当我尝试更新父实体时，实体框架正在更新子实体

Question

I have a Product entity which is mapped to Product table:

[Table("Product")]
public class Product
{
    public int Id { get; set; }
    public string Name { get; set; } 
    public decimal Price { get'; set; }
}

I also have a CombinedProduct entity which is mapped to CombinedProductView, note that this entity is only for reading, this view is not updatable :

[Table("CombinedProductView")]
public class CombinedProduct : Product
{
    public string Store { get; set; } 
}

And this is my MyDbContext :

[DbConfigurationType(typeof(MySqlEFConfiguration))]
public class MyDbContext: DbContext
{
    public MyDbContext() : base("MyDB")
    {
    }

    public DbSet<Product> Product { get; set; }
    public DbSet<CombinedProduct> CombinedProduct { get; set; }
}

I have a repository which has a method to return a List of Product s and another method for saving Product s:

Public class ProductRepository
{
    public List<Product> GetProductsMoreExpensiveThan(decimal price)
    {
        return _context.Product.AsNoTracking().Where(p => p.Price > price).ToList();
    }

    public void Update(List<Product> products)
    {
        foreach (var p in products)
        {
            _context.Product.Attach(p);
            _context.Entry(p).State = EntityState.Modified;
        }

        _context.SaveChanges();
    }
}

I want increase the price of some products by $5, so I get a list of Product s and increase the price:

var products = _productRepository.GetProductsMoreExpensiveThan(100);
foreach(var p in products)
{
    p.Price += 5;
}

_productRepository.Update(products);

This throws exception, because EF is trying to update CombinedProductView which is not updatable. Why is Entity Framework is trying to update the derived entity ( CombinedProduct ) when updating the base entity Product ?

Answer 1

I believe the confusion is coming from your base class of Product having a [Table("Product")] attribute on it, and then the derived class additionally having one.

You can use a base-class within object types in EF, however, that base class is typically NOT representing a table.

There is a lot to unwrap here as to methods of how you can manage to make this work, so rather than try to expand this into a crazy level of detail this article on Inheritance Strategies with EF should help clear it up as it provides detail on the basics for table names etc.