How to write Mongoose Queries with optional express query-params?
<p>I am building a REST API on top of Express 4. For a path lets say <code>GET /api/users</code> I want to query my users collection accordingly to <strong><em>optional</em></strong>  queryParams.</p>

<p>So a call to the API could look like this <code>host:port/api/users?city=Berlin</code></p>

<p>In this case <code>name</code> is omitted and doesn't influence the query, whereas <code>city</code> has to match.</p>

<p>I managed to do this with the following hack. Is there a better way than that?</p>

<pre><code>Users.statics.customFilter = function(qP){
    return this.find({
        $and: [
            {$or: [{undefined: {$eq: qP.city}}, {'city': qP.city}]},
            {$or: [{undefined: {$eq: qP.name}}, {'name': qP.name}]}
        ]
    });

mongoose.model('User', Users);
</code></pre>

<p>I'm calling this static function from the mongoose schema like this...      </p>

<pre><code>const User = mongoose.model('User');
app.get('/api/users', (req, res) =&gt; {
        User.customFilter(req.query)
        .exec((err, results) =&gt; {
            if (err) return next(err);
            res.json(results);
        });
    });
</code></pre>