ORM for C++: Comparison and Examples

ORM for C++: Comparison and Usage Examples

Unlike dynamically typed languages (Python, PHP), C++ does not have built-in support for reflection and metaprogramming sufficient to create a "magical" ORM. Nevertheless, there are several powerful solutions that automate working with databases. In this article, we will compare three popular libraries: ODB, SOCI, and SQLiteCpp, and provide examples of their use.

Comparison Criteria

When choosing an ORM for C++, it is worth paying attention to:

Code Generation Type — external generator or C++ templates.
DBMS Support — SQLite, PostgreSQL, MySQL, Oracle.
Performance — overhead of mapping.
Integration Complexity — whether a separate build step is required.

1. ODB — Industrial ORM for C++

ODB is a commercial (with a free version for open-source) ORM based on code generation from annotated header files. It supports relational databases (SQLite, PostgreSQL, MySQL, Oracle) and even NoSQL (MongoDB).

Example with ODB (SQLite)

First, declare the entity class:

#include <odb/core.hxx>

#pragma db objectclass Person {public:    Person(const std::string& name, int age)        : name_(name), age_(age) {}

    unsigned long id() const { return id_; }    const std::string& name() const { return name_; }    int age() const { return age_; }

private:    friend class odb::access;    #pragma db id auto    unsigned long id_;    std::string name_;    int age_;};

Usage:

#include <odb/database.hxx>#include <odb/sqlite/database.hxx>#include <odb/transaction.hxx>#include "person.hxx"#include "person-odb.hxx"

int main() {    auto db = std::make_shared<odb::sqlite::database>("test.db");    odb::transaction t(db->begin());

    Person p("Alice", 30);    db->persist(p); // INSERT

    auto result = db->query<Person>(        odb::query<Person>::age > 25);    for (const auto& person : result) {        std::cout << person.name() << std::endl;    }    t.commit();}

Pros: full object model, relationship support, lazy loading. Cons: requires a code generator (build step), commercial license.

2. SOCI — Lightweight "Data Access Layer"

SOCI is not a full-fledged ORM, but a library for working with SQL from C++ that provides a convenient syntax for executing queries and mapping results. It works with SQLite, PostgreSQL, MySQL, Oracle, and ODBC.

Example with SOCI

#include <soci/soci.h>#include <soci/sqlite3/soci-sqlite3.h>#include <iostream>

struct Person {    int id;    std::string name;    int age;};

int main() {    soci::session sql(soci::sqlite3, "test.db");    sql << "CREATE TABLE IF NOT EXISTS person ("           "id INTEGER PRIMARY KEY, "           "name TEXT, age INTEGER)";

    // Insert    sql << "INSERT INTO person (name, age) VALUES (:name, :age)",        soci::use("Bob"), soci::use(25);

    // Query with mapping to struct    Person p;    soci::indicator ind;    sql << "SELECT id, name, age FROM person WHERE id = :id",        soci::use(1), soci::into(p.id), soci::into(p.name, ind), soci::into(p.age);

    if (ind == soci::i_ok) {        std::cout << p.name << " " << p.age << std::endl;    }}

Pros: easy integration, no code generation, support for prepared statements. Cons: no automatic object mapping