Attribute pattern for variable fields in MongoDB - Step-by-Step Execution

Concept Flow - Attribute pattern for variable fields

Start with collection

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Define attribute pattern

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Use $regex in query

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Match documents with variable fields

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Return matched documents

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End

This flow shows how to use a regex pattern to find documents with variable attribute values in MongoDB.

Execution Sample

MongoDB

db.collection.find({"fieldName": {$regex: /^prefix_\d+$/}})

Find documents where 'fieldName' matches a pattern like 'prefix_123'.

Execution Table

Step	Document	fieldName Value	Regex Match?	Action
1	{"fieldName": "prefix_1"}	prefix_1	Yes	Include document
2	{"fieldName": "prefix_123"}	prefix_123	Yes	Include document
3	{"fieldName": "prefix_abc"}	prefix_abc	No	Exclude document
4	{"fieldName": "other_123"}	other_123	No	Exclude document
5	{"fieldName": "prefix_4567"}	prefix_4567	Yes	Include document
6	No more documents			Stop search

💡 No more documents to check, query ends.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	Final
fieldName		prefix_1	prefix_123	prefix_abc	other_123	prefix_4567	prefix_4567
Match Result		Yes	Yes	No	No	Yes	Yes

Key Moments - 2 Insights

Why does 'prefix_abc' not match the regex pattern?

Because the regex /^prefix_\d+$/ expects digits after 'prefix_', but 'abc' are letters, so it fails (see execution_table row 3).

What happens when a document's fieldName does not start with 'prefix_'?

It does not match the regex and is excluded from results (see execution_table row 4).

Visual Quiz - 3 Questions

Look at the execution_table, which document is included at step 2?

A {"fieldName": "prefix_abc"}

B {"fieldName": "prefix_123"}

C {"fieldName": "other_123"}

D {"fieldName": "prefix_4567"}

💡 Hint

Check the 'Document' and 'Action' columns at step 2 in execution_table.

At which step does the regex match fail because of letters instead of digits?

A Step 4

B Step 1

C Step 3

D Step 5

💡 Hint

Look at 'Regex Match?' column in execution_table for step 3.

If the regex was changed to /^prefix_\w+$/, which step's result would change?

A Step 3 would match

B Step 4 would match

C Step 1 would not match

D No changes

💡 Hint

Consider that \w matches letters and digits, so 'prefix_abc' would match.

Concept Snapshot

MongoDB attribute pattern matching:
Use $regex in find queries to match variable field values.
Syntax: {field: {$regex: /pattern/}}
Example: /^prefix_\d+$/ matches 'prefix_' followed by digits.
Only documents with matching fields are returned.
Useful for flexible attribute names or values.

Full Transcript

This visual execution shows how MongoDB uses regex patterns to find documents with variable attribute values. Starting with a collection, we define a regex pattern to match field values like 'prefix_123'. The query checks each document's fieldName against the regex. Documents matching the pattern are included in results; others are excluded. The execution table traces each document's fieldName and whether it matches. Variable tracker shows how fieldName and match results change step by step. Key moments clarify why some values fail to match and how the regex works. The quiz tests understanding of matching steps and regex changes. This helps beginners see how MongoDB queries can flexibly find documents with variable fields.