Built-in roles (read, readWrite, dbAdmin) in MongoDB - Step-by-Step Execution

Concept Flow - Built-in roles (read, readWrite, dbAdmin)

Start: User needs permissions

↓

Choose built-in role

↓

read

↓

Access granted based on role

↓

End

User selects one built-in role to get specific database permissions: read, readWrite, or dbAdmin.

Execution Sample

MongoDB

use mydb
 db.createUser({
   user: "alice",
   roles: ["readWrite"]
 })

Creates user 'alice' with readWrite role on 'mydb' allowing read and write access.

Execution Table

Step	Action	Role Assigned	Permissions Granted	Result
1	Switch to database 'mydb'	N/A	N/A	Context set to 'mydb'
2	Create user 'alice' with role 'readWrite'	readWrite	Read and write data on 'mydb'	User 'alice' created
3	User 'alice' tries to read data	readWrite	Allowed	Read operation successful
4	User 'alice' tries to write data	readWrite	Allowed	Write operation successful
5	User 'alice' tries to perform admin task	readWrite	Denied	Operation failed: insufficient privileges
6	End	N/A	N/A	User permissions enforced based on role

💡 User permissions are enforced according to the assigned built-in role.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
user	undefined	alice (readWrite)	alice (readWrite)	alice (readWrite)	alice (readWrite)
permissions	none	read and write	read allowed	read and write allowed	read and write allowed

Key Moments - 2 Insights

Why can't 'alice' perform admin tasks with the readWrite role?

Because the readWrite role only grants read and write data permissions, not administrative privileges. See execution_table row 5 where admin tasks are denied.

What happens if you assign the 'read' role instead of 'readWrite'?

The user can only read data but cannot write. This is shown by the difference in permissions granted in execution_table rows 3 and 4.

Visual Quiz - 3 Questions

Look at the execution_table, what permissions does 'alice' have after step 2?

A Read and write data on 'mydb'

B Only read data on 'mydb'

C Full admin privileges

D No permissions

💡 Hint

Check the 'Permissions Granted' column at step 2 in the execution_table.

At which step does 'alice' fail to perform an operation due to insufficient privileges?

A Step 3

B Step 4

C Step 5

D Step 6

💡 Hint

Look for 'Operation failed' in the 'Result' column of the execution_table.

If 'alice' was assigned the 'dbAdmin' role, which permission would change?

A She could only read data

B She could manage database structure

C She would lose write access

D No change in permissions

💡 Hint

Refer to the concept_flow where dbAdmin role allows managing database structure.

Concept Snapshot

Built-in roles in MongoDB control user permissions.
read: can only read data.
readWrite: can read and write data.
dbAdmin: can manage database structure.
Assign roles when creating users to control access.
Permissions are enforced automatically by MongoDB.

Full Transcript

This visual execution shows how MongoDB built-in roles work. First, you switch to the target database. Then you create a user and assign a built-in role like readWrite. This role lets the user read and write data but not perform admin tasks. The execution table traces each step: creating the user, reading data, writing data, and trying an admin task. The user can do read and write but fails admin operations. Variables track the user and permissions over time. Key moments clarify why roles limit actions and what changes if roles differ. The quiz tests understanding by asking about permissions at specific steps and role effects. The snapshot summarizes the roles and their permissions simply.

Practice

1. Which built-in MongoDB role allows a user to only view data without making any changes?

easy

A. root

B. readWrite

C. dbAdmin

D. read

Solution

1. Step 1: Understand the read role

   The read role allows users to view data but not modify it.

2. Step 2: Compare with other roles

   readWrite allows changes, dbAdmin manages settings, root has full access.

3. Final Answer:

   read -> Option D

4. Quick Check:

   View-only permission = read [OK]

Hint: View-only means read role [OK]

Common Mistakes:

• Confusing readWrite with read
• Thinking dbAdmin allows data viewing only
• Assuming root is for read-only

2. Which of the following is the correct way to assign the readWrite role to a user on the database mydb in MongoDB shell?

easy

A. db.grantRolesToUser('username', [{role: 'readWrite', db: 'mydb'}])

B. db.createUser({user: 'username', roles: ['readWrite']})

C. db.grantRolesToUser('username', ['readWrite'])

D. db.grantRolesToUser('username', [{role: 'readWrite', db: 'admin'}])

Solution

1. Step 1: Check syntax for granting roles

   The correct syntax uses db.grantRolesToUser with an array of role objects specifying role and database.

2. Step 2: Validate database name and role format

   db.grantRolesToUser('username', [{role: 'readWrite', db: 'mydb'}]) correctly specifies role as 'readWrite' and database as 'mydb'. db.grantRolesToUser('username', [{role: 'readWrite', db: 'admin'}]) wrongly uses 'admin' database.

3. Final Answer:

   db.grantRolesToUser('username', [{role: 'readWrite', db: 'mydb'}]) -> Option A

4. Quick Check:

   Grant role with role+db object array [OK]

Hint: Use role objects with db name in array for granting roles [OK]

Common Mistakes:

• Passing roles as simple strings without db
• Using wrong database name for the role
• Using createUser instead of grantRolesToUser for existing users

3. Given a user with the dbAdmin role on database sales, which of the following actions can the user perform?

medium

A. Create and drop indexes on collections

B. Insert new documents into collections

C. Read documents from collections

D. Modify documents in collections

Solution

1. Step 1: Understand dbAdmin role capabilities

   The dbAdmin role allows managing database settings like indexes, stats, and users, but not data changes.

2. Step 2: Match actions to role permissions

   Creating/dropping indexes is a dbAdmin task. Inserting, reading, or modifying documents require readWrite or read roles.

3. Final Answer:

   Create and drop indexes on collections -> Option A

4. Quick Check:

   dbAdmin manages indexes, not data changes [OK]

Hint: dbAdmin manages indexes, not data content [OK]

Common Mistakes:

• Assuming dbAdmin can insert or modify data
• Confusing readWrite with dbAdmin
• Thinking dbAdmin can read data

4. You tried to assign the readWrite role to a user with this command:
db.grantRolesToUser('alice', ['readWrite'])
But it failed. What is the likely cause?

medium

A. The user 'alice' does not exist

B. The role array must contain objects with role and db fields

C. The readWrite role does not exist

D. You must use createUser to assign roles

Solution

1. Step 1: Check syntax for grantRolesToUser

   The method requires an array of role objects with role and db fields, not just strings.

2. Step 2: Analyze the given command

   The command uses an array of strings, which is invalid syntax and causes failure.

3. Final Answer:

   The role array must contain objects with role and db fields -> Option B

4. Quick Check:

   Roles must be objects with role and db [OK]

Hint: Roles need role+db objects, not strings [OK]

Common Mistakes:

• Passing roles as strings instead of objects
• Assuming createUser is needed to add roles to existing users
• Ignoring user existence errors

5. You want a user to manage database indexes and view data but not modify documents. Which combination of built-in roles should you assign?

hard

A. readWrite only

B. dbAdmin only

C. read and dbAdmin

D. readWrite and dbAdmin

Solution

1. Step 1: Identify roles for viewing data and managing indexes

   read allows viewing data, dbAdmin allows managing indexes and database settings.

2. Step 2: Exclude roles that allow modifying documents

   readWrite allows modifying documents, which is not desired here.

3. Final Answer:

   read and dbAdmin -> Option C

4. Quick Check:

   View + manage indexes = read + dbAdmin [OK]

Hint: Combine read and dbAdmin to view and manage without edits [OK]

Common Mistakes:

• Using readWrite which allows document changes
• Assigning only dbAdmin which lacks read permission
• Assuming dbAdmin includes readWrite