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· 2 min read
Bowei Xiao

There are two key components to make MongoDB accessible and serve as a server.

  1. MongoClient provided by the mongodb libs from MongoDB provider.
  2. Expressjs as the server hosting.

Here is the basic workflow diagram of MongoDB access

connection diagram

Database connection​

MongoClient:​

MongoClient.connect(mongoUri, {useNewUrlParser: true, useUnifiedTopology: true})
    .catch(err => {
        console.log(err);
        process.exit(1);
    })
    .then(async db => {
        await GedsyriaDb.DbAccess(db);
        app.listen(serverPort, () => {console.log(`listen on port ${serverPort}`)})

    });

DBAccess:​

After the connection succeeds, passing the DB entity into DBAccess to find the suitable collection in the cluster:

    static async DbAccess(conn) {
        if (geoSyria) {
            return
        }
        try {
            geoSyria = conn.db(db).collection(collection);
        } catch (e) {
            console.error('Uable connect to Database...' + e.message);
        }

    }

Server host​

Now using expressjs to host the server; from the design, we are querying 3 types of data:

  1. general data - the Latitude and Longitude data strings help the frontend locate the right spot on the 3D globe.
  2. yearly data - the death counts and sorted list (sorting list from server side)
  3. detail data - the details information of the selected string (through id)
...

const app = express();

...

const apiQuery = new express.Router();

apiQuery.route('/').get(apiController.responseData);
apiQuery.route('/year').get(apiController.responseSumData);
apiQuery.route('/id').get(apiController.responseDetailData);

app.use('/api', apiQuery);

module.exports = app;

The typical middleware response function has three input/output pipe: request, response, next, if the request.query has an id or year parameter, the response would trigger the conditional query to the database to get limited results.

static async responseSumData(req, res, next) {
    console.log("responseSum_query: " + req.query)
    try {
        let response = await DbAccess.getSumData(req.query);
        if (!response) {
            res.status(404).json({api_error: 'Not found'});
            return
        }
        return res.json(response);
    } catch (e) {
        console.error(`api server: ${e}`)
    }
}

As the response conducts the MongoDB query language 

arrayPipeline = [
    {
        $project: {
            year: 1,
            latitude: 1,
            longitude: 1,
            deaths_num: '$high'
        }
        }, {$sort: {deaths_num: -1}}, {$skip: 6}];
return await geoSyria.aggregate(arrayPipeline).toArray();

As a result, the front end will only get the specific data string relevant to the visualization's needs. And lots of calculations will be handled in the database directly, accelerating the interactive experiences.