pymongo-数组的mongo文档bson大小

Question

I'm trying to capture the array size(bson size in bytes) using pymongo. Below is the sample document structure,

I'm able to retrieve the entire document size using following code snippet,

for doc in src_db.src_coll.find({'customProperties':{ '$exists' : True }}).limit(2):
    print(len(bson.BSON.encode(doc)))

But I'm unable to calculate the size of each sub array, example code which is failing,

for doc in src_db.Quotes.find({'customProperties':{ '$exists' : True }}).limit(1):
    print('doc_size:'+str(len(bson.BSON.encode(doc))))
    doc_customProp =  doc["customProperties"]
    print('custom_prop_size:'+str(len(bson.BSON.encode(doc_customProp))))

Output with Error:

doc_size: 363953
Traceback (most recent call last):
  File "./document_stats.py", line 15, in <module>
    print('custom_prop_size:'+str(len(bson.BSON.encode(doc_customProp))))
  File "/usr/lib64/python2.7/site-packages/bson/__init__.py", line 976, in encode
    return cls(_dict_to_bson(document, check_keys, codec_options))
TypeError: encoder expected a mapping type but got: [[u'custValue', u'{"identifier":"","productId":["3"]}']]

Expected output:

doc_size: 363953
custom_prop_size: *****

Answer 1

You should be able to limit what you get back from MongoDB by using projection like this:

src_db.Quotes.find({'customProperties':{ '$exists' : True }}, {"_id": 0, "customProperties": 1})

Then you can simply get the size of the entire document.