https://world.episerver.com/documentation/developer-guides/commerce/catalogs/Importing-catalog-data/

Some methods used in this code are not working(like:- _linksRepository.UpdateRelation)

private readonly IContentRepository contentRepository;
private readonly ILinksRepository linksRepository;
private readonly IInventoryService inventoryService;
private readonly IPriceDetailService priceDetailService;
private void AddEntry()
  {
    ContentReference parentCategoryLink; // Get a reference to the node you want to add the product to.

    // Add product
    var product = contentRepository.GetDefault<MyCustomProduct>(parentCategoryLink, CultureInfo.GetCultureInfo("en-US"));
    product.Name = "Product name";
    product.Code = "123-456";
    product.Publisher = "Episerver";
    contentRepository.Save(product, SaveAction.Publish, AccessLevel.NoAccess);

    // Add variation
    var variation = contentRepository.GetDefault<MyCustomVariation>(parentCategoryLink, CultureInfo.GetCultureInfo("en-US"));
    variation.Name = "Variation name";
    variation.Code = "654-321";
    variation.Type = "Paperback";
    variation.MaxQuantity = 50;
    contentRepository.Save(variation, SaveAction.Publish, AccessLevel.NoAccess);

    // Add relation between product and variant
    var newVariation = new ProductVariation
      {
        SortOrder = 1,
        Source = product.ContentLink,
        Target = variation.ContentLink
      };
    linksRepository.UpdateRelation(newVariation);

    // Add inventory information
    var inventoryRecord = new InventoryRecord
      {
        CatalogEntryCode = variation.Code,
        PurchaseAvailableQuantity = 10,
        PurchaseAvailableUtc = DateTime.UtcNow,
        WarehouseCode = "default"
      };
    inventoryService.Insert(new[] { inventoryRecord });
            
    // Add price information
    var priceDetailValue = new PriceDetailValue
      {
        CatalogKey = new CatalogKey(AppContext.Current.ApplicationId, variation.Code),
        MarketId = new MarketId("US"),
        CustomerPricing = CustomerPricing.AllCustomers,
        ValidFrom = DateTime.UtcNow,
        UnitPrice = new Money(1m, Currency.USD)
      };
    priceDetailService.Save(priceDetailValue);
  }