集合的返回类型。使用 java 在 mongodb 中查找

Question

I am trying to implement a simple login function using java where a user enters a username and password through a text field and then these credentials are checked against a set of documents in a collection in mongodb, using maven dependencies. The connection with the database has been made and relevant imports added.

import com.mongodb.client.FindIterable;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import org.bson.Document;
import static com.mongodb.client.model.Filters.and;
import static com.mongodb.client.model.Filters.eq;

String user  = txtUser.getText();
String pass = txtPass.getText();

MongoDatabase db = DbConnection.getDbConnection();
MongoCollection collection = db.getCollection("Admin");
FindIterable<Document> findLogin = collection.find(and(eq("username", user),eq("password",pass)));

if(findLogin == null){
     System.out.println("Failed");
}else{
      System.out.println("Successful");
}

The problem here is that successful is displayed even when the wrong credentials are entered. This is my first time using mongodb so I am not entirely sure of the queries that can be run on mongodb. What type of value does the collection.find return. And what are the possible methods I could follow to overcome the problem?

Answer 1

The FindIterable returned by the find() method of MongoCollection will not be null . In order to determine whether any documents were matched by your query, you need to inspect the FindIterable .

In your case, the first() method is the most appropriate. This way you get a single document to perform a null check on. Put all together it may look like this:

Document loginDoc = collection.find(and(eq("username", user),eq("password",pass))).first();

if (loginDoc == null) {
     System.out.println("Failed");
} else {
     System.out.println("Successful");
}