How do I check whether a field contains null value? - pymongo

Question

Sometimes my document has a field that has null values. - How do I check whether the value inside a field is a null string? - How do I iterate through all documents and delete the field of the document if it has a null string value? - Should I delete this field for this document, so that i can do this to find the empty field? `for i in v7.find({"eng":{"$exist":True}})` An example of my document structure is as such: ``` { "_id" : ObjectId("50fd55c1161747668078fed6"), "dan" : "Hr. Hänsch repræsenterede Dem dér .", "deu" : "Der Kollege Hänsch hat Sie dort vertreten .", "eng" : "Mr Hänsch represented you on this occasion .", "fin" : "Kollega Hänsch edusti teitä siellä .", "ita" : "Il collega Hänsch è intervenuto in sua vece .", "md5" : "336b9cd1dc01ae0ff3344072d8db0295", "uid" : 2100986 } {u'uid': 104, u'fre': u"Je crois que la pr\xe9vention est d' une importance capitale , et ce non pas \xe0 cause des criminels \xe0 la t\xeate du pouvoir .", u'eng': u'', u'dan': u'Som hr .', u'deu': u'.…

Accepted Answer

According to manuals of mongodb the following query achieve this:

```
db.test.find( { eng : { $type: 10 } } )
```

The query returns only the document that contains the null value:

The { field : { $type: 10 } } query matches documents that contains the field whose value is null only; i.e. the value of the field is of BSON Type Null (i.e. 10)

http://docs.mongodb.org/manual/faq/developers/#faq-developers-query-for-nulls

How do I check whether a field contains null value? - pymongo

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