Return null for queryables for unknown collections

Don't generate valid queryables for collections which don't exist in the
database.

Author: mmcfarland

sql/002a_queryables.sql

@@ -133,25 +133,37 @@ CREATE TRIGGER queryables_collection_trigger AFTER INSERT OR UPDATE ON collectio
 FOR EACH STATEMENT EXECUTE PROCEDURE queryables_trigger_func();
 
 CREATE OR REPLACE FUNCTION get_queryables(_collection_ids text[] DEFAULT NULL) RETURNS jsonb AS $$
-    SELECT
-        jsonb_build_object(
-            '$schema', 'http://json-schema.org/draft-07/schema#',
-            '$id', 'https://example.org/queryables',
-            'type', 'object',
-            'title', 'Stac Queryables.',
-            'properties', jsonb_object_agg(
-                name,
-                definition
-            )
-        )
-        FROM queryables
-        WHERE
-            _collection_ids IS NULL OR
-            cardinality(_collection_ids) = 0 OR
-            collection_ids IS NULL OR
-            _collection_ids && collection_ids
-        ;
-$$ LANGUAGE SQL STABLE;
+BEGIN
+    -- Build up queryables if the input contains valid collection ids or is empty
+    IF (select array_agg(id) from collections) @> _collection_ids OR
+        _collection_ids IS NULL OR
+        cardinality(_collection_ids) = 0
+    THEN
+        RETURN (
+            SELECT
+                jsonb_build_object(
+                    '$schema', 'http://json-schema.org/draft-07/schema#',
+                    '$id', 'https://example.org/queryables',
+                    'type', 'object',
+                    'title', 'STAC Queryables.',
+                    'properties', jsonb_object_agg(
+                        name,
+                        definition
+                    )
+                )
+                FROM queryables
+                WHERE
+                    _collection_ids IS NULL OR
+                    cardinality(_collection_ids) = 0 OR
+                    collection_ids IS NULL OR
+                    _collection_ids && collection_ids
+        );
+    ELSE
+        RETURN NULL;
+    END IF;
+END;
+
+$$ LANGUAGE PLPGSQL STABLE;
 
 CREATE OR REPLACE FUNCTION get_queryables(_collection text DEFAULT NULL) RETURNS jsonb AS $$
     SELECT

test/pgtap/002a_queryables.sql

@@ -26,3 +26,18 @@ SELECT results_eq(
     $$ SELECT stac_search_to_where('{"filter":{"eq":[{"property":"properties.eo:cloud_cover"},0]}}'); $$,
     'Make sure that CQL filter works the same with/without properties prefix.'
 );
+
+DELETE FROM collections WHERE id = 'pgstac-test-collection';
+\copy collections (content) FROM 'test/testdata/collections.ndjson';
+
+SELECT results_eq(
+    $$ SELECT get_queryables('pgstac-test-collection') -> 'properties' ? 'id'; $$,
+    $$ SELECT true; $$,
+    'Make sure valid schema object is returned for a existing collection.'
+);
+
+SELECT results_eq(
+    $$ SELECT get_queryables('foo'); $$,
+    $$ SELECT NULL::jsonb; $$,
+    'Make sure null is returned for a non-existant collection.'
+);