Compare fullwidth and halfwidth japanese characters in mongodb by using collation and regex

Question

According to the MongoDB documentation and the ICU documentation it should be possible to ignore full-width and half-width difference in Japanese text by utilizing collation.

I tried the following;

{ locale: "ja", caseLevel:true, strength:1} 

with different strength but none of them is working.

db.getCollection('mycollection')
        .find({"desc":/ﾊﾞﾝﾄﾞ/})
        .collation({ locale: "ja", caseLevel:true, strength:1})

This query cannot get result from the following document;

{
    "desc": "＊EGRパイプバンド外れ"
}

---

update

Found reason that in MongoDB regex cannot apply collation, so if I use certain match to perform query the result is perfect:

db.getCollection('mycollection')
        .find({"desc":"*EGRﾊﾟｲﾌﾟﾊﾞﾝﾄﾞ外れ???"})
        .collation({ locale: "ja", caseLevel:true, strength:1})

This query will return ＊EGRパイプバンド外れ this result.

But not if I use regex, any suggestion on it?

Answer 1

There is no way to make collate work with any regex find logic, since the regex script will override any collate definition, and only use the logic defined within itself, namely find any string that contains half-width ﾊﾞﾝﾄﾞ only.

The simplest way to achieve this is to add an extra logic before you send the search text into your MongoDB client, and duplicate the text into both half & full width. You can use some existing tool like this.

Then apply both half & full width search parameters into your find condition with $or;

db.mycollection.find({$or: [{"desc":/ﾊﾞﾝﾄﾞ/}, {"desc":/バンド/}]}) 

Same issue;

• Use of collation in mongodb $regex