Mongo DB and Java ends with Regex

Question

I am trying to get all documents from my database where the page path ends with a certain expression using this code:

query.put(pagepath, new BasicDBObject(
"$regex", "/(" +expression+ ")$/"));

and where expression is replaced by values like ".html", ".JSON", "contact/", "/"... I get no errors but no results either, even though, when I test my regex on https://regex101.com/ it works and one of the links at least matchs.

Try expression + "$". Also, you'd need to escape the . somehow. So, perhaps, BasicDBObject query = new BasicDBObject(); and then query.put(pagepath, Pattern.compile(Pattern.quote(expression)+"$")); — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jun 17, 2016 at 10:07
tanks but It did not work and I have my query looking like this: { "\"pagepath\"" : { "$regex" : "\\Q.html\\E$"}} — Chayma Atallah
– Chayma Atallah, Commented Jun 17, 2016 at 10:19
Should the column names be inside literal double quotes? Anyway, the regex seems correct now. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jun 17, 2016 at 10:20

Wiktor Stribiżew · Accepted Answer · 2016-06-24 10:25:00Z

2

The solution that will account for any special characters in the expression and potential newline symbols in the string is

query.put(pagepath, new BasicDBObject("$regex", "(?s).*" + Pattern.quote(expression) + "$"));

Four points are:

You need to match the entire string, so you need to use .* before the expression
If a string has newlines, you need to pass the (?s) DOTALL modifier so that . could also match newline symbols
You need to Pattern.quote the expression so that it works correctly with queries that have, say, [ in them
You do not need ( and ) around expression as this capturing group is not used anywhere later.

answered Jun 24, 2016 at 10:25

Wiktor Stribiżew

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Chayma Atallah · Accepted Answer · 2016-06-22 15:43:03Z

-1

This is the solution : query.put(pagepath, new BasicDBObject("$regex", ".*(" + expression + ")$"));

answered Jun 22, 2016 at 15:43

Chayma Atallah

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1 Comment

Wiktor Stribiżew Over a year ago

Ok, that means you need to match the entire string, matches() in the background. Still, this is not fully correct approach, because you need to quote the expression, else, if it contains special regex metacharacters, you will get an error.

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