feat: clickhouse safe_cast macro

[MaelleBaillet5]

Summary

Add clickhouse__safe_cast macro that automatically provides default values for ClickHouse types when casting null values. This eliminates the need to specify all non-nullable columns in unit test fixtures.

Fixes #315

Checklist

Delete items not relevant to your PR:

• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG
• For significant changes, documentation in https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials

[CLAassistant]

All committers have signed the CLA.

[windsurf-bot]

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[windsurf-bot]

The condition field == 'null' checks if the field is literally the string 'null', not if it's a SQL NULL value. For SQL NULL values, you should use {{ field }} is null instead. The current implementation will only work if 'null' is passed as a string literal.

[MaelleBaillet5]

You're correct that the condition field == 'null' checks for the literal string 'null' rather than a SQL NULL value. This is actually intentional for this macro's specific use case.
The safe_cast macro is designed specifically to solve issue #315 - handling non-nullable ClickHouse columns in dbt unit tests.

[koletzilla]

Hi @MaelleBaillet5 ! Thanks for contributing this. This PR is looking nice and I'd like to merge it ASAP.

The only thing I'm missing now is a proper test for the unit-testing part. As you mention, this is specifically designed to solve the issue in #315, so it would be great to add a test to ensure #315 is not happening again. I think creating an additional test and adding there the unit-test listed in the "Steps to reproduce" section would be enough. Would you add it?

[MaelleBaillet5]

/windsurf-review

[windsurf-bot]

Other comments (2)

• tests/integration/adapter/utils/test_safe_cast.py (151-151) Missing newline at the end of file. Adding a newline at the end of files is a common convention that helps with text processing tools and version control systems.
• tests/integration/adapter/utils/test_safe_cast.py (87-87) Use lowercase `false` for boolean literals to follow Python style conventions.

          assert result[10] == false  # Bool default
  

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[windsurf-bot]

The current implementation only handles the literal string 'null', but might miss actual null values passed as variables. Consider enhancing the implementation to also check for actual null values:

Suggested change

	{% macro clickhouse__safe_cast(field, dtype) %}
	{%- if field == 'null' -%}
	CAST(defaultValueOfTypeName('{{ dtype }}') AS {{ dtype }})
	{%- else -%}
	CAST({{ field }} AS {{ dtype }})
	{%- endif -%}
	{% endmacro %}
	{% macro clickhouse__safe_cast(field, dtype) %}
	{%- if field is none or field == 'null' -%}
	CAST(defaultValueOfTypeName('{{ dtype }}') AS {{ dtype }})
	{%- else -%}
	CAST({{ field }} AS {{ dtype }})
	{%- endif -%}
	{% endmacro %}

[MaelleBaillet5]

The safe_cast macro is exclusively designed for dbt unit test fixtures, where
all values are passed as string literals from YAML files. When a column is omitted
in a fixture, dbt-core's get_empty_schema_sql macro passes the literal string
'null' (not a SQL NULL value).

[windsurf-bot]

This test method should also use the shared fixture to avoid running the model again.

Suggested change

	def test_safe_cast_types(self, project):
	"""Test that safe_cast preserves the expected data types"""
	# Run the model
	results = run_dbt(["run", "--select", "safe_cast_test"])
	assert len(results) == 1
	def test_safe_cast_types(self, project, run_model):
	"""Test that safe_cast preserves the expected data types"""
	# Get column types from ClickHouse

[MaelleBaillet5]

• I modified the macro because I had a bug with a DataTime(“Paris/Europe”) type and added this case to the tests.
• I added the requested unit test, but is it in the right folder?
• I saw that the CI is not passing. I don't have this problem locally, but I tried to adapt it. We'll see if it passes in the CI.