Regular Expressions
In a real-world movie service, you will want to provide auto-completion search boxes where, as soon as the user types in a few characters of the movie title, the search box suggests all the movies whose titles match the character sequence typed in. This is implemented using regular expressions. A regular expression is a special string that defines a character pattern. When such a regular expression is used to find string fields, all the strings that have the matching pattern are found and returned.
In MongoDB queries, regular expressions can be used with the $regex operator. Imagine you have typed the word Opera into the search box and want to find all the movies whose titles contain this character pattern. The regular expression query for this will be as follows:
db.movies.find(
{"title" : {$regex :"Opera"}}
)
Upon executing this query and using projection to print only the titles, the result will appear as follows...