Added numerous operations like concat(...), coalesce(...), abs(...), etc (#20)

tests/postgres/test_group_by_with_operations.cpp

@@ -0,0 +1,72 @@
+#ifndef SQLGEN_BUILD_DRY_TESTS_ONLY
+
+#include <gtest/gtest.h>
+
+#include <ranges>
+#include <rfl.hpp>
+#include <rfl/json.hpp>
+#include <sqlgen.hpp>
+#include <sqlgen/postgres.hpp>
+#include <vector>
+
+namespace test_group_by_with_operations {
+
+struct Person {
+  sqlgen::PrimaryKey<uint32_t> id;
+  std::string first_name;
+  std::string last_name;
+  int age;
+};
+
+TEST(postgres, test_group_by) {
+  static_assert(std::ranges::input_range<sqlgen::Range<Person>>,
+                "Must be an input range.");
+
+  const auto people1 = std::vector<Person>(
+      {Person{
+           .id = 0, .first_name = "Homer", .last_name = "Simpson", .age = 45},
+       Person{.id = 1, .first_name = "Bart", .last_name = "Simpson", .age = 10},
+       Person{.id = 2, .first_name = "Lisa", .last_name = "Simpson", .age = 8},
+       Person{
+           .id = 3, .first_name = "Maggie", .last_name = "Simpson", .age = 0}});
+
+  const auto credentials = sqlgen::postgres::Credentials{.user = "postgres",
+                                                         .password = "password",
+                                                         .host = "localhost",
+                                                         .dbname = "postgres"};
+
+  using namespace sqlgen;
+
+  struct Children {
+    std::string last_name;
+    std::string last_name_trimmed;
+    double avg_age;
+    double max_age_plus_one;
+    double min_age_plus_one;
+  };
+
+  const auto get_children =
+      select_from<Person>(
+          "last_name"_c, trim("last_name"_c).as<"last_name_trimmed">(),
+          max(cast<double>("age"_c) + 1.0).as<"max_age_plus_one">(),
+          (min(cast<double>("age"_c)) + 1.0).as<"min_age_plus_one">(),
+          round(avg(cast<double>("age"_c))).as<"avg_age">()) |
+      where("age"_c < 18) | group_by("last_name"_c) | to<std::vector<Children>>;
+
+  const auto children = postgres::connect(credentials)
+                            .and_then(drop<Person> | if_exists)
+                            .and_then(write(std::ref(people1)))
+                            .and_then(get_children)
+                            .value();
+
+  EXPECT_EQ(children.size(), 1);
+  EXPECT_EQ(children.at(0).last_name, "Simpson");
+  EXPECT_EQ(children.at(0).last_name_trimmed, "Simpson");
+  EXPECT_EQ(children.at(0).avg_age, 6.0);
+  EXPECT_EQ(children.at(0).max_age_plus_one, 11.0);
+  EXPECT_EQ(children.at(0).min_age_plus_one, 1.0);
+}
+
+}  // namespace test_group_by_with_operations
+
+#endif