在 Entity Framework 核心中更新多对多

Question

以下是相关类及其配置：

public class Product 
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public long ProductId { get; set; }

    [Required]
    public string ProductName { get; set; }

    public ICollection<ProductSpecification> ProductSpecifications { get; set; }
} 

public class ProductAttributeValue 
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public long ProductAttributeValueId { get; set; }

    [Required]
    public string ProductAttributeValueName { get; set; }

    public ICollection<ProductSpecification> ProductSpecifications { get; set; }
}

public class ProductSpecification
{
    public long ProductId { get; set; }
    public long ProductAttributeValueId { get; set; }

    public string Note { get; set; }

    public Product Product { get; set; }
    public ProductAttributeValue ProductAttributeValue { get; set; }
}

// Configuration in the dbConext
modelBuilder.Entity<ProductSpecification>().HasKey(ps => new { ps.ProductId, ps.ProductAttributeValueId });
modelBuilder.Entity<ProductSpecification>().HasOne(p => p.Product).WithMany(ps => ps.ProductSpecifications).HasForeignKey(ps => ps.ProductId);
modelBuilder.Entity<ProductSpecification>().HasOne(pav => pav.ProductAttributeValue).WithMany(ps => ps.ProductSpecifications).HasForeignKey(ps => ps.ProductAttributeValueId);

在控制器中：

public async Task<IActionResult> UpdateProduct([FromRoute] long id, [FromBody] Product product)
{
    if (!ModelState.IsValid)
    {
        return BadRequest(ModelState);
    }

    if (id != product.ProductId)
    {
        return BadRequest();
    }

    Product productToBeUpdated = await _unitOfWork.Repository<Product>().GetEntityList(p => p.ProductId == id).Include(p => p.ProductSpecifications).SingleOrDefaultAsync();

    if (productToBeUpdated == null)
    {
        return NotFound();
    }

    foreach (ProductSpecification productSpecification in productToBeUpdated.ProductSpecifications.ToList())
    {
        productToBeUpdated.ProductSpecifications.Remove(productSpecification);
    }

    productToBeUpdated.ProductSpecifications = product.ProductSpecifications;

    productToBeUpdated.ModifiedOn = DateTime.UtcNow;
    await _unitOfWork.SaveChangesAsync();

    return Ok(true);
 }

我也试过了：

foreach (ProductSpecification productSpecification in productToBeUpdated.ProductSpecifications.ToList())
{
    _unitOfWork.Repository<ProductSpecifications>().DeleteEntity(productSpecification);
}

他们都抛出了以下异常：

无法跟踪实体类型“ProductSpecification”的实例，因为已经在跟踪具有相同键值 {'ProductId', 'ProductAttributeValueId'} 的另一个实例。附加现有实体时，请确保仅附加一个具有给定键值的实体实例。考虑使用“DbContextOptionsBuilder.EnableSensitiveDataLogging”来查看冲突的键值。

找不到问题的真正所在！任何帮助将不胜感激！

Answer 1

问题终于确定了！在 Entity Framework 6.x 中，在多对多导航属性更新过程中，我们可以清除/删除现有的子列表，然后将新的子列表添加到父级，最后更新父级和父级使用新的子列表更新。

但在 Entity Framework Core 中，我们不能这样做。错误消息表明我们不能多次拥有具有相同键值的相同子项。我们必须在 Entity Framework 事务中保持实体的唯一性。

这就是为什么我们必须首先确定哪些现有的孩子正在被删除，哪些孩子是在更新操作期间新添加的。这将使实体框架事务状态独一无二。

所以Update方法如下：

public async Task<IActionResult> UpdateProduct([FromRoute] long id, [FromBody] Product product)
{
    if (!ModelState.IsValid)
    {
       return BadRequest(ModelState);
    }

    if (id != product.ProductId)
    {
       return BadRequest();
    }

    Product productToBeUpdated = await _unitOfWork.Repository<Product>().GetEntityList(p => p.ProductId == id).Include(p => p.ProductSpecifications).SingleOrDefaultAsync();
    if (productToBeUpdated == null)
    {
        return NotFound();
    }

    _mapper.Map(product, productToBeUpdated); // If you use AutoMapper than ignore the many-to-many navigation property in the mapping

   List<ProductSpecification> productSpecificationsToBeDeleted = productToBeUpdated.ProductSpecifications.Where(c1 => product.ProductSpecifications.All(c2 => c2.ProductAttributeValueId != c1.ProductAttributeValueId)).ToList();
   foreach (ProductSpecification productSpecification in productSpecificationsToBeDeleted)
   {
                productToBeUpdated.ProductSpecifications.Remove(productSpecification);
   }

   List<ProductSpecification> productSpecificationsToBeAdded = product.ProductSpecifications.Where(c1 => productToBeUpdated.ProductSpecifications.All(c2 => c2.ProductAttributeValueId != c1.ProductAttributeValueId)).ToList();
   foreach (ProductSpecification productSpecification in productSpecificationsToBeAdded)
   {
                productToBeUpdated.ProductSpecifications.Add(productSpecification);
   }

   productToBeUpdated.ModifiedOn = DateTime.UtcNow;
   await _unitOfWork.SaveChangesAsync();
   return Ok(true);
}