实体框架多对多更新而不创建重复项？

Question

I am using Entity Framework (Code-First) to create a database, part of which contains two entities with a many-to-many relationship. Here is their code:

public class Product
{
    [Key]
    public int ProductId { get; set; }

    [MaxLength(50)]
    public string CUSIP { get; set; }

    [MaxLength(50)]
    public string SEDOL { get; set; }

    [MaxLength(50)]
    public string BUID { get; set; }

    [MaxLength(50)]
    public string Key { get; set; }

    [Required]
    public bool Track { get; set; }

    [InverseProperty("Products")]
    [ForeignKey("ProductListId")]
    public virtual List<ProductList> ProductLists { get; set; }

    public override string ToString()
    {
        return String.Format("PRODUCT[ ProductId: {0}, CUSIP: {1}, SEDOL: {2}, BUID: {3}, Key: {4}, Track: {5}, ProductLists: {6} ]",
                            ProductId,
                            CUSIP,
                            SEDOL,
                            BUID,
                            Key,
                            Track,
                            (ProductLists != null ? ""+ProductLists.Count : "null"));
    }
}

public class ProductList
{
    [Key]
    public int ProductListId { get; set; }

    [Required]
    [MaxLength(50)]
    public string Name { get; set; }

    [InverseProperty("ProductLists")]
    [ForeignKey("ProductId")]
    public virtual List<Product> Products { get; set; }

    public override string ToString()
    {
        return String.Format("PRODUCT-LIST[ ProductListId: {0}, Name: {1}, Products: {2} ]",
                            ProductListId, 
                            Name,
                            (Products != null ? "" + Products.Count : "null"));
    }
}

In my repository, I am attempting to write an update method for product, such that changing the tracking Boolean or adding/removing it from a productList will save to the database. I am using AngularJS and asp.net-MVC for the rest of my project, so here is the update method in the productsController class:

    public void Put(int id, [FromBody] Product product)
    {
        _repo.UpdateProduct(id, product);
        _repo.Save();
    }

Because this is called from AngularJS, the product object is initialized from a JS object.

And finally, here's the updateProduct method in the repository:

    public bool UpdateProduct(int id, Models.Product product)
    {
        if (product != null) System.Diagnostics.Debug.WriteLine("UpdateProduct() [" + id + "]\n" + product.ToString());

        if (id == 0) return AddProduct(product);

        try
        {
            Product ctxProduct = GetProduct(id);
            if (ctxProduct != null && product != null)
            {
                ctxProduct.CUSIP = product.CUSIP;
                ctxProduct.SEDOL = product.SEDOL;
                ctxProduct.BUID = product.BUID;
                ctxProduct.Key = product.Key;
                ctxProduct.Track = product.Track;

                /*ctxProduct.ProductLists = new List<ProductList>();
                for (int i = 0; i < product.ProductLists.Count; i++)
                {
                    ctxProduct.ProductLists.Add((product.ProductLists[i].ProductListId == 0)
                                                ? product.ProductLists[i]
                                                : GetProductListIncludingProducts(product.ProductLists[i].ProductListId));

                }*/
                return true;
            }
            return false;
        }
        catch (Exception e)
        {
            System.Diagnostics.Debug.WriteLine(e.Message + "\n ----- " + e.InnerException);
            return false;
        }
    }

Right now, the section that should update the productList relations is commented out. While it's like this, I can update any other field in the product and it will work as expected.

If I uncomment this section, the code will create duplicate productLists in the database, as well as duplicates of all the products contained in those lists.

Lastly, if I replace GetProductListIncludingProducts(product.ProductLists[i].ProductListId) with GetProductList(product.ProductLists[i].ProductListId) , I get the following error from _repo.Save() :

System.Data.SqlClient.SqlException: Violation of PRIMARY KEY constraint 'PK_dbo.ProductListProducts'. Cannot insert duplicate key in object 'dbo.ProductListProducts'

GetProductListIncludingProducts() simply adds .Include("Products") in its call to the context.

I would like to get the update method to simply readjust the many to many relationship without crashing or creating a lot of duplicate data.

Answer 1

It took awhile but I finally figured it out. Turns out the problem was with my WebAPI formatter. My code was defaulting to the XMLMediaFormatter - when I was expecting it to be using my JsonMediaFormatter that I set up to handle reference tracking. In case it helps anybody, here is my final UpdateProduct method that works with the JsonMediaFormatter:

    public bool UpdateProduct(int id, Product product)
    {
        if (product != null) System.Diagnostics.Debug.WriteLine("UpdateProduct() [" + id + "] " + product.ToString());

        if (id == 0) return AddProduct(product);

        try
        {
            Product ctxProduct = GetProductIncludingProductLists(id);

            if (ctxProduct != null && product != null)
            {
                ctxProduct.CUSIP = product.CUSIP;
                ctxProduct.SEDOL = product.SEDOL;
                ctxProduct.BUID = product.BUID;
                ctxProduct.Key = product.Key;
                ctxProduct.Track = product.Track;

                ctxProduct.ProductLists = new List<ProductList>();
                foreach (ProductList pl in product.ProductLists)
                    ctxProduct.ProductLists.Add(pl.ProductListId == 0 
                                                ? pl 
                                                : GetProductList(pl.ProductListId));
                return true;
            }
            return false;
        }
        catch (Exception e)
        {
            System.Diagnostics.Debug.WriteLine("Update Product Error: " + e.Message + "\nInner: " + e.InnerException);
            return false;
        }
    }