Q:

Use of collation in mongodb $regex

Since v3.4 collations are available for find operations, especially as matches for diacritic characters are concerned. While a find query with a definite value ($eq opeartor or corresponding construct) will match letters and correspondent diacritics, the same is not true if a $regex is used in order to achieve a match on a partial search string (a 'LIKE').
Is there a to make the $regex query use the collation the same way than the $eq query?
consider example collection testcoll:
{ "_id" : ObjectId("586b7a0163aff45945462bea"), "city" : "Antwerpen" }, 
{ "_id" : ObjectId("586b7a0663aff45945462beb"), "city" : "Antwërpen" }

this query will find both records
db.testcoll.find({city: 'antwerpen'}).collation({"locale" : "en_US", "strength" : 1});

the same query using a regex will not (finds the record with 'Antwerpen' only)
db.testcoll.find({city: /antwe/i}).collation({"locale" : "en_US", "strength" : 1});

A:

Documentation
Case insensitive regular expression queries generally cannot use indexes effectively. The $regex implementation is not collation-aware and is unable to utilize case-insensitive indexes.

