MongoDB: Is it possible to make a case-insensitive query?

Question

Example:

> db.stuff.save({\"foo\":\"bar\"});

> db.stuff.find({\"foo\":\"bar\"}).count();
1
> db.stuff.find({\"foo\":\"BAR\"}).count();
0
         


        

Answer 1

Starting with MongoDB 3.4, the recommended way to perform fast case-insensitive searches is to use a Case Insensitive Index.

I personally emailed one of the founders to please get this working, and he made it happen! It was an issue on JIRA since 2009, and many have requested the feature. Here's how it works:

A case-insensitive index is made by specifying a collation with a strength of either 1 or 2. You can create a case-insensitive index like this:

db.cities.createIndex(
  { city: 1 },
  { 
    collation: {
      locale: 'en',
      strength: 2
    }
  }
);

You can also specify a default collation per collection when you create them:

db.createCollection('cities', { collation: { locale: 'en', strength: 2 } } );

In either case, in order to use the case-insensitive index, you need to specify the same collation in the find operation that was used when creating the index or the collection:

db.cities.find(
  { city: 'new york' }
).collation(
  { locale: 'en', strength: 2 }
);

This will return "New York", "new york", "New york" etc.

Other notes

• The answers suggesting to use full-text search are wrong in this case (and potentially dangerous). The question was about making a case-insensitive query, e.g. username: 'bill' matching BILL or Bill, not a full-text search query, which would also match stemmed words of bill, such as Bills, billed etc.

• The answers suggesting to use regular expressions are slow, because even with indexes, the documentation states:

  "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."

  $regex answers also run the risk of user input injection.