Спроектируйте тестируемый сервис продуктов поверх БД

Задача

Реализуйте:

• Структуру Product (id, name, price, category)
• Структуру ProductFilter (опциональная категория, максимальная цена)
• Интерфейс IProductRepository с методом fetchByFilter
• Заглушку FakeProductRepository для тестов
• Сервис ProductService, который использует репозиторий и выводит продукты

Решение

#include <iostream>
#include <string>
#include <vector>
#include <optional>
#include <memory>
#include <algorithm>
#include <cassert>

// --- Domain types ---

struct Product {
    int         id;
    std::string name;
    double      price;
    std::string category;
};

struct ProductFilter {
    std::optional<std::string> category;
    std::optional<double>      maxPrice;
};

// --- Repository interface ---

class IProductRepository {
public:
    virtual ~IProductRepository() = default;
    virtual std::vector<Product> fetchByFilter(const ProductFilter& f) const = 0;
};

// --- Fake for tests ---

class FakeProductRepository : public IProductRepository {
public:
    void add(Product p) { products_.push_back(std::move(p)); }

    std::vector<Product> fetchByFilter(const ProductFilter& f) const override {
        std::vector<Product> result;
        for (const auto& p : products_) {
            if (f.category && p.category != *f.category) continue;
            if (f.maxPrice  && p.price    >  *f.maxPrice)  continue;
            result.push_back(p);
        }
        return result;
    }

private:
    std::vector<Product> products_;
};

// --- Real repository (stub — actual SQL omitted) ---

class SqlProductRepository : public IProductRepository {
public:
    explicit SqlProductRepository(const std::string& /*connStr*/) {}

    std::vector<Product> fetchByFilter(const ProductFilter& /*f*/) const override {
        // In production: build SQL WHERE clause, execute query, map rows to Product.
        return {};
    }
};

// --- Service ---

class ProductService {
public:
    explicit ProductService(IProductRepository& repo) : repo_(repo) {}

    void printByFilter(const ProductFilter& f) const {
        auto products = repo_.fetchByFilter(f);
        if (products.empty()) {
            std::cout << "(no products match the filter)\n";
            return;
        }
        for (const auto& p : products)
            std::cout << "[" << p.id << "] " << p.name
                      << " | " << p.category
                      << " | $" << p.price << '\n';
    }

private:
    IProductRepository& repo_;
};

// --- Tests ---

static void testFilterByCategory() {
    FakeProductRepository repo;
    repo.add({1, "Widget",  9.99,  "tools"});
    repo.add({2, "Gadget", 19.99,  "electronics"});
    repo.add({3, "Doohickey", 4.99, "tools"});

    auto results = repo.fetchByFilter({.category = "tools"});
    assert(results.size() == 2);
    assert(results[0].name == "Widget");
    assert(results[1].name == "Doohickey");
}

static void testFilterByMaxPrice() {
    FakeProductRepository repo;
    repo.add({1, "Cheap", 5.0,  "misc"});
    repo.add({2, "Mid",  15.0,  "misc"});
    repo.add({3, "Pricey", 50.0, "misc"});

    auto results = repo.fetchByFilter({.maxPrice = 20.0});
    assert(results.size() == 2);
}

static void testNoResults() {
    FakeProductRepository repo;
    repo.add({1, "Widget", 9.99, "tools"});

    auto results = repo.fetchByFilter({.category = "food"});
    assert(results.empty());
}

int main() {
    testFilterByCategory();
    testFilterByMaxPrice();
    testNoResults();
    std::cout << "All tests passed\n\n";

    // Service demo
    FakeProductRepository repo;
    repo.add({1, "Hammer",   12.50, "tools"});
    repo.add({2, "Keyboard", 89.00, "electronics"});
    repo.add({3, "Screwdriver", 7.99, "tools"});

    ProductService svc(repo);
    std::cout << "--- tools under $15 ---\n";
    svc.printByFilter({.category = "tools", .maxPrice = 15.0});
    return 0;
}

Ключевые моменты