Add field with value to existing document in MongoDB via Java API

Question

The following code haven't worked for me:

public void addFieldWithValueToDoc(String DBName, String collName, String docID, String key, String value) {
    BasicDBObject setNewFieldQuery = new BasicDBObject().append("$set", new BasicDBObject().append(key, value));
    mongoClient.getDB(DBName).getCollection(collName).update(new BasicDBObject().append("_id", docID), setNewFieldQuery);
}

Where mongoClient variable's type is MongoClient.

It's inspired by Add new field to a collection in MongoDB . What's wrong and how to do it right? Thanks.

Your code should work. One thing can be the `_id` field. Is it really `String` or `ObjectId`? If the later is true, change your code to `append("_id", new ObjectId(docID))` — Ori Dar, Jan 08 '14 at 08:17
@orid is almost certainly correct - String docID will not match ObjectId() type. — Asya Kamsky, Jan 08 '14 at 09:23
In what way hasn't it worked? Was there an error, or did you not get the result you expected? Also, you don't need to do `new BasicDBObject().append(key, value)` you can simply do `new BasicDBObject(key, value)` — Trisha, Jan 08 '14 at 13:34

score 9 · Accepted Answer · answered Jan 08 '14 at 13:49

I've written a JUnit test to prove that your code does work:

@Test
public void shouldUpdateAnExistingDocumentWithANewKeyAndValue() {
    // Given
    String docID = "someId";
    collection.save(new BasicDBObject("_id", docID));
    assertThat(collection.find().count(), is(1));

    // When
    String key = "newKeyName";
    String value = "newKeyValue";
    addFieldWithValueToDoc(db.getName(), collection.getName(), docID, key, value);

    // Then
    assertThat(collection.findOne().get(key).toString(), is(value));
}

public void addFieldWithValueToDoc(String DBName, String collName, String docID, String key, String value) {
    BasicDBObject setNewFieldQuery = new BasicDBObject().append("$set", new BasicDBObject().append(key, value));
    mongoClient.getDB(DBName).getCollection(collName).update(new BasicDBObject().append("_id", docID), setNewFieldQuery);
}

So your code is correct, although I'd like to point out some comments on style that would make it more readable:

Parameters and variables should start with a lower-case letter. DBName should be dbName,
You don't need new BasicDBObject().append(key, value) use new BasicDBObject(key, value)

This code does the same thing as your code, but is shorter and simpler:

public void addFieldWithValueToDoc(String dbName, String collName, String docID, String key, String value) {
    mongoClient.getDB(dbName).getCollection(collName).update(new BasicDBObject("_id", docID),
                                                             new BasicDBObject("$set", new BasicDBObject(key, value)));
}

invzbl3 · Answer 2 · 2019-04-17T11:08:46.753

To update existing documents in a collection, you can use the collection’s updateOne() or updateMany methods.

updateOne method has the following form:

db.collection.updateOne(filter, update, options)

filter - the selection criteria for the update. The same query selectors as in the find() method are available.

Specify an empty document { } to update the first document returned in the collection.

update - the modifications to apply.

So, if you want to add one more field using Mongodb Java driver 3.4+, it will be:

collection.updateOne(new Document("flag", true),
                        new Document("$set", new Document("title", "Portable Space Ball")));

The following operation updates a single document where flag:true

Or in the same logic:

collection.updateOne(eq("flag", true),
                            new Document("$set", new Document("title", "Portable Space Ball")));

If the title field does not exist, $set will add a new field with the specified value, provided that the new field does not violate a type constraint. If you specify a dotted path for a non-existent field, $set will create the embedded documents as needed to fulfill the dotted path to the field.

Add field with value to existing document in MongoDB via Java API

2 Answers2