Entity Framework adding multiple related entities with single insert

Question

I have a GenericService Add method like so:-

    public bool Add(T entity, Expression<Func<T, bool>> filter = null)
    {
        try
        {
            _genericRepository.Add(entity, filter);
        }
        catch (Exception e)
        {
            return false;
        }
        return true;
    }

and a GenericRepository Add method like so:-

    public void Add(T entity, Expression<Func<T, bool>> filter = null)
    {
        var existing = Get<T>(filter);
        if (existing.Result != null) return;
        Context.Add(entity);
        Save();
    }

This is the call I am doing in the ProductsController:-

    [HttpPost]
    public IActionResult Create([FromBody] Product product)
    {
        if (product == null)
            return BadRequest();

        var result = _productsService.Add(product, m => m.Name == product.Name);
        if (result)
        {
            return CreatedAtRoute("GetProducts", new { id = product.Id }, product);

        }
        return BadRequest("Item not added");
    }

I am creating this by means of an integration test as follows :-

        testBrand = new Brand { Name = "testBrand" };
        testImage = new Image { Name = "testImage", Url = "/Brands/adidas_logo_test.png" };
        testBrand.Image = testImage;

        testCategory = new Category {Name = "testCategory"};

        testProduct = new Product
        {
            Category = testCategory,
            Name = "testProduct",
            Brand = testBrand,
            BrandId = testBrand.Id,
            CategoryId = testCategory.Id,
            Deal = false,
            Description = "testDescription",
            Discount = "50% Discount",
            Image = testImage,
            ImageId = testImage.Id,
            Price = new decimal(50.00),
            Stock = 5
        };

    [Test]
    public async Task Create_CreateAProduct_NewBrandNewCategoryNewImageProductsController()
    {
        //Arrange 

        //Act
        //create new image
        var requestImage = "api/Images/";
        var postResponseImage = await _client.PostAsJsonAsync(requestImage, testImage);
        var created = await postResponseImage.Content.ReadAsStringAsync();
        var createdImage = JsonConvert.DeserializeObject<Image>(created);

        //Act
        testBrand.Image = createdImage;
        testBrand.ImageId = createdImage.Id;
        testImage.Id = createdImage.Id;

        var postResponseProduct = await _client.PostAsJsonAsync(requestProduct, testProduct);
        var createdProduct = await postResponseProduct.Content.ReadAsStringAsync();
        var createdProductObj = JsonConvert.DeserializeObject<Product>(createdProduct);

        var getResponse = await _client.GetAsync(requestProduct + "Get/" + createdProductObj.Id);
        var fetched = await getResponse.Content.ReadAsStringAsync();
        var fetchedProduct = JsonConvert.DeserializeObject<Product>(fetched);

        // Assert
        Assert.IsTrue(postResponseProduct.IsSuccessStatusCode);
        Assert.IsTrue(getResponse.IsSuccessStatusCode);

        Assert.AreEqual(testProduct.Name, createdProductObj.Name);
        Assert.AreEqual(testProduct.Name, fetchedProduct.Name);

        Assert.AreNotEqual(Guid.Empty, createdProductObj.Id);
        Assert.AreEqual(createdProductObj.Id, fetchedProduct.Id);
    }

Everything works fine, until I try to insert an entity that has multiple related entities. Let me give an example.

Lets say I have a Product, which has an FK ImageId, a FK for BrandId, and a FK for CategoryId. The Brands entity has already a FK ImageId for the Image entity.

Now when I try to insert a new product, its inserting 2 images, one which comes with the Brand, and the image for the Product itself. So in the Images Table, I get 2 entries, when I only want 1 new entry for the Product Image. Also, this is causing a problem when I want to use an existing image for a new product.

So I was thinking of creating a new Service/Repository for the Product to Inherit from the Generic Service/Repository, and add some more logic to it. However is there a better way to do this?

Thanks for your help and time

Answer 1

Now I understood.

When using a client for testing purposes, mvc receives your request with json data, and creates your models correctly.

However, mvc doesn't know you want the same Image for product and brand, it'll create one instance for each one, like this (I simplified for example purposes):

var product = new Product();
var brand = new Brand();
product.Image = new Image();
product.Brand = brand;
brand.Image = new Image(); // new image with same info...

Likewise, entity framework will assume they are two different images with same data. Just let it know it's the same, by doing something like this in your actions (of course you would create a better code, this is just a quick sample):

[HttpPost]
public IActionResult Create([FromBody] Product product)
{
    if (product == null)
        return BadRequest();

    // If the image already exists...nullify image so EF won't try to insert a new one...
    if (product.ImageId > 0)
        product.Image = null;
    // If the image already exists...and the brand doesn't have an existing image, use the same image and nullify the brand's image as well...
    if (product.ImageId > 0 && product.Brand != null && !(product.Brand.ImageId > 0))
    {
        product.Brand.ImageId = product.ImageId;
        product.Brand = null;
    }
    // If product is reveiving a new image...and the brand doesn't have an existing image, use the same new image...
    if (product.Image != null && product.Brand != null && !(product.Brand.ImageId > 0))
        product.Brand.Image = product.Image;

    var result = _productsService.Add(product, m => m.Name == product.Name);
    if (result)
    {
        return CreatedAtRoute("GetProducts", new { id = product.Id }, product);

    }
    return BadRequest("Item not added");
}

---

Just to test in a console application I reproduced it like below. Some classes:

public class Brand
{
    public int Id { get; set; }
    public virtual Image Image { get; set; }
    public int ImageId { get; set; }

}

public class Image
{
    public int Id { get; set; }
}

public class Product
{
    public int Id { get; set; }
    public virtual Image Image { get; set; }
    public virtual Brand Brand { get; set; }
    public int ImageId { get; set; }
    public int BrandId { get; set; }
}

the DbContext with configurations:

public class MyDbContext : DbContext
{
    public DbSet<Product> Products { get; set; }

    public DbSet<Brand> Brands { get; set; }

    public DbSet<Image> Images { get; set; }

    public MyDbContext()
        : base("name=MyDbContext")
    {
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {

        modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();
        modelBuilder.Conventions.Remove<ManyToManyCascadeDeleteConvention>();
        modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();

        modelBuilder.Properties<int>().Where(p => p.Name == "Id").Configure(p => p.IsKey());
        modelBuilder.Entity<Product>().HasRequired(p => p.Brand).WithMany().HasForeignKey(p => p.BrandId);
        modelBuilder.Entity<Product>().HasRequired(p => p.Image).WithMany().HasForeignKey(p => p.ImageId);
        modelBuilder.Entity<Brand>().HasRequired(p => p.Image).WithMany().HasForeignKey(p => p.ImageId);

    }
}

Then finally, the code itself.

This first case I use the same instance:

class Program
{
    static void Main(string[] args)
    {

        using (var db = new MyDbContext())
        {

            var image = new Image();
            var product = new Product();
            var brand = new Brand();
            product.Image = image;
            product.Brand = brand;
            brand.Image = image; // same instance

            db.Products.Add(product);

            db.SaveChanges();

        }

    }
}

My result was:

Then I ran again, now using a new instance:

class Program
{
    static void Main(string[] args)
    {

        using (var db = new MyDbContext())
        {

            var image = new Image();
            var product = new Product();
            var brand = new Brand();
            product.Image = image;
            product.Brand = brand;
            brand.Image = new Image();

            db.Products.Add(product);

            db.SaveChanges();

        }

    }
}

and now we have two new images: