Trying to update a document using MongoDB Java Driver

Question

Thank you

I just want to thank you for clicking on this question! I've tried my best to make this as thorough as possible.
but still, feel free to let me know if you need to clarify anything further!
if you think the question is too long. you can just read the third & fourth part and post your own solution down here!

Setup

Mongodb Java driver: org.mongodb:mongo-java-driver:3.11.0-rc0

What I want to do

find a specific document with a specific "name" field.
then update the other field or the whole document.

Example Document

// the document that I am trying to find in db
{
  "_id":"5de6af7cfa42833bd9849477",
  "name":"Richard Koba",
  "skills":[]
}

// the document that I have
{
  "name":"Richard Koba",
  "skills":[jump, dance, sing]
}

// final result in db
{
  "_id":"5de6af7cfa42833bd9849477",
  "name":"Richard Koba",
  "skills":[jump, dance, sing]
}

What I am doing now

  // finding a document with same "name" field as input doc and update it with doc
  public MongoCollection updateDocument(Document doc, String colName) {
    MongoCollection collection;

    // make sure collection exist
    try {
      collection = connectCollection(colName); // returns MongoCollection Obj
    } catch (CollectionNotFoundException e) {
      MessageHandler.errorMessage(e.getMessage());
      return null;
    }

    // trying to find the document.
    if (collection.find(eq("name", doc.get("name"))).first() == null) {
      // if document not found, insert a new one
      collection.insertOne(doc);
    } else {
      // if the document found, replace/update it with the one I have
      collection.replaceOne(eq("name", doc.get("name")), doc);
    }

    return collection;
  }

What I found about my false solution

collection.find(eq("name", doc.get("name"))).first() never returns null.
Java only tells me it returns an Object. MongoDB Documentation tells me it is a TResult, which point back to MongoIterable. I am stuck here.
the code outcome is that none of the documents is inserted/updated in the end.

Reference

https://mongodb.github.io/mongo-java-driver/3.11/javadoc/com/mongodb/client/MongoIterable.html#first()

prasad_ · Accepted Answer

I tried some code and this works fine. This is not much different from your code.

Created a document from mongo shell:

MongoDB Enterprise > db.users.findOne()
{
        "_id" : "5de6af7cfa42833bd9849477",
        "name" : "Richard Koba",
        "skills" : [ ]
}

My Java Code:

// Test input documents
private Document doc1 = new Document()
                           .append("name", "Richard Koba")
                           .append("skills", Arrays.asList("jump", "dance", "sing"));
private Document doc2 = new Document()
                            .append("name", "Richard K")
                            .append("skills", Arrays.asList("sings"));

When doc1 is passed to the following method the result is: "### Doc FOUND". And, with doc2 the result is "### Doc NOT found".

private void checkDocument(Document doc) {

    MongoClient mongoClient = MongoClients.create("mongodb://localhost/");
    MongoDatabase database = mongoClient.getDatabase("javadb");
    MongoCollection collection = database.getCollection("users");

    if (collection.find(eq("name", doc.get("name"))).first() == null) {

        System.out.println("### Doc NOT found");
    } 
    else {
        System.out.println("### Doc FOUND");
    }
}

I also tried this, with the same results.

Document d = collection.find(eq("name", doc.get("name"))).first();
if (d == null) { // ... }

I also tried this; works fine too.

if (collection.find(queryFilter).iterator().tryNext() == null) { // ... }

I think there might be some other issue with your code or the database / collection. Some debugging and testing with new data might reveal the real issue.

Did you check if the document already exists in the collection, from mongo shell or Compass tools?
Are you using the right database and collection names?
After each test run are you verifying the data in the database if it is updated / inserted?

collection.find(eq("name", doc.get("name"))).first() never returns null.

With the code I posted above, the find query did return null when the users collection was empty.