Snowflake: Add expression parameter to columns

integration_tests/models/plugins/snowflake/snowflake_external.yml

@@ -20,6 +20,11 @@ sources:
             data_type: varchar(64)
           - name: email
             data_type: varchar(64)
+          - name: email domain
+            data_type: varchar(64)
+            quote: true
+            identifier: email
+            expression: split_part(value:email::VARCHAR, '@', 2)
         tests: &equal-to-the-people
           - dbt_utils.equality:
               compare_model: ref('people')

macros/plugins/snowflake/create_external_table.sql

@@ -29,9 +29,22 @@
                 {%- set column_alias = column.alias if column.alias else column.name %}
                 {%- set column_alias_quoted = adapter.quote(column_alias) if column.quote else column_alias %}
                 {%- set column_quoted = adapter.quote(column.name) if column.quote else column.name %}
+                {%- set column_identifier -%}
+                    {%- if 'identifier' in column and column.quote -%}
+                        {{adapter.quote(column.identifier)}}
+                    {%- elif 'identifier' in column -%}
+                        {{column.identifier}}
+                    {%- else -%}
+                        {{column_quoted}}
+                    {%- endif -%}
+                {%- endset %}
                 {%- set col_expression -%}
-                    {%- set col_id = 'value:c' ~ loop.index if is_csv else 'value:' ~ column_quoted -%}
-                    (case when is_null_value({{col_id}}) or lower({{col_id}}) = 'null' then null else {{col_id}} end)
+                    {%- if column.expression -%}
+                        {{column.expression}}
+                    {%- else -%}
+                        {%- set col_id = 'value:c' ~ loop.index if is_csv else 'value:' ~ column_identifier -%}
+                        (case when is_null_value({{col_id}}) or lower({{col_id}}) = 'null' then null else {{col_id}} end)
+                    {%- endif -%}
                 {%- endset %}
                 {{column_alias_quoted}} {{column.data_type}} as ({{col_expression}}::{{column.data_type}})
                 {{- ',' if not loop.last -}}

sample_sources/snowflake.yml

@@ -32,6 +32,18 @@ sources:
           - name: etl_tstamp
             data_type: timestamp
             description: "Timestamp event began ETL"
+          - name: etl timestamp
+            # Use double-quoted identifiers for name and identifier
+            quote: true
+            # Specifying identifier lets us rename etl_tstamp to "etl timestamp"
+            identifier: etl_tstamp
+            data_type: timestamp
+            description: "Timestamp event began ETL with a double quoted identifier"
+          - name: etl_date
+            data_type: date
+            description: "Date event began ETL"
+            # Expressions can manipulate the variant value prior to casting to data_type.
+            expression: TRY_TO_DATE(VALUE:etl_tstamp::VARCHAR, 'YYYYMMDD')
           - name: contexts
             data_type: variant
             description: "Contexts attached to event by Tracker"