ProductEntityContentsResolver.cs

public class ProductEntityContentsResolver : RenderingContentsResolver
{
    private readonly IProductService _productService;
    
    public ProductEntityContentsResolver(IProductService productService)
    {
        _productService = productService;
    }

    protected override Item GetContextItem(Rendering rendering, IRenderingConfiguration renderingConfig)
    {
        if (!Context.PageMode.IsNormal)
        {
            // Always return with a default Product item if the page is in edit/preview mode
            return _productService.GetFallbackProductEntity();
        }

        if (Context.Item == null
            || HttpContext.Current?.Request?.Path == null
            || Context.Item.TemplateID.ToString() != Templates.ProductDetailsPage.Id)
        {
            return Context.Item;
        }

        var productId = GetProductId(HttpContext.Current.Request.QueryString["item"]);
        if (string.IsNullOrEmpty(productId))
        {
            return Context.Item;
        }

        var productEntity = _productService.SearchForProductEntity(productId);
        if (productEntity == null)
        {
            return Context.Item;
        }

        return productEntity;
    }

    protected override JObject ProcessItem(Item item, Rendering rendering, IRenderingConfiguration renderingConfig)
    {
        var contextItemJson = base.ProcessItem(item, rendering, renderingConfig);

        // Return only dynamic content if no datasource is set
        if (string.IsNullOrEmpty(rendering?.DataSource)
            || !ID.TryParse(rendering.DataSource, out ID datasourceId))
            return contextItemJson;

        var datasourceItem = Context.Database.GetItem(datasourceId);
        if (datasourceItem == null) return contextItemJson;

        var datasourceItemJson = base.ProcessItem(datasourceItem, rendering, renderingConfig);
        if (datasourceItemJson == null) return contextItemJson;

        if (contextItemJson != null)
        {
            contextItemJson.Merge(
                datasourceItemJson,
                new JsonMergeSettings { MergeArrayHandling = MergeArrayHandling.Union });
                
            return contextItemJson;
        }
        else
        {
            // If contextItem is empty, fallback to the datasourceItem
            return datasourceItemJson;
        }
    }

    private string GetProductId(string path)
    {
        var id = path?.Split('/').Last();
        return id ?? string.Empty;
    }
}