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The Ferreandina backend reads all runtime configuration from a .env file using the dotenv-java library. The .env file is loaded inside Connection.java the moment any controller opens its first MongoDB collection — no system-level environment variables or JVM flags are needed.

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Environment Variables

Both variables are required. The application will throw an exception at startup if either is missing from the .env file.
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MONGODB_URI
string
required
The full MongoDB connection string. Use mongodb://localhost:27017 for a local instance or a mongodb+srv://... URI for MongoDB Atlas.
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MONGODB_DB_NAME
string
required
The name of the MongoDB database to connect to, e.g. ferreandina. The database will be created automatically by MongoDB if it does not already exist.

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.env file example

Place this file in app/bc/ (the same directory where you run ./gradlew run): 
MONGODB_URI=mongodb://localhost:27017
MONGODB_DB_NAME=ferreandina

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MongoDB Connection

Connection<T extends Model> is a generic class that encapsulates the full lifecycle of a MongoDB connection for a single collection. When constructed it:
  1. Loads .env via Dotenv.load() and reads MONGODB_URI and MONGODB_DB_NAME.
  2. Calls createProviders() to build a POJO-aware CodecRegistry.
  3. Calls initMongo() to create the MongoClient and obtain a MongoDatabase reference with the custom codec applied.
Controllers call setCollection(name) to bind the connection to a specific MongoDB collection, storing it in the public collection field for direct use by the service layer. 
package com.ferreandina.database;

import org.bson.codecs.configuration.CodecProvider;
import org.bson.codecs.configuration.CodecRegistry;
import org.bson.codecs.pojo.PojoCodecProvider;
import static org.bson.codecs.configuration.CodecRegistries.fromProviders;
import static org.bson.codecs.configuration.CodecRegistries.fromRegistries;

import com.ferreandina.models.Model;
import com.mongodb.MongoClientSettings;
import com.mongodb.client.MongoClient;
import com.mongodb.client.MongoClients;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;

import io.github.cdimascio.dotenv.Dotenv;

public class Connection<T extends Model> {
    private String uri;
    private String dbName;
    private CodecRegistry customCodec;
    private Class<T> model;
    public MongoClient client;
    public MongoDatabase db;
    public MongoCollection<T> collection;

    public Connection(Class<T> clazz) {
        this.model = clazz;
        Dotenv env = Dotenv.load();
        this.uri = env.get("MONGODB_URI");
        this.dbName = env.get("MONGODB_DB_NAME");

        System.out.println(uri);
        System.out.println(dbName);
        this.createProviders();
        this.initMongo();
    }

    private final void createProviders() {
        CodecProvider customClassBuilder = PojoCodecProvider.builder().automatic(true).build();
        this.customCodec = fromRegistries(
                MongoClientSettings.getDefaultCodecRegistry(),
                fromProviders(customClassBuilder));
    }

    private final void initMongo() {
        this.client = MongoClients.create(uri);
        this.db = this.client.getDatabase(this.dbName).withCodecRegistry(this.customCodec);
    }

    public final MongoCollection<T> getCollection(String name) {
        return this.db.getCollection(name, this.model);
    }

    public final void setCollection(String name) {
        this.collection = this.getCollection(name);
    }

    public final void printCollection(String name) {
        for (T m : this.collection.find()) {
            System.out.println(m.toString());
        }
    }
}

​
POJO Codec Configuration

The createProviders() method registers a PojoCodecProvider built with .automatic(true). This instructs the MongoDB driver to automatically map BSON documents to and from any Java POJO it encounters — no manual field mapping or custom codecs are required for model classes. 
private final void createProviders() {
    CodecProvider customClassBuilder = PojoCodecProvider.builder().automatic(true).build();
    this.customCodec = fromRegistries(
            MongoClientSettings.getDefaultCodecRegistry(),
            fromProviders(customClassBuilder));
}
The resulting CodecRegistry is composed from two layers:
  1. MongoClientSettings.getDefaultCodecRegistry() — handles all primitive types, ObjectId, BsonValue, Date, etc.
  2. fromProviders(customClassBuilder) — handles automatic POJO serialization for model classes (e.g., BranchModel, ProductModel).
The combined registry is applied to the MongoDatabase instance via withCodecRegistry(this.customCodec), so every collection opened from that database inherits POJO support automatically.

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CORS

App.java enables CORS globally using Javalin’s bundled plugin, configured with anyHost(): 
config.bundledPlugins.enableCors(cors -> {
    cors.addRule(it -> {
        it.anyHost();
    });
});
This allows any origin to call the API, which is convenient during local development when the frontend and backend run on different ports.
anyHost() permits cross-origin requests from every domain. Before deploying to a production or staging environment, replace it with an explicit allowed-origins list to prevent unauthorized browsers from calling your API.
cors.addRule(it -> {
    it.allowHost("https://your-frontend-domain.com");
});

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MongoDB Atlas

To connect to a cloud-hosted Atlas cluster, replace MONGODB_URI with the Atlas connection string found in the Connect dialog of your cluster. No code changes are needed — Connection.java uses the URI as-is. 
MONGODB_URI=mongodb+srv://<username>:<password>@cluster0.example.mongodb.net
MONGODB_DB_NAME=ferreandina
Make sure your Atlas cluster’s Network Access list includes the IP address of the machine running the backend, or set it to 0.0.0.0/0 for unrestricted access during development.

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