Regular Expressions are frequently used in all languages to search for a pattern or word in any string. MongoDB also provides functionality of regular expression for string pattern matching using the $regex operator. MongoDB uses PCRE (Perl Compatible Regular Expression) as regular expression language.
Unlike text search, we do not need to do any configuration or command to use regular expressions.
Consider the subsequent document structure under posts collection containing the post text and its tags −
{
“post_text”: “enjoy the mongodb articles on tecklearn”,
“tags”: [
“mongodb”,
“tecklearn”
]
}

Using regex Expression

The subsequent regex query searches for all the posts containing string tecklearn in it −
>db.posts.find({post_text:{$regex:”tecklearn”}})
The same query can also be written as −
>db.posts.find({post_text:/tecklearn/})

Using regex Expression with Case Insensitive

To make the search case insensitive, we use the $options parameter with value $i. The subsequent command will look for strings having the word tecklearn, irrespective of smaller or capital case −
>db.posts.find({post_text:{$regex:”tecklearn”,$options:”$i”}})
One of the results returned from this query is that the subsequent document which contains the word tecklearn in different cases −
{
“_id” : ObjectId(“53493d37d852429c10000004”),
“post_text” : “hey! this is my post on Tecklearn”,
“tags” : [ “tecklearn” ]
}

Using regex for Array Elements

We can also use the concept of regex on array field. This is particularly very important when we implement the functionality of tags. So, if you want to search for all the posts having tags beginning from the word tutorial (either tutorial or tutorials or tutorialpoint or tutorialphp), you can use the subsequent code −
>db.posts.find({tags:{$regex:”tutorial”}})

Optimizing Regular Expression Queries

• If the document fields are indexed, the query will use make use of indexed values to match the regular expression. This makes the search very fast as compared to the regular expression scanning the whole collection.
• If the regular expression is a prefix expression, all the matches are meant to start with a certain string characters. For e.g., if the regex expression is ^tut, then the query has to search for only those strings that begin with tut.

MongoDB – Text Search

Starting from version 2.4, MongoDB started supporting text indexes to search inside string content. The Text Search uses stemming techniques to look for specified words in the string fields by dropping stemming stop words like a, an, the, etc. At present, MongoDB supports around 15 languages.

Enabling Text Search

Initially, Text Search was an experimental feature but starting from version 2.6, the configuration is enabled by default. But if you’re using the previous version of MongoDB, you have to enable text search with the subsequent code −
>db.adminCommand({setParameter:true,textSearchEnabled:true})

Creating Text Index

Consider the subsequent document under posts collection containing the post text and its tags −
{
“post_text”: “enjoy the mongodb articles on tecklearn”,
“tags”: [
“mongodb”,
“tecklearn”
]
}
We will create a text index on post_text field so that we can search inside our posts’ text −
>db.posts.ensureIndex({post_text:”text”})

Using Text Index

Now that we have created the text index on post_text field, we will search for all the posts having the word tecklearn in their text.
>db.posts.find({$text:{$search:”tecklearn”}})
The above command returned the subsequent result documents having the word tecklearn in their post text −
{
“_id” : ObjectId(“53493d14d852429c10000002”),
“post_text” : “enjoy the mongodb articles on tecklearn”,
“tags” : [ “mongodb”, “tecklearn” ]
}
{
“_id” : ObjectId(“53493d1fd852429c10000003”),
“post_text” : “writing tutorials on mongodb”,
“tags” : [ “mongodb”, “tutorial” ]
}
If you’re using old versions of MongoDB, you have to use the subsequent command −
>db.posts.runCommand(“text”,{search:” tecklearn “})
Using Text Search highly improves the search efficiency as compared to normal search.

Deleting Text Index

To delete an existing text index, first find the name of index using the subsequent query −
>db.posts.getIndexes()
After getting the name of your index from above query, run the subsequent command. Here, post_text_text is that the name of the index.
>db.posts.dropIndex(“post_text_text”)

So, this brings us to the end of blog. This Tecklearn ‘How to use Regex Expressions and Text Search in MongoDB’ helps you with commonly asked questions if you are looking out for a job in MongoDB and No-SQL Database Domain.
If you wish to learn and build a career in MongoDB or No-SQL Database domain, then check out our interactive, MongoDB Training, that comes with 24*7 support to guide you throughout your learning period. Please find the link for course details:

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Introduction to MongoDB and Importance of NoSQL
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• Introduction to JSON and BSON documents
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