CODEWITHSUNDEEP
mongodbpymongo
David Dehghan
David Dehghan

Reputation: 24845

Test empty string in mongodb and pymongo

Here is my data structure. 

[{
"name": "David",
"lastname": "",
},
{
"name": "Angela"
}]

"lastname" is sometimes present and sometimes not and sometime is "".

I want to get all rows that have lastname not equal to "". But this does not work. It returns both the rows when lastname is "" and when lastname is not present at all. in the example above I want to only get the David node.

db.collection.find( {"lastname": {"$ne": ""}} )

Upvotes: 71

Views: 121887

Answers (4)

Jadboy20
Jadboy20

Reputation: 23

I'm not sure if this helps, but it has worked for me. The regex .+ returns anything that contains more than 1 character, whereas .* returns 0 or more. So it won't return anything less than 0 characters.

In terms of strings containing only whitespace, I don't think this solution can handle that.

Upvotes: 1

Joao Roberto joaogameprog
Joao Roberto joaogameprog

Reputation: 151

Facing this problem I thought in another solution:

db.collection.find({"lastname": {"$gte": " "}})

With this I could get only the not empty strings, also ignoring null and not existent field, because any printable value (ASCII) has a greater value than space (32).

https://en.wikipedia.org/wiki/ASCII

Upvotes: 15

Marcos Godinho
Marcos Godinho

Reputation: 114

You can use a regex query:

db.test.find({ "lastname": /(.|\s)*\S(.|\s)*/ })

This regex matches strings beginning or ending with 0 or N whitespaces (.|\s) and it have to be one or more non-whitespaces \S in the middle.

Upvotes: 2

Kyle
Kyle

Reputation: 22278

db.collection.find({"lastname" : {"$exists" : true, "$ne" : ""}})

In the mongo shell (id's omitted to save space)

> db.collection.find()
  { "name" : "Angela" }
  { "name" : "David", "lastname" : "" }
  { "name" : "Kyle",  "lastname" : "Test" }
  { "name" : "John",  "lastname" : null }

> db.collection.find({"lastname" : {"$exists" : true, "$ne" : ""}})
  { "name" : "Kyle", "lastname" : "Test" }
  { "name" : "John",  "lastname" : null }

In case you also want to filter out matches against null values you need to adjust the criteria as follows (we can also get rid of $exists as "$ne": null takes care of this)

> db.collection.find({$and:[{"lastname": {"$ne": null}}, {"lastname": {"$ne": ""}}]})
  { "name" : "Kyle", "lastname" : "Test" }

Upvotes: 152

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