How to get the size of single document in Mongodb?

Question

I encountered a strange behavior of mongo and I would like to clarify it a bit... My request is simple as that: I would like to get a size of single document in collection. I found two possible solutions: - Object.bsonsize - some javascript method that should return a size in bytes - db.collection.stats() - where there is a line 'avgObjSize' that produce some "aggregated"(average) size view on the data. It simply represents average size of single document. When I create test collection with only one document, both functions returns different values. How is it possible? Does it exist some other method to get a size of a mongo document? Here, I provide some code I perform testing on: I created new database 'test' and input simple document with only one attribute: type:"auto" ``` db.test.insert({type:"auto"}) ``` output from stats() function call: db.test.stats(): ``` { "ns" : "test.test", "count" : 1, "size" : 40, "avgObjSize" : 40, "storageSize" : 4096, "numExtents" : 1, "nindexes" : 1…

Accepted Answer

In the previous call of `Object.bsonsize()`, Mongodb returned the size of the cursor, rather than the document.

Correct way is to use this command:

```
Object.bsonsize(db.test.findOne())
```

With `findOne()`, you can define your query for a specific document:

```
Object.bsonsize(db.test.findOne({type:"auto"}))
```

This will return the correct size (in bytes) of the particular document.

How to get the size of single document in Mongodb?

Solution

Problem