[GitHub] [arrow-adbc] lidavidm commented on a diff in pull request #577: feat(c/driver/postgresql): Implement GetTableSchema

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

lidavidm commented on code in PR #577:
URL: https://github.com/apache/arrow-adbc/pull/577#discussion_r1186013361


##########
c/driver/postgresql/connection.cc:
##########
@@ -47,7 +71,76 @@ AdbcStatusCode PostgresConnection::GetTableSchema(const char* catalog,
                                                   const char* table_name,
                                                   struct ArrowSchema* schema,
                                                   struct AdbcError* error) {
-  return ADBC_STATUS_NOT_IMPLEMENTED;
+  AdbcStatusCode final_status = ADBC_STATUS_OK;
+  struct StringBuilder query = {0};
+  if (StringBuilderInit(&query, /*initial_size=*/256) != 0) return ADBC_STATUS_INTERNAL;
+
+  if (StringBuilderAppend(
+          &query, "%s",
+          "SELECT attname, atttypid "
+          "FROM pg_catalog.pg_class AS cls "
+          "INNER JOIN pg_catalog.pg_attribute AS attr ON cls.oid = attr.attrelid "
+          "INNER JOIN pg_catalog.pg_type AS typ ON attr.atttypid = typ.oid "
+          "WHERE attr.attnum >= 0 AND cls.oid = '") != 0)
+    return ADBC_STATUS_INTERNAL;
+
+  if (db_schema != nullptr) {
+    char* schema = PQescapeIdentifier(conn_, db_schema, strlen(db_schema));
+    if (schema == NULL) {
+      SetError(error, "%s%s", "Faled to escape schema: ", PQerrorMessage(conn_));
+      return ADBC_STATUS_INVALID_ARGUMENT;
+    }
+
+    int ret = StringBuilderAppend(&query, "%s%s", schema, ".");
+    PQfreemem(schema);
+
+    if (ret != 0) return ADBC_STATUS_INTERNAL;
+  }
+
+  char* table = PQescapeIdentifier(conn_, table_name, strlen(table_name));
+  if (table == NULL) {
+    SetError(error, "%s%s", "Failed to escape table: ", PQerrorMessage(conn_));
+    return ADBC_STATUS_INVALID_ARGUMENT;
+  }
+
+  int ret = StringBuilderAppend(&query, "%s%s", table_name, "'::regclass::oid");
+  PQfreemem(table);
+
+  if (ret != 0) 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);
+    ArrowSchemaInit(schema);

Review Comment:
   Ah, yeah. Though that got removed by the other refactor anyways.



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