this.listenModelChange = function (openid, nodeName, cb) {
    console.log('watch...'+JSON.stringify({openid,nodeName}))
    watchModel= db.collection('on_off_model_state').where({
        _openid: openid,
        nodeName: nodeName

    }).watch({
        onChange: function (snapshot) {
            if (cb)
                cb(snapshot)
        },
        onError: function (err) {
            console.error('the on_off_model_state watch closed because of error', err)
        }
    })
}

this.listenGroupChange = function (openid, cb) {
    console.log('watch openid:'+openid)
    groupWacth= db.collection('groups').where({
        _openid: openid
    }).watch({
        onChange: function (snapshot) {
            if (cb)
                cb(snapshot)
        },
        onError: function (err) {
            console.error('the groups watch closed because of error', err)
        }
    })
}
this.listenNodeChange = function (openid, cb) {
    nodesWatch= db.collection('provisioned_nodes').where({
        _openid: openid
    }).watch({
        onChange: function (snapshot) {
            if (cb)
                cb(snapshot)
        },
        onError: function (err) {
            console.error('the watch closed because of error', err)
        }
    })
}