Expression attribute names in DynamoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an expression attribute name for the reserved word "Name".

DynamoDB

expression_attribute_names = {"[1]": "Name"}

Drag options to blanks, or click blank then click option'

A"Name"

B"$Name"

C"#N"

D"Name#"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the actual attribute name without a placeholder.

Using a placeholder without the # symbol.

In DynamoDB, expression attribute names use placeholders starting with a hash (#) to avoid conflicts with reserved words. So "#N" is correct for "Name".

2fill in blank

medium

Complete the code to use the expression attribute name placeholder in the UpdateExpression.

DynamoDB

update_expression = "SET [1] = :val"

Drag options to blanks, or click blank then click option'

A"#N"

B"$Name"

C":Name"

D"Name"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the actual attribute name instead of the placeholder.

Using a colon (:) instead of a hash (#) for the placeholder.

The UpdateExpression must use the placeholder defined in expression attribute names, which starts with #, so "#N" is correct.

3fill in blank

hard

Fix the error in the expression attribute names dictionary key for the reserved word "Status".

DynamoDB

expression_attribute_names = {"[1]": "Status"}

Drag options to blanks, or click blank then click option'

A"#S"

B"#Status"

C"Status"

D"$Status"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the attribute name without #.

Using a placeholder starting with $ instead of #.

The key must be a short placeholder starting with #, so "#S" is correct. Using the full word with # is allowed but usually shortened for clarity.

4fill in blank

hard

Fill both blanks to define expression attribute names and use them in a FilterExpression.

DynamoDB

expression_attribute_names = {"[1]": "Date", "[2]": "Status"}
filter_expression = "[1] = :date_val AND [2] = :status_val"

Drag options to blanks, or click blank then click option'

A"#D"

B"Date"

C"#S"

D"Status"

Attempts:

3 left

💡 Hint

Common Mistakes

Using actual attribute names in the filter expression instead of placeholders.

Using placeholders without #.

Expression attribute names use placeholders starting with #. So #D for Date and #S for Status are correct. The filter expression uses these placeholders.

5fill in blank

hard

Fill all three blanks to define expression attribute names, use them in a ProjectionExpression, and in a ConditionExpression.

DynamoDB

expression_attribute_names = {"[1]": "User", "[2]": "Role", "[3]": "Access"}
projection_expression = "[1], [2]"
condition_expression = "attribute_exists([3])"

Drag options to blanks, or click blank then click option'

A"#U"

B"#R"

C"#A"

D"User"

Attempts:

3 left

💡 Hint

Common Mistakes

Using actual attribute names in expressions instead of placeholders.

Using inconsistent placeholders between dictionary and expressions.

Use placeholders starting with # for expression attribute names. #U for User, #R for Role, and #A for Access are correct. These placeholders are used in the expressions.

Practice

1. What is the main purpose of using Expression Attribute Names in DynamoDB queries?

easy

A. To increase read capacity units

B. To encrypt data before storing in DynamoDB

C. To create indexes on tables automatically

D. To safely use reserved words or special characters in attribute names

Solution

1. Step 1: Understand reserved words in DynamoDB

   DynamoDB has reserved words that cannot be used directly as attribute names in expressions.

2. Step 2: Role of Expression Attribute Names

   Expression Attribute Names let you replace reserved words or special characters with placeholders starting with # to avoid syntax errors.

3. Final Answer:

   To safely use reserved words or special characters in attribute names -> Option D

4. Quick Check:

   Expression Attribute Names = safe reserved word usage [OK]

Hint: Use #name to replace reserved words in expressions [OK]

Common Mistakes:

• Thinking they encrypt data
• Confusing with indexes
• Using them to increase capacity

2. Which of the following is the correct way to use an expression attribute name for the reserved word status in a DynamoDB UpdateExpression?

easy

A. UpdateExpression: SET #st = :val with ExpressionAttributeNames: {"#st": "status"}

B. UpdateExpression: SET status = :val

C. UpdateExpression: SET :st = :val

D. UpdateExpression: SET status# = :val

Solution

1. Step 1: Identify correct syntax for Expression Attribute Names

   Expression Attribute Names start with # and map to real attribute names in ExpressionAttributeNames dictionary.

2. Step 2: Match syntax with reserved word usage

   UpdateExpression: SET #st = :val with ExpressionAttributeNames: {"#st": "status"} correctly uses #st as placeholder for "status" and defines it in ExpressionAttributeNames.

