Refactoring: Add new template_t class for rendering SQL templates

Separates the generic template code cleanly from any SQL details.

Author: joto

CMakeLists.txt

@@ -268,6 +268,7 @@ else()
                 src/gen/gen-tile.cpp
                 src/gen/params.cpp
                 src/gen/raster.cpp
+                src/gen/template.cpp
                 src/gen/tracer.cpp)
     target_link_libraries(osm2pgsql-gen osm2pgsql_lib ${LIBS} ${POTRACE_LIBRARY} ${OpenCV_LIBS})
 endif()

src/gen/gen-base.cpp

@@ -11,8 +11,7 @@
 
 #include "format.hpp"
 #include "params.hpp"
-
-#include <fmt/args.h>
+#include "template.hpp"
 
 #include <cassert>
 
@@ -84,43 +83,20 @@ std::string gen_base_t::context()
     return gen_name.empty() ? "" : fmt::format(" '{}'", gen_name);
 }
 
-namespace {
-
-pg_result_t dbexec_internal(
-    pg_conn_t const &connection, std::string const &templ,
-    fmt::dynamic_format_arg_store<fmt::format_context> const &format_store)
-{
-    try {
-        auto const sql = fmt::vformat(templ, format_store);
-        return connection.exec(sql);
-    } catch (fmt::format_error const &e) {
-        log_error("Missing parameter for template: '{}'", templ);
-        throw;
-    }
-}
-
-} // anonymous namespace
-
 pg_result_t gen_base_t::dbexec(std::string const &templ)
 {
-    fmt::dynamic_format_arg_store<fmt::format_context> format_store;
-    for (auto const &[key, value] : get_params()) {
-        format_store.push_back(fmt::arg(key.c_str(), to_string(value)));
-    }
-    return dbexec_internal(connection(), templ, format_store);
+    template_t sql_template{templ};
+    sql_template.set_params(get_params());
+    return connection().exec(sql_template.render());
 }
 
 pg_result_t gen_base_t::dbexec(params_t const &tmp_params,
                                std::string const &templ)
 {
-    fmt::dynamic_format_arg_store<fmt::format_context> format_store;
-    for (auto const &[key, value] : get_params()) {
-        format_store.push_back(fmt::arg(key.c_str(), to_string(value)));
-    }
-    for (auto const &[key, value] : tmp_params) {
-        format_store.push_back(fmt::arg(key.c_str(), to_string(value)));
-    }
-    return dbexec_internal(connection(), templ, format_store);
+    template_t sql_template{templ};
+    sql_template.set_params(get_params());
+    sql_template.set_params(tmp_params);
+    return connection().exec(sql_template.render());
 }
 
 void gen_base_t::raster_table_preprocess(std::string const &table)

src/gen/template.cpp

@@ -0,0 +1,26 @@
+/**
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ * This file is part of osm2pgsql (https://osm2pgsql.org/).
+ *
+ * Copyright (C) 2006-2024 by the osm2pgsql developer community.
+ * For a full list of authors see the git log.
+ */
+
+#include "template.hpp"
+
+void template_t::set_params(params_t const &params) {
+    for (auto const &[key, value] : params) {
+        m_format_store.push_back(fmt::arg(key.c_str(), to_string(value)));
+    }
+}
+
+std::string template_t::render() const
+{
+    try {
+        return fmt::vformat(m_template, m_format_store);
+    } catch (fmt::format_error const &e) {
+        log_error("Missing parameter for template: '{}'", m_template);
+        throw;
+    }
+}

src/gen/template.hpp

@@ -0,0 +1,35 @@
+#ifndef OSM2PGSQL_TEMPLATE_HPP
+#define OSM2PGSQL_TEMPLATE_HPP
+
+/**
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ * This file is part of osm2pgsql (https://osm2pgsql.org/).
+ *
+ * Copyright (C) 2006-2024 by the osm2pgsql developer community.
+ * For a full list of authors see the git log.
+ */
+
+#include "format.hpp"
+#include "params.hpp"
+
+#include <fmt/args.h>
+
+#include <string>
+
+class template_t
+{
+public:
+    template_t(std::string_view tmpl) : m_template(tmpl) {}
+
+    void set_params(params_t const &params);
+
+    std::string render() const;
+
+private:
+    std::string m_template;
+    fmt::dynamic_format_arg_store<fmt::format_context> m_format_store;
+
+}; // class template_t
+
+#endif // OSM2PGSQL_TEMPLATE_HPP