CODEWITHSUNDEEP
c#mongodbmongodb-querymongodb-.net-driver
Erick Tejada
Erick Tejada

Reputation: 271

How to test that a string field in a MongoDB document is not empty?

I am trying to get the number of documents that have a field with an empty string. This field, lets call it "Field_One" is present in all documents (so, to be clear, I am not trying to find if the field exists or not, I want to find which documents have nothing (empty string) in field "Field_One".

I tried using (using the C# driver):

collection.Find(Query.NE("Field_One", BsonNull.Value)).Count()
collection.Find(Query.NE("Field_One", BsonString.Null)).Count()

and even (someone suggested this somewhere):

collection.Find(Query.GT("Field_One", BsonString.Empty)).Count()

But it doesn't work (they return all the documents).

Also, as a related question: Is this the best way to get the number of matching documents in a collection? As far as I understand this, it wont actually retrieve the documents from the database to my program, so the count calculation is done in the MongoDB server.

Upvotes: 7

Views: 16269

Answers (3)

malla
malla

Reputation: 1708

Assuming that you are querying for documents of a class looking something like:

public class MyClass {
        public string Field_One { get; set; }
        //... other attributes, constructors, methods etc...
}

You can also write your query using expression lambdas like this for example:

var res = collection.Find(Query<MyClass>.NE(m => m.Field_One, BsonString.Empty)).Count();

Upvotes: 0

AirBorne04
AirBorne04

Reputation: 593

BsonNull.Value translates into null
BsonString.Empty translates into ""
BsonObject.Create("") translates into "" as well

 collection.Find(Query.NE("Field_One", BsonString.Empty)).Count()

translates into "Field_One": { "$ne": "" } what should be exactly what you are looking for if the field is actually filled with ""

Upvotes: 13

user2909737
user2909737

Reputation: 635

In order to test a string isn't empty, in Javascript it is simply :

collection.find({Field_One:{ $ne: "" }})

see $ne. I can't help you translating that into C# driver language.

Upvotes: 7

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