Template
single collection
multiple collections
mgodatagen
update
indexe
explain
Stage
Database
bson
mgodatagen
[{first:"John",last:"Smith"},{first:"Alice",last:"Johnson"},{first:"Bob",last:"Williams"},]
Query
db.collection.find({$expr:{$regexMatch:{input:{$concat:["$first"," ","$last"]},regex:"a",options:"i"}}})
Result