Question

我们正在将现有的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？

我的旧代码来自EF6，我们清除列表并用新数据覆盖它不再有效。

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。

让课程建立关系：

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

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

在ColorProduct和Product课程中添加Color集合：

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

然后使用我所做的这个扩展来删除未选中的并将新选择的内容添加到列表中：

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);

Answer 2

为了避免在上述答案中出现LINQ地狱，可以将模板化的“ Except”方法重写为：

public static IEnumerable<TEntity> LeftComplementRight<TEntity, TKey>(
        this IEnumerable<TEntity> left,
        IEnumerable<TEntity> right,
        Func<TEntity, TKey> keyRetrievalFunction)
    {
        var leftSet = left.ToList();
        var rightSet = right.ToList();

        var leftSetKeys = leftSet.Select(keyRetrievalFunction);
        var rightSetKeys = rightSet.Select(keyRetrievalFunction);

        var deltaKeys = leftSetKeys.Except(rightSetKeys);
        var leftComplementRightSet = leftSet.Where(i => deltaKeys.Contains(keyRetrievalFunction.Invoke(i)));
        return leftComplementRightSet;
    }

此外，可以将UpdateManyToMany方法更新为包含已这样修改的实体：

public void UpdateManyToMany<TDependentEntity, TKey>(
        IEnumerable<TDependentEntity> dbEntries,
        IEnumerable<TDependentEntity> updatedEntries,
        Func<TDependentEntity, TKey> keyRetrievalFunction)
        where TDependentEntity : class
    {
        var oldItems = dbEntries.ToList();
        var newItems = updatedEntries.ToList();
        var toBeRemoved = oldItems.LeftComplementRight(newItems, keyRetrievalFunction);
        var toBeAdded = newItems.LeftComplementRight(oldItems, keyRetrievalFunction);
        var toBeUpdated = oldItems.Intersect(newItems, keyRetrievalFunction);

        this.Context.Set<TDependentEntity>().RemoveRange(toBeRemoved);
        this.Context.Set<TDependentEntity>().AddRange(toBeAdded);
        foreach (var entity in toBeUpdated)
        {
            var changed = newItems.Single(i => keyRetrievalFunction.Invoke(i).Equals(keyRetrievalFunction.Invoke(entity)));
            this.Context.Entry(entity).CurrentValues.SetValues(changed);
        }
    }

使用另一个自定义模板化的“相交”函数来查找两个集合的相交：

public static IEnumerable<TEntity> Intersect<TEntity, TKey>(
        this IEnumerable<TEntity> left,
        IEnumerable<TEntity> right,
        Func<TEntity, TKey> keyRetrievalFunction)
    {
        var leftSet = left.ToList();
        var rightSet = right.ToList();

        var leftSetKeys = leftSet.Select(keyRetrievalFunction);
        var rightSetKeys