Use MongoDB Search for Full-Text Regex Queries

Avoid Inefficient Regex Matching

If you frequently run case-insensitive regex queries (utilizing the i option), we recommend using MongoDB Search queries that use the $search aggregation pipeline stage.

You can specify collation on an index to define language-specific rules for string comparison, such as rules for lettercase and accent marks. However, collation can cause some functionality loss compared to MongoDB Search queries. In non MongoDB Search environments, case-insensitive indexes do not improve performance for regex queries. The $regex query operator is not collation-aware, and cannot use case-insensitive indexes effectively. MongoDB Search indexes significantly improve the performance of case-sensitive queries and offer more options for customizing query parameters.

Example

Consider an employees collection with the following documents. This collection has no indexes besides the default _id index:

// employees collection
{
  "_id": 1,
  "first_name": "Hannah",
  "last_name": "Simmons",
  "dept": "Engineering"
},
{
  "_id": 2,
  "first_name": "Michael",
  "last_name": "Hughes",
  "dept": "Security"
},
{
  "_id": 3,
  "first_name": "Wendy",
  "last_name": "Crawford",
  "dept": "Human Resources"
},
{
  "_id": 4,
  "first_name": "MICHAEL",
  "last_name": "FLORES",
  "dept": "Sales"
}

If your application frequently queries the first_name field, you may want to run case-insensitive regex queries to more easily find matching names. Case-insensitive regex also matches against differing data formats, as in the example above where you have first_names of both "Michael" and "MICHAEL". However, we recommend MongoDB Search queries that use the $search aggregation pipeline stage.

If a user searches for the string "michael", the application may run the following query:

db.employees.find( { first_name: { $regex: /michael/i } } )

Since this query specifies the $regex option i, it is case-insensitive. The query returns the following documents:

{ "_id" : 2, "first_name" : "Michael", "last_name" : "Hughes", "dept" : "Security" }
{ "_id" : 4, "first_name" : "MICHAEL", "last_name" : "FLORES", "dept" : "Sales" }

Although this query does return the expected documents, case-insensitive regex queries with no index support are not very performant. To improve performance, create a MongoDB Search index:

{
  "mappings": {
    "dynamic": true
  }
}

Collation can cause some functionality loss. When the strength field of an index's collation document is 1 or 2, the index is case-insensitive. For a detailed description of the collation document and the different strength values, see Collation Document.

For the application to use the case-insensitive index, you must also specify the same collation document from the index in the regex query. While you can remove the $regex operator from the previous find() method and use the newly created index, we recommend that you use an MongoDB Search query that uses the $search aggregation pipeline stage.

db.employees.find( { first_name: "michael" } ).collation( { locale: 'en', strength: 2 } )

db.employees.aggregate([
  {
    $search: {
      "index": "default",
      "text": {
        "path": "first_name",
        "query": "michael"
      }
    }
  }
])

Learn More

• To learn more about MongoDB Search queries, see Queries and Indexes.

• To learn more about case-insensitive indexes with illustrative examples, see Case Insensitive Indexes.

• To learn more about regex queries in MongoDB, see $regex.

• MongoDB University offers a free course on optimizing MongoDB Performance. To learn more, see Monitoring and Insights.