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maksbd19/dumboDB-file-read-write.js

Created April 3, 2019 16:23
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  1. maksbd19 created this gist Apr 3, 2019.
    105 changes: 105 additions & 0 deletions dumboDB-file-read-write.js
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,105 @@
    const fs = require('fs');
    const path = require('path');

    const dbFilePath = path.join(__dirname, 'db.json'); // path to the json file where we are storing our hash data
    const MAX_TRY_COUNT = 5; // Maximum numebr of attempts in case of failure

    let readTryCount = 0; // hold the read try count
    let writeTryCount = 0; // hold the write try count

    const hash = {};

    // to get the value for a particular index
    const get = index => typeof hash[index] !== "undefined" ? hash[index] : null;

    // add a new value in a particular index
    const set = (index, data) => {
    if( typeof hash[index] === "undefined"){
    hash[index] = [];
    }
    hash[index].push(data);
    }

    // remove a value from a particular index
    const pop = (index, value) => {
    if( typeof hash[index] === "undefined"){
    return true;
    }

    const valueIndex = hash[index].indexOf(value);
    if(valueIndex > -1){
    hash[index].splice(valueIndex, 1);
    }

    commitDB(); // updating the file with latest hash content

    return true;
    }

    // remove all values stored in a particular index
    const remove = index => {
    if( typeof hash[index] !== "undefined"){
    delete hash[index];
    }

    commitDB(); // updating the file with latest hash content

    return true;
    }

    const readDB = () => {
    fs.readFile(dbFilePath, (err, data) => {
    if(err){
    if(readTryCount < MAX_TRY_COUNT){
    setTimeout(readDB, 1000); // let's try again 1s later
    }
    else{
    throw err; // raise the error
    }
    }
    try{
    data = JSON.parse(data);
    // hash is a constant so we can't directly assign the data
    // we can assign properties by the way
    for (key in data) {
    hash[key] = data[key]; // copies each property to the data object
    }
    readTryCount = 0;
    }
    catch(e){
    throw e; // bad data?
    }

    });
    }

    // commiting the changes in the file
    const commitDB = () => {
    const data = JSON.stringify(hash);
    const options = {
    encoding: 'utf8'
    };

    fs.writeFile(dbFilePath, data, options, (err) => {
    if(err){
    if(writeTryCount < MAX_TRY_COUNT){
    setTimeout(commitDB, 1000); // let's try again 1s later
    writeTryCount++;
    }
    else{
    throw err; // raise the error
    }
    }

    // file is updated so nothing to do here...
    writeTryCount = 0;
    });
    }

    // Read the file for the first time when the module loads
    readDB();

    // exposing the getter and setters
    exports.get = get;
    exports.pop = pop;
    exports.remove = remove;