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MongoDB regex and pattern matching

$regex – starts with, ends with, contains, case-insensitive.  Β·  9 practice questions  Β·  Cheat sheet ↓

$regex matches strings against a pattern, so a MongoDB regex query for "starts with", "ends with" or "contains" is a one-liner: { name: /^B/ }, { name: /e$/ }, { name: /Bar/ }. You can write the pattern as a JavaScript literal or as { $regex: "^B", $options: "i" }, where i makes it case-insensitive. The anchors ^ and $ plus the wildcard . cover most needs; everything else is ordinary regular-expression syntax.

Two practical notes. Characters like ., ( and + mean something in a pattern, so escape them with a backslash when you mean them literally. And only patterns anchored at the start (^...) can use an index; a leading wildcard scans every document, which is fine for practice collections and painful at scale.

MongoDB regex query practice questions

  1. Find restaurants whose name starts with B. easy restaurants
  2. Find restaurants whose name ends with the letter e. easy restaurants
  3. Find restaurants whose name contains Bar anywhere. easy restaurants
  4. Find restaurants whose cuisine starts with the letter C. Return name and cuisine without _id. medium restaurants
  5. Find restaurants whose address.zipcode starts with 10. medium restaurants
  6. Find restaurants whose name contains cafe, ignoring case. medium restaurants
  7. Find movies whose title contains the word the, ignoring case. Return title only, without _id. medium movies
  8. Find restaurants whose address.street ends with Ave or Blvd. hard restaurants
  9. Find restaurants whose cuisine starts with any of the letters I, J or K. hard restaurants

Each question is answered in a live mongo-shell editor on this page; the result is checked against a reference solution.

$regex cheat sheet: anchors, options, escaping

Two equivalent forms

db.restaurants.find({ name: { $regex: "^B" } })
db.restaurants.find({ name: /^B/ })

The three anchors you need

GoalPattern
starts with Bro/^Bro/
ends with Bar/Bar$/
contains Bar anywhere/Bar/
case-insensitive contains/bar/i or { $regex: "bar", $options: "i" }
starts with any of a set/^[BCD]/

Escaping

Dots, parens and $ are regex metacharacters:

{ email: /\.com$/ }     // literal dot, then "com" at the end

Gotchas

  • Only ^-anchored, case-sensitive regexes can use an index. /foo/i

scans the whole collection.

  • Regex works on strings only – it will not match a number field.

Common questions

How do I do a "starts with" query in MongoDB?

Anchor the pattern to the start: { name: /^Bar/ } or { name: { $regex: "^Bar" } }. Add the i option for case-insensitive matching: /^bar/i. Anchored prefixes can use an index on the field; unanchored patterns cannot.

How do I make a MongoDB regex case-insensitive?

Add the i flag: { cuisine: /italian/i } or { cuisine: { $regex: "italian", $options: "i" } }. For exact case-insensitive equality on many queries, a case-insensitive collation on the collection or index is the faster long-term option.

Can I use $regex on a number field?

No. $regex only matches string values; documents whose field holds a number are simply skipped. To pattern-match numbers, convert them first in an aggregation with $toString, or store a string copy of the value alongside the number.

Related topics:Comparison OperatorsFinding & Projection

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MongoDB topics:Finding & ProjectionComparison OperatorsLogical OperatorsElement & TypeSort, Limit & SkipArray QueriesEmbedded DocumentsAggregation BasicsGrouping & Accumulators$unwind & Array PipelinesJoins & Advanced StagesFull cheat sheet