MongoDB Installation

const { MongoClient } = require('mongodb');

class WorldDatabase {
    constructor(connectionString = 'mongodb://localhost:27017') {
        this.connectionString = connectionString;
        this.client = null;
        this.db = null;
    }
    
    async connect() {
        this.client = new MongoClient(this.connectionString);
        await this.client.connect();
        this.db = this.client.db('world');
    }
    
    async getCountries(region = null, limit = null) {
        const query = region ? { region } : {};
        let cursor = this.db.collection('countries').find(query);
        if (limit) cursor = cursor.limit(limit);
        return await cursor.toArray();
    }
    
    async getCitiesByCountry(countryCode, limit = null) {
        const query = { country_code: countryCode };
        let cursor = this.db.collection('cities').find(query);
        if (limit) cursor = cursor.limit(limit);
        return await cursor.toArray();
    }
    
    async searchCities(searchTerm, limit = 10) {
        return await this.db.collection('cities')
            .find(
                { $text: { $search: searchTerm } },
                { projection: { score: { $meta: 'textScore' } } }
            )
            .sort({ score: { $meta: 'textScore' } })
            .limit(limit)
            .toArray();
    }
    
    async findNearbyCities(longitude, latitude, maxDistance = 100000) {
        return await this.db.collection('cities').find({
            location: {
                $near: {
                    $geometry: {
                        type: "Point",
                        coordinates: [longitude, latitude]
                    },
                    $maxDistance: maxDistance
                }
            }
        }).toArray();
    }
    
    async getCountryStatistics() {
        const pipeline = [
            {
                $group: {
                    _id: "$region",
                    countries: { $sum: 1 },
                    currencies: { $addToSet: "$currency" }
                }
            },
            { $sort: { countries: -1 } }
        ];
        
        return await this.db.collection('countries').aggregate(pipeline).toArray();
    }
    
    async close() {
        if (this.client) {
            await this.client.close();
        }
    }
}

// Usage example
async function example() {
    const db = new WorldDatabase();
    
    try {
        await db.connect();
        
        // Get European countries
        const europeCountries = await db.getCountries('Europe', 5);
        console.log('European Countries:');
        europeCountries.forEach(country => {
            console.log(`  ${country.name} (${country.iso2})`);
        });
        
        // Get US cities
        const usCities = await db.getCitiesByCountry('US', 5);
        console.log('\nUS Cities:');
        usCities.forEach(city => {
            console.log(`  ${city.name}, ${city.state_name}`);
        });
        
        // Search cities
        const searchResults = await db.searchCities('paris', 5);
        console.log('\nCities matching "paris":');
        searchResults.forEach(city => {
            console.log(`  ${city.name}, ${city.country_name}`);
        });
        
        // Country statistics
        const stats = await db.getCountryStatistics();
        console.log('\nCountries by region:');
        stats.forEach(stat => {
            console.log(`  ${stat._id}: ${stat.countries} countries`);
        });
        
    } catch (error) {
        console.error('Database error:', error);
    } finally {
        await db.close();
    }
}

example();

import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.data.mongodb.core.query.Criteria;
import org.springframework.data.mongodb.core.query.Query;
import org.springframework.data.mongodb.core.query.TextCriteria;
import org.springframework.data.mongodb.core.query.TextQuery;
import org.springframework.data.geo.Distance;
import org.springframework.data.geo.Metrics;
import org.springframework.data.geo.Point;
import org.springframework.data.mongodb.core.query.NearQuery;

import java.util.List;

public class WorldDatabase {
    
    private final MongoTemplate mongoTemplate;
    
    public WorldDatabase(MongoTemplate mongoTemplate) {
        this.mongoTemplate = mongoTemplate;
    }
    
    public List<Country> getCountries(String region, Integer limit) {
        Query query = new Query();
        if (region != null) {
            query.addCriteria(Criteria.where("region").is(region));
        }
        if (limit != null) {
            query.limit(limit);
        }
        return mongoTemplate.find(query, Country.class, "countries");
    }
    
    public List<City> getCitiesByCountry(String countryCode, Integer limit) {
        Query query = new Query(Criteria.where("country_code").is(countryCode));
        if (limit != null) {
            query.limit(limit);
        }
        return mongoTemplate.find(query, City.class, "cities");
    }
    
    public List<City> searchCities(String searchTerm, int limit) {
        TextCriteria criteria = TextCriteria.forDefaultLanguage().matchingAny(searchTerm);
        Query query = TextQuery.queryText(criteria).sortByScore().limit(limit);
        return mongoTemplate.find(query, City.class, "cities");
    }
    
    public List<City> findNearbyCities(double longitude, double latitude, double maxDistanceKm) {
        Point location = new Point(longitude, latitude);
        Distance distance = new Distance(maxDistanceKm, Metrics.KILOMETERS);
        Query query = new Query(Criteria.where("location").near(location).maxDistance(distance.getNormalizedValue()));
        return mongoTemplate.find(query, City.class, "cities");
    }
}

// Entity classes
@Document(collection = "countries")
public class Country {
    @Id
    private String id;
    private String name;
    private String iso2;
    private String iso3;
    private String region;
    private String subregion;
    private String capital;
    private String currency;
    private String phone_code;
    
    // Getters and setters...
}

@Document(collection = "cities") 
public class City {
    @Id
    private String id;
    private String name;
    private String state_name;
    private String country_name;
    private String country_code;
    private String state_code;
    private String latitude;
    private String longitude;
    
    // Getters and setters...
}