[GitHub] [arrow-adbc] WillAyd commented on a diff in pull request #676: feat(c/driver/postgres): Implement GetObjectsSchema

["WillAyd (via GitHub)" <gi...@apache.org>]

WillAyd commented on code in PR #676:
URL: https://github.com/apache/arrow-adbc/pull/676#discussion_r1190350559


##########
c/driver/postgresql/connection.cc:
##########
@@ -145,6 +145,76 @@ AdbcStatusCode PostgresConnection::GetInfo(struct AdbcConnection* connection,
   return BatchToArrayStream(&array, &schema, out, error);
 }
 
+AdbcStatusCode PostgresConnectionGetObjectsImpl(
+    PGconn* conn, int depth, const char* catalog, const char* db_schema,
+    const char* table_name, const char** table_types, const char* column_name,
+    struct ArrowSchema* schema, struct ArrowArray* array, struct AdbcError* error) {
+  RAISE_ADBC(AdbcInitConnectionObjectsSchema(schema, error));
+
+  struct ArrowError na_error = {0};
+  CHECK_NA_DETAIL(INTERNAL, ArrowArrayInitFromSchema(array, schema, &na_error), &na_error,
+                  error);
+  CHECK_NA(INTERNAL, ArrowArrayStartAppending(array), error);
+
+  struct ArrowArray* catalog_name_col = array->children[0];
+  struct ArrowArray* catalog_db_schemas_col = array->children[1];
+
+  // TODO: support proper filters
+  if (!catalog) {
+    struct StringBuilder query = {0};
+    if (StringBuilderInit(&query, /*initial_size=*/256) != 0) return ADBC_STATUS_INTERNAL;
+
+    if (StringBuilderAppend(&query, "%s", "SELECT datname FROM pg_catalog.pg_database"))
+      return ADBC_STATUS_INTERNAL;
+
+    PqResultHelper result_helper = PqResultHelper{conn, query.buffer};
+    StringBuilderReset(&query);
+    pg_result* result = result_helper.Execute();
+
+    ExecStatusType pq_status = PQresultStatus(result);
+    if (pq_status == PGRES_TUPLES_OK) {
+      int num_rows = PQntuples(result);
+      array->length = num_rows - 1;  // makes ArrowArrayFinishElement happy, but why?

Review Comment:
   Wasn't sure about this but took inspiration from a comment I saw by @paleolimbot  https://github.com/apache/arrow-nanoarrow/issues/67#issuecomment-1324185749
   
   Had to do the `-1` to get it to work with the validation checks in `ArrowArrayFinishBuildingDefault`, but admittedly don't understand the why of this



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