added macro to show how contracts work in samples/model_governance fo…

…lder

models/_samples/model_governance/how_contracts_work_columns_spec_ddl.sql

@@ -0,0 +1,91 @@
+--this is the macro dbt uses under the hood to enforce contracts. as-is in this 
+-- project, it does not affect anything. it's here for display only. 
+{%- macro get_table_columns_and_constraints() -%}
+  {{ adapter.dispatch('get_table_columns_and_constraints', 'dbt')() }}
+{%- endmacro -%}
+
+{% macro default__get_table_columns_and_constraints() -%}
+  {{ return(table_columns_and_constraints()) }}
+{%- endmacro %}
+
+{% macro table_columns_and_constraints() %}
+  {# loop through user_provided_columns to create DDL with data types and constraints #}
+    {%- set raw_column_constraints = adapter.render_raw_columns_constraints(raw_columns=model['columns']) -%}
+    {%- set raw_model_constraints = adapter.render_raw_model_constraints(raw_constraints=model['constraints']) -%}
+    (
+    {% for c in raw_column_constraints -%}
+      {{ c }}{{ "," if not loop.last or raw_model_constraints }}
+    {% endfor %}
+    {% for c in raw_model_constraints -%}
+        {{ c }}{{ "," if not loop.last }}
+    {% endfor -%}
+    )
+{% endmacro %}
+
+{%- macro get_assert_columns_equivalent(sql) -%}
+  {{ adapter.dispatch('get_assert_columns_equivalent', 'dbt')(sql) }}
+{%- endmacro -%}
+
+{% macro default__get_assert_columns_equivalent(sql) -%}
+  {{ return(assert_columns_equivalent(sql)) }}
+{%- endmacro %}
+
+{#
+  Compares the column schema provided by a model's sql file to the column schema provided by a model's schema file.
+  If any differences in name, data_type or number of columns exist between the two schemas, raises a compiler error
+#}
+{% macro assert_columns_equivalent(sql) %}
+
+  {#-- First ensure the user has defined 'columns' in yaml specification --#}
+  {%- set user_defined_columns = model['columns'] -%}
+  {%- if not user_defined_columns -%}
+      {{ exceptions.raise_contract_error([], []) }}
+  {%- endif -%}
+
+  {#-- Obtain the column schema provided by sql file. #}
+  {%- set sql_file_provided_columns = get_column_schema_from_query(sql, config.get('sql_header', none)) -%}
+  {#--Obtain the column schema provided by the schema file by generating an 'empty schema' query from the model's columns. #}
+  {%- set schema_file_provided_columns = get_column_schema_from_query(get_empty_schema_sql(user_defined_columns)) -%}
+
+  {#-- create dictionaries with name and formatted data type and strings for exception #}
+  {%- set sql_columns = format_columns(sql_file_provided_columns) -%}
+  {%- set yaml_columns = format_columns(schema_file_provided_columns)  -%}
+
+  {%- if sql_columns|length != yaml_columns|length -%}
+    {%- do exceptions.raise_contract_error(yaml_columns, sql_columns) -%}
+  {%- endif -%}
+
+  {%- for sql_col in sql_columns -%}
+    {%- set yaml_col = [] -%}
+    {%- for this_col in yaml_columns -%}
+      {%- if this_col['name'] == sql_col['name'] -%}
+        {%- do yaml_col.append(this_col) -%}
+        {%- break -%}
+      {%- endif -%}
+    {%- endfor -%}
+    {%- if not yaml_col -%}
+      {#-- Column with name not found in yaml #}
+      {%- do exceptions.raise_contract_error(yaml_columns, sql_columns) -%}
+    {%- endif -%}
+    {%- if sql_col['formatted'] != yaml_col[0]['formatted'] -%}
+      {#-- Column data types don't match #}
+      {%- do exceptions.raise_contract_error(yaml_columns, sql_columns) -%}
+    {%- endif -%}
+  {%- endfor -%}
+
+{% endmacro %}
+
+{% macro format_columns(columns) %}
+  {% set formatted_columns = [] %}
+  {% for column in columns %}
+    {%- set formatted_column = adapter.dispatch('format_column', 'dbt')(column) -%}
+    {%- do formatted_columns.append(formatted_column) -%}
+  {% endfor %}
+  {{ return(formatted_columns) }}
+{% endmacro %}
+
+{% macro default__format_column(column) -%}
+  {% set data_type = column.dtype %}
+  {% set formatted = column.column.lower() ~ " " ~ data_type %}
+  {{ return({'name': column.name, 'data_type': data_type, 'formatted': formatted}) }}
+{%- endmacro -%}