Calling macros across projects in dbt - Time & Space Complexity

Time Complexity: Calling macros across projects

O(n)

Understanding Time Complexity

When using dbt, calling macros from other projects can affect how long your code takes to run.

We want to know how the time to run grows when calling macros across projects.

Scenario Under Consideration

Analyze the time complexity of the following dbt code snippet.

    {{
      project_macro('argument')
    }}

    {% macro project_macro(arg) %}
      {{ other_project.some_macro(arg) }}
    {% endmacro %}
    

This code calls a macro from another project inside a macro in the current project.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Calling a macro from another project once per invocation.
• How many times: Once each time the macro is called in the model or another macro.

How Execution Grows With Input

Each time you call the macro, dbt looks up and runs the other project's macro.

Input Size (n)	Approx. Operations
10	10 macro calls, 10 cross-project lookups
100	100 macro calls, 100 cross-project lookups
1000	1000 macro calls, 1000 cross-project lookups

Pattern observation: The time grows directly with how many times you call the macro.

Final Time Complexity

Time Complexity: O(n)

This means the time to run grows linearly with the number of macro calls across projects.

Common Mistake

[X] Wrong: "Calling a macro from another project is instant and has no cost."

[OK] Correct: Each cross-project macro call requires dbt to find and run that macro, which takes time proportional to how often it is called.

Interview Connect

Understanding how calling macros across projects affects performance shows you can think about how code structure impacts run time, a useful skill in real projects.

Self-Check

"What if the macro called from the other project itself calls multiple macros inside it? How would the time complexity change?"

Practice

1. What is the main reason to call macros across different dbt projects?

easy

A. To make the project run slower

B. To increase the size of the project

C. To reuse code and keep projects organized

D. To avoid using any dependencies

Solution

1. Step 1: Understand the purpose of macros

   Macros are reusable pieces of code that help avoid repetition.

2. Step 2: Recognize the benefit of calling macros across projects

   Calling macros across projects allows sharing code, which keeps projects clean and organized.

3. Final Answer:

   To reuse code and keep projects organized -> Option C

4. Quick Check:

   Code reuse = To reuse code and keep projects organized [OK]

Hint: Macros help reuse code across projects easily [OK]

Common Mistakes:

• Thinking macros increase project size
• Believing macros slow down the project
• Ignoring the need for dependencies

2. Which syntax correctly calls a macro named calculate_total from a project named sales_project?

easy

A. {{ sales_project.calculate_total() }}

B. {{ calculate_total() }}

C. {% sales_project.calculate_total() %}

D. {{ sales_project->calculate_total() }}

Solution

1. Step 1: Recall the correct macro call syntax

   Macros from other projects are called using {{ project_name.macro_name() }}.

2. Step 2: Match the syntax to the options

   {{ sales_project.calculate_total() }} uses the correct dot notation and double curly braces.

3. Final Answer:

   {{ sales_project.calculate_total() }} -> Option A

4. Quick Check:

   Use dot notation inside {{ }} = {{ sales_project.calculate_total() }} [OK]

Hint: Use {{ project_name.macro_name() }} to call macros [OK]

Common Mistakes:

• Using {% %} instead of {{ }} for macro calls
• Missing the project name before the macro
• Using incorrect symbols like ->

3. Given the following packages.yml snippet and macro call, what will happen?

packages:
  - package: sales_project
    version: 1.0.0

-- In a model SQL file:
SELECT {{ sales_project.calculate_discount(100) }} AS discount_amount

medium

A. The macro will run and return the discount value

B. Error because the macro call syntax is wrong

C. Error because sales_project is not added as a dependency

D. The SQL will run but ignore the macro call

Solution

1. Step 1: Check the packages.yml for dependencies

   The sales_project is listed as a dependency, so it is available.

2. Step 2: Verify the macro call syntax

   The macro is called correctly using {{ sales_project.calculate_discount(100) }}.

3. Final Answer:

   The macro will run and return the discount value -> Option A

4. Quick Check:

   Dependency + correct syntax = macro runs [OK]

Hint: Add project in packages.yml before calling macros [OK]

Common Mistakes:

• Forgetting to add dependency in packages.yml
• Using wrong macro call syntax
• Assuming macro calls run without dependencies

4. You try to call a macro from another project but get an error. Which of these is the most likely cause?

medium

A. The macro name is misspelled in the call

B. You used single curly braces instead of double

C. The macro is called without parentheses

D. The other project is not listed in packages.yml

Solution

1. Step 1: Identify common errors in cross-project macro calls

   Missing the other project in packages.yml means dbt cannot find the macro.

2. Step 2: Compare other options

   Misspelling or syntax errors cause different errors, but missing dependency is most common.

3. Final Answer:

   The other project is not listed in packages.yml -> Option D

4. Quick Check:

   Missing dependency = macro call error [OK]

Hint: Always add dependencies in packages.yml first [OK]

Common Mistakes:

• Ignoring packages.yml dependencies
• Using wrong macro call syntax
• Forgetting parentheses in macro calls

5. You want to call a macro format_date from a project utils_project inside your project. You added utils_project in packages.yml. Which is the correct way to pass a date string '2024-01-01' to the macro and use its result in a model?

hard

A. SELECT {{ utils_project.format_date(`2024-01-01`) }} AS formatted_date

B. SELECT {{ utils_project.format_date("2024-01-01") }} AS formatted_date

C. SELECT {{ utils_project.format_date(2024-01-01) }} AS formatted_date

D. SELECT {{ utils_project.format_date('2024-01-01') AS formatted_date }}

Solution

1. Step 1: Confirm dependency is added

   utils_project is added in packages.yml, so macro can be called.

2. Step 2: Check correct string passing in macro call

   Strings in Jinja macros should be double-quoted inside {{ }} to avoid syntax issues.

3. Step 3: Validate SQL syntax

   SELECT {{ utils_project.format_date("2024-01-01") }} AS formatted_date correctly uses double quotes inside the macro call and proper SQL aliasing.

4. Final Answer:

   SELECT {{ utils_project.format_date("2024-01-01") }} AS formatted_date -> Option B

5. Quick Check:

   Double quotes for strings in macro calls = SELECT {{ utils_project.format_date("2024-01-01") }} AS formatted_date [OK]

Hint: Use double quotes for string args inside {{ }} [OK]

Common Mistakes:

• Using unquoted strings causing errors
• Incorrect SQL alias syntax
• Missing quotes or wrong quote types