实体框架核心更新多对多

Question

我们将现有的MVC6 EF6应用程序移植到Core.

EF Core中有一个简单的方法来更新多对多关系吗？

我从EF6清除列表并用新数据覆盖它的旧代码不再有效.

var model = await _db.Products.FindAsync(vm.Product.ProductId);
model.Colors.Clear();
model.Colors =  _db.Colors.Where(x => 
vm.ColorsSelected.Contains(x.ColorId)).ToList();

Answer 1

这对你有用.

创建一个类来建立关系:

public class ColorProduct
{
    public int ProductId { get; set; }
    public int ColorId { get; set; }

    public Color Color { get; set; }
    public Product Product { get; set; }
}

将一个ColorProduct集合添加到您的Product和Color类:

 public ICollection<ColorProduct> ColorProducts { get; set; }

然后使用我做的这个扩展来删除未选中的并将新选择添加到列表中:

public static void TryUpdateManyToMany<T, TKey>(this DbContext db, IEnumerable<T> currentItems, IEnumerable<T> newItems, Func<T, TKey> getKey) where T : class
{
    db.Set<T>().RemoveRange(currentItems.Except(newItems, getKey));
    db.Set<T>().AddRange(newItems.Except(currentItems, getKey));
}

public static IEnumerable<T> Except<T, TKey>(this IEnumerable<T> items, IEnumerable<T> other, Func<T, TKey> getKeyFunc)
{
    return items
        .GroupJoin(other, getKeyFunc, getKeyFunc, (item, tempItems) => new { item, tempItems })
        .SelectMany(t => t.tempItems.DefaultIfEmpty(), (t, temp) => new { t, temp })
        .Where(t => ReferenceEquals(null, t.temp) || t.temp.Equals(default(T)))
        .Select(t => t.t.item);
}

使用它看起来像这样:

var model = _db.Products
    .Include(x => x.ColorProducts)
    .FirstOrDefault(x => x.ProductId == vm.Product.ProductId);

_db.TryUpdateManyToMany(model.ColorProducts, vm.ColorsSelected
    .Select(x => new ColorProduct
    {
        ColorId = x,
        ProductId = vm.Product.ProductId
    }), x => x.ColorId);