Controllers – Insert

[HttpPost]
[ProducesResponseType(201, Type = typeof(Product))]
public async Task<ActionResult<Product>> AddNewProduct(Product product) {
    Product product = await _productRepository.AddNewProduct(product);
    return Created("api/products/{product.id}", product);
}

public interface IProductsRepository
{
    Task<List<Product>> GetAllProducts();
    Task<Product?> GetProductById(int id);
    Task DeleteProduct(int id);
    Task<Product?> UpdateProduct(int id, Product product);
    Task<Product> AddNewProduct(Product product);
}

public Task<Product> AddNewProduct(Product product) {
    var newId = this._products.Max(x => x.id) + 1;
    var productToInsert = product with { id = newId };
    _products.Add(productToInsert);
    return Task.FromResult(productToInsert);
}