MongoDB Text search fails for stop words - mongodb

Question

I'm trying to do a query in my collection, but its not returning anything.
Here's my query:
{'$match': {'$text': {'$search': 'a'}}},
{'$group': {'_id': {'texto': '$texto'},
'somanumero': {'$sum': '$numero'}}}
My collection:
{ "_id" : ObjectId("555cdc4fe13823315537042d"), "texto" : ObjectId("555cdc4fe13823315537042c"), "numero" : ObjectId("555cdc4fe13823315537042e") }
{ "_id" : ObjectId("555cdc5ee13823315537042f"), "numero" : 5, "texto" : "a", "lattexto" : "-15.79506", "lontexto" : "-47.88322" }
{ "_id" : ObjectId("555cdc6ae138233155370430"), "numero" : 10, "texto" : "a", "lattexto" : "-15.79506", "lontexto" : "-47.88322" }
{ "_id" : ObjectId("555cdc73e138233155370431"), "numero" : 3, "texto" : "b", "lattexto" : "-15.79506", "lontexto" : "-47.88322" }
And here's my text index:
{
"v" : 1,
"key" : {
"_fts" : "text",
"_ftsx" : 1
},
"name" : "texto_text",
"ns" : "OSA.teste_texto",
"default_language" : "portuguese",
"weights" : {
"texto" : 1
},
"language_override" : "language",
"textIndexVersion" : 2
}
When i use $group or $match alone, it works.
Am I doing something wrong?

Answer 1

From the docs:
MongoDB supports text search for various languages. text indexes drop
language-specific stop words (e.g. in English, “the”, “an”, “a”,
“and”, etc.) and uses simple language-specific suffix stemming.
The problem with your data is that some of the records have the language-specific stop word, a, which is considered to be a stop word in portugese too. Some of the stop words include, and a is on top of the list.
a
ao
aos
aquela
aquelas
aquele
aqueles
aquilo
as
até
com
como
These words are never indexed, and hence whenever you query for stop words, you get no results.
At the same time, If you query for b, you would get results, since it is not a stop word and would be indexed.