Why is my MongoDB Go Driver regex query not returning any results?

Regex Queries in MongoDB Using the Go Driver

MongoDB provides a powerful querying mechanism that allows you to retrieve documents based on various criteria. One of these criteria is regular expressions, which are often used for pattern matching and substring searches.

Problem Encountered:

When attempting to use the MongoDB Go driver to perform a regular expression query, a user encountered an issue where the expected results were not returned. Despite following the documentation's examples, the cursor remained empty.

Root Cause:

The root cause of this issue lies in the construction of the primitive.Regex struct. The Pattern field of this struct expects a regular expression pattern without leading and trailing slashes.

Solution:

To resolve this issue, remove the slashes surrounding the regular expression pattern in the primitive.Regex struct. Here's the corrected code:

<code class="go">filter := bson.D{{"text", primitive.Regex{Pattern: "he", Options: ""}}}</code>

Example:

With this corrected code, the following query should now return the expected results:

<code class="go">ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
defer cancel()

cur, err := coll.Find(ctx, filter)
if err != nil {
    fmt.Println(err)
    return
}

i := 0
for cur.Next(ctx) {
    i = i + 1
}
fmt.Println("Found", i, "elements")</code>

By removing the slashes surrounding the regular expression pattern, the primitive.Regex struct can now correctly match the desired substring in the "text" field of the documents and return the expected results.

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