Handle BigQuery non-string option 'max_staleness' (#237)

* Handle BigQuery non-string option 'max_staleness'

* Integration test for max_staleness BigQuery option

integration_tests/models/plugins/bigquery/bigquery_external.yml

@@ -67,6 +67,16 @@ sources:
         columns: *cols-of-the-people
         tests: *equal-to-the-people
 
+      - name: people_csv_with_max_staleness
+        external:
+          location: 'gs://dbt-external-tables-testing/csv/*'
+          options:
+            format: csv
+            skip_leading_rows: 1
+            max_staleness: INTERVAL 1 HOUR
+        columns: *cols-of-the-people
+        tests: *equal-to-the-people
+
 #      - name: people_json_unpartitioned
 #        external: &json-people
 #          location: 'gs://dbt-external-tables-testing/json/*'

macros/plugins/bigquery/create_external_table.sql

@@ -4,6 +4,7 @@
     {%- set external = source_node.external -%}
     {%- set partitions = external.partitions -%}
     {%- set options = external.options -%}
+    {%- set non_string_options = ['max_staleness'] %}
 
     {% if options is mapping and options.get('connection_name', none) %}
         {% set connection_name = options.pop('connection_name') %}
@@ -38,7 +39,7 @@
             uris = [{%- for uri in uris -%} '{{uri}}' {{- "," if not loop.last}} {%- endfor -%}]
             {%- if options is mapping -%}
             {%- for key, value in options.items() if key != 'uris' %}
-                {%- if value is string -%}
+                {%- if value is string and key not in non_string_options -%}
                 , {{key}} = '{{value}}'
                 {%- else -%}
                 , {{key}} = {{value}}