Find mongo documents where a field contains a string pattern

This tutorial guides you to find mongo documents where a field contains a string pattern using mongodb’s regular expression capabilities.

Find mongo documents where a field contains a string

MongoDB uses Perl compatible regular expressions. You need to use $regex and the following syntax option.

{ <field>: { $regex: /pattern/<options> } }

The <options> available to use with regular expression are i(for case insensitivity), m(for patterns that include anchors i.e. ^ for the start and $ for the end), x(extended capability to ignore all white space characters in the regular expressions patterns), s(to allow dot “.” character)

For our example, you can create a sample collection called posts with data using this json. Then try the following commands and check the responses as shown below.

The following example queries all documents where a field contains string pattern “/adv/”

> db.posts.find({tags:{$regex: /adv/}}).pretty()

Response
--------

{
        "_id" : ObjectId("5063114bd386d8fadbd6b008"),
        "title" : "MongoDB Advantages",
        "description" : "Advantages of MongoDB",
        "by_user" : "sneppets",
        "url" : "https://docs.mongodb.com",
        "tags" : [
                "#mongodb",
                "#mongo_tutor",
                "#tutorials",
                "#advantages"
        ],
        "likes" : 50,
        "comments" : [
                {
                        "user" : "John",
                        "message" : "Nice tutorial",
                        "dateCreated" : ISODate("2019-02-25T02:15:00Z"),
                        "like" : 10
                },
                {
                        "user" : "Paul",
                        "message" : "Good one",
                        "dateCreated" : ISODate("2019-02-25T02:15:00Z"),
                        "like" : 12
                }
        ]
}

Further optimization can be done by using “prefix expression” in the regular expression, which means all the potential matches starts with the same string. And this allows MongoDB to construct a “range” from the prefix and find matches against those values from the index within the range.

A regular expression with “prefix expression” starts with caret (^), followed by a string. For example /^#adv/ will be optimized by finding matches against values from the range with index starting with #adv.

The following is example to demonstrate a regular expression with “prefix expression”. Note, “#” in regular expression /^#adv/ is part of the string pattern.

> db.posts.find({tags:{$regex: /^#adv/}}).pretty()

Response
--------

{
        "_id" : ObjectId("5063114bd386d8fadbd6b008"),
        "title" : "MongoDB Advantages",
        "description" : "Advantages of MongoDB",
        "by_user" : "sneppets",
        "url" : "https://docs.mongodb.com",
        "tags" : [
                "#mongodb",
                "#mongo_tutor",
                "#tutorials",
                "#advantages"
        ],
        "likes" : 50,
        "comments" : [
                {
                        "user" : "John",
                        "message" : "Nice tutorial",
                        "dateCreated" : ISODate("2019-02-25T02:15:00Z"),
                        "like" : 10
                },
                {
                        "user" : "Paul",
                        "message" : "Good one",
                        "dateCreated" : ISODate("2019-02-25T02:15:00Z"),
                        "like" : 12
                }
        ]
}

Addition to /^#adv/, the regular expressions /^#adv.*/ and /^#adv.$/ will match equivalent strings but they may have different performance characteristics.

The following example shows how to perform case insensitive regular expression match for the string.

> db.posts.find({tags:{$regex: /^#adv/i}}).pretty()

Response
--------

{
        "_id" : ObjectId("5063114bd386d8fadbd6b008"),
        "title" : "MongoDB Advantages",
        "description" : "Advantages of MongoDB",
        "by_user" : "sneppets",
        "url" : "https://docs.mongodb.com",
        "tags" : [
                "#mongodb",
                "#mongo_tutor",
                "#tutorials",
                "#advantages"
        ],
        "likes" : 50,
        "comments" : [
                {
                        "user" : "John",
                        "message" : "Nice tutorial",
                        "dateCreated" : ISODate("2019-02-25T02:15:00Z"),
                        "like" : 10
                },
                {
                        "user" : "Paul",
                        "message" : "Good one",
                        "dateCreated" : ISODate("2019-02-25T02:15:00Z"),
                        "like" : 12
                }
        ]
}

Also Read

References

MongoDB Docs