My MongoDB .find() method is returning null even thought the data exists-CodePudding

I am trying to find a user's UUID in my database, but it's returning null for no reason. It's in the connect() method. I can find this manually, and in my project in javaScript. But for some reason, I'm getting this error.

public final class DiscordLink extends JavaPlugin implements Listener {
public MongoCollection<Document> users;
public MongoDatabase mongoDatabase;
    @Override
    public void onEnable() {
        System.setProperty("DEBUG.GO", "true");
        System.setProperty("DB.TRACE", "true");
        Logger mongoLogger = Logger.getLogger("org.mongodb.driver");
        mongoLogger.setLevel(Level.WARNING);
        connect();

        getServer().getConsoleSender().sendMessage(ChatColor.GREEN   "[DiscordLink] Plugin enabled...");

        getServer().getPluginManager().registerEvents(this, this);

    }

    @Override
    public void onDisable() {
        getServer().getConsoleSender().sendMessage(ChatColor.RED   "[DiscordLink] Plugin disabled...");
    }

    public void connect() {
        MongoClient mongoClient = MongoClients.create("MONGOURI");
        MongoDatabase mongoDatabase = mongoClient.getDatabase("myFirstDatabase");
        MongoCollection<Document> users = mongoDatabase.getCollection("users");
        Bukkit.getConsoleSender().sendMessage(ChatColor.GREEN   "[DiscordLink] Connected to database!");
    }

    @EventHandler
    public void onPlayerJoin(PlayerJoinEvent event) {
        Player player = event.getPlayer();
        Document document = users.find(Filters.eq("mcUUID", player.getUniqueId().toString())).first();
        if(document != null) {
            player.kickPlayer(ChatColor.RED   "Discord Authentication Failed!");
        } else { return; }

Error:

[15:43:01 ERROR]: Could not pass event PlayerJoinEvent to DiscordLink v1.0-SNAPSHOT
java.lang.NullPointerException: Cannot invoke "com.mongodb.client.MongoCollection.find(org.bson.conversions.Bson)" because "this.users" is null

CodePudding user response：

In the connect method, you are declaring the field MongoCollection<Document> users.

If you IDE is well configurated, it should tell you that this field is not used. Here, you are creating a local field (that keep only in the method scope) instead of setting the global field, which is declared just below the public final class DiscordLink.

To fix it, do like this :

this.mongoDatabase = mongoClient.getDatabase("myFirstDatabase")
this.users = this.mongoDatabase.getCollection("users");

Here, the this key-word is to say you are looking for the global variable, declared outside of the method.