3. Final Answer:

   UpdateExpression: SET #st = :val with ExpressionAttributeNames: {"#st": "status"} -> Option A

4. Quick Check:

   #placeholder = real name syntax [OK]

Hint: Always prefix attribute names with # in expressions [OK]

Common Mistakes:

• Using reserved word directly without #
• Using : instead of # for attribute names
• Appending # after attribute name

3. Given the following DynamoDB query snippet:

FilterExpression: "#yr = :yearVal"
ExpressionAttributeNames: {"#yr": "year"}
ExpressionAttributeValues: {":yearVal": 2023}

What will this filter expression do?

medium

A. Filter items where attribute 'year' equals 2023

B. Filter items where attribute '#yr' equals 2023

C. Cause a syntax error due to missing # in ExpressionAttributeValues

D. Filter items where attribute 'yearVal' equals 2023

Solution

1. Step 1: Understand ExpressionAttributeNames mapping

   #yr is a placeholder for the attribute name "year" to avoid reserved word conflicts.

2. Step 2: Understand FilterExpression logic

   The filter checks if the attribute "year" equals the value 2023 provided by :yearVal.

3. Final Answer:

   Filter items where attribute 'year' equals 2023 -> Option A

4. Quick Check:

   #yr = year, :yearVal = 2023 [OK]

Hint: Match #name to real attribute, :value to actual value [OK]

Common Mistakes:

• Confusing placeholders with actual attribute names
• Thinking #yr is literal attribute
• Mixing ExpressionAttributeNames and Values

4. You wrote this DynamoDB update:

UpdateExpression: "SET #nm = :nameVal"
ExpressionAttributeNames: {"#name": "name"}
ExpressionAttributeValues: {":nameVal": "Alice"}

Why does this cause an error?

medium

A. ExpressionAttributeValues key ':nameVal' is invalid

B. ExpressionAttributeNames key '#name' does not match placeholder '#nm' in UpdateExpression

C. UpdateExpression cannot use SET with placeholders

D. Missing reserved word declaration

Solution

1. Step 1: Compare placeholders in UpdateExpression and ExpressionAttributeNames

   UpdateExpression uses #nm but ExpressionAttributeNames defines #name, causing mismatch.

2. Step 2: Understand placeholder mapping requirement

   Placeholders must match exactly between expression and attribute names dictionary.

3. Final Answer:

   ExpressionAttributeNames key '#name' does not match placeholder '#nm' in UpdateExpression -> Option B

4. Quick Check:

   Placeholder names must match exactly [OK]

Hint: Match #placeholder names exactly in all places [OK]

Common Mistakes:

• Mismatching placeholder names
• Assuming :value keys cause error
• Thinking SET can't use placeholders

5. You want to update the attribute named order (a reserved word) and the attribute order#count (which contains a special character) in a DynamoDB item. Which is the correct way to write the UpdateExpression and ExpressionAttributeNames?

hard

A. UpdateExpression: "SET #ord = :val1, #ord#count = :val2" with ExpressionAttributeNames: {"#ord": "order", "#ord#count": "order#count"}

B. UpdateExpression: "SET order = :val1, order#count = :val2" with no ExpressionAttributeNames

C. UpdateExpression: "SET #o = :val1, #c = :val2" with ExpressionAttributeNames: {"#o": "order", "#c": "order#count"}

D. UpdateExpression: "SET #order = :val1, #order#count = :val2" with ExpressionAttributeNames: {"#order": "order", "#order#count": "order#count"}

Solution

1. Step 1: Understand reserved words and special characters handling

   Reserved words and special characters must be replaced with placeholders starting with # in expressions.

2. Step 2: Check placeholder naming rules

   Placeholders cannot contain special characters like #, so #order#count is invalid. Use simple placeholders like #o and #c.

3. Step 3: Verify ExpressionAttributeNames mapping

   UpdateExpression: "SET #o = :val1, #c = :val2" with ExpressionAttributeNames: {"#o": "order", "#c": "order#count"} correctly maps #o to "order" and #c to "order#count" with valid placeholder names.

4. Final Answer:

   UpdateExpression: "SET #o = :val1, #c = :val2" with ExpressionAttributeNames: {"#o": "order", "#c": "order#count"} -> Option C

5. Quick Check:

   Use simple # placeholders, map special names correctly [OK]

Hint: Use simple # placeholders; avoid special chars in placeholder names [OK]

Common Mistakes:

• Using special characters in placeholder names
• Not using ExpressionAttributeNames for reserved words
• Trying to use attribute names directly with special chars