== -1) {
        result.people = Project.getField(req.params.projectId);
    }

    if (field.indexOf('tasks') !== -1) {
        result.tasksCount = Project.getTaskCount(req.params.projectId);
    }

    res.json(result);
});

Install

$ npm install express-promise

Usage

Just app.use it!

app.use(require('express-promise')());

This library supports the following methods: res.send, res.json, res.render.

If you want to let express-promise support nodejs-style callbacks, you can use dotQ to convert the nodejs-style callbacks to Promises. For example:

require('dotq');
app.use(require('express-promise')());

var fs = require('fs');
app.get('/file', function(req, res) {
    res.send(fs.readFile.promise(__dirname + '/package.json', 'utf-8'));
});

Skip traverse

As a gesture to performance, when traverse an object, we call toJSON on it to reduce the properties we need to traverse recursively. However that's measure has some negative effects. For instance, all the methods will be removed from the object so you can't use them in the template.

If you want to skip calling toJSON on an object(as well as stop traverse it recursively), you can use the skipTraverse option. If the function return true, express-promise will skip the object.

app.use(require('express-promise')({
  skipTraverse: function(object) {
    if (object.hasOwnProperty('method')) {
      return true;
    }
  }
}))

Libraries

express-promise works well with some ODM/ORM libraries such as Mongoose and Sequelize. There are some examples in the /examples folder.

Mongoose

When query a document without passing a callback function, Mongoose will return a Query instance. For example:

var Person = mongoose.model('Person', yourSchema);
var query = Person.findOne({ 'name.last': 'Ghost' }, 'name occupation');

Query has a exec method, when you call query.exec(function(err, result) {}), the query will execute and the result will return to the callback function. In some aspects, Query is like Promise, so express-promise supports Query as well. You can do this:

exports.index = function(req, res){
  res.render('index', {
    title: 'Express',
    cat: Cat.findOne({name: 'Zildjian'})
  });
};

and in the index.jade, you can use cat directly:

p The name of the cat is #{cat.name}

Sequelize

Sequelize supports Promise after version 1.7.0 :)

Articles and Recipes

• Node Roundup: Bedecked, Knockout.sync.js, express-promise
• 减少异步嵌套，Express-promise [Chinese]

License

The MIT License (MIT)

Copyright (c) 2013 Zihua Li

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.