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Why are we trying to use $eq operator in example of "Matching a Regular Expression"?

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#1 
db.tasks.find({     status: {         $eq: new RegExp("pending", "ig")    } });

Above expression does not return anything.
However, if you will try like this

    db.tasks.find({status: new RegExp("pendi", "ig")});

It will return all tasks with “pending” status.

#2

Hi @Manjeet_Kumar !!
The reason the first expression does not return anything while the second one does is because of the regular expression pattern being used.

In the first expression, status: { $eq: new RegExp("pending", "ig") }, the regular expression pattern is "pending", which means it will match the exact string “pending” case-insensitively ("i" flag) in the status field. However, if the status field contains any additional characters before or after the word “pending”, it won’t be considered a match.

On the other hand, in the second expression, status: new RegExp("pendi", "ig"), the regular expression pattern is "pendi". This pattern will match any occurrence of “pendi” (case-insensitively) within the status field. So if the status field contains “pending” or “suspended” or any other value that includes “pendi” as a substring, it will be considered a match.

To make the first expression behave like the second one and match any occurrence of “pending” within the status field, you can modify it as follows:

db.tasks.find({ status: new RegExp("pending", "ig") });

This will use the regular expression pattern "pending", allowing it to match any occurrence of “pending” case-insensitively in the status field.
I hope it helps. Happy Learning :blush:

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#3

Somehow, i am not able to understand the importance of $eq operator.
For example:

db.tasks.find({    'assignee.username': { $eq: 'user_a' },})

Gives the same result as

db.tasks.find({'assignee.username': "user_a"});

I want to understand what difference does $eq makes?

Course: MongoDB: The Complete Guide - Learn Interactively
Lesson: Read Documents: Part 1 - MongoDB: The Complete Guide

#4

In MongoDB, the $eq operator is used for exact equality comparison within query conditions. It is the default behavior for equality comparison, so when you write a query without any operator, like {'assignee.username': "user_a"}, it is equivalent to using $eq.

The $eq operator is particularly useful in scenarios where you want to explicitly specify the equality comparison and differentiate it from other comparison operators. It can be especially helpful when constructing complex queries that involve multiple operators.

Here’s an example to illustrate the use of $eq in a more expressive manner:

db.tasks.find({
  'assignee.username': { $eq: 'user_a' },
  'status': { $eq: 'completed' },
  'priority': { $eq: 1 }
});

In this example, the query is filtering documents where the assignee.username field is equal to 'user_a', the status field is equal to 'completed', and the priority field is equal to 1. By explicitly using the $eq operator, you are clarifying the intent of exact equality comparison.

However, since $eq is the default operator for equality comparison, it is not necessary to use it explicitly unless you want to make your query more explicit or you are combining multiple operators in the same query condition.

In summary, using $eq operator explicitly can enhance the readability of your queries, but for simple equality comparisons, it is not required as MongoDB assumes equality by default.
I hope it helps. Happy Learning :blush:

1 Like