There could be several reasons why an object value is not updating in MongoDB. Here are some common ones and how to debug the problem:
1. Syntax error update operation
The update operation has been written incorrectly, thus failing to perform an update. Double-check you are using the correct update operator of MongoDB.
Common mistake: Absence of $set operator.
Correct application: When updating a value within an object, it must be done with $set to tell mongo explicitly that it is an update of that field.
Example:
db.collection.updateOne(
{ _id: ObjectId("some_id") },
{ $set: { "objectField.subField": "newValue" } }
);
Otherwise, we could just replace the document or leave it unchanged, depending on the operation performed by MongoDB.
2. Wrong Object Field Path
If the path for the object or field is incorrect, the update will not be applied to the subfield in a manner that it was supposed to be. So make sure the field name and path pointing to it are correct.
Example: If you want to update a field inside a nested object, the path should be specified with dot notation:
db.collection.updateOne(
{ _id: ObjectId("some_id") },
{ $set: { "profile.address.city": "New York" } }
);
Here, profile.address.city must exist in the document or else the update won't work.
3. No Document or Condition Failed
In situations where the updated operation does not match documents, given the filter, then no update occurs.
Debugging:
Check if your filter condition is accurate.
Use updateOne() for single document filtering and make use of updateMany() for multiple documents with a matching filter.
For example:
db.collection.updateOne(
{ _id: ObjectId("some_id") },
{ $set: { "objectField.subField": "newValue" } }
);
An existing document with the specified _id will not produce any outcome from the update.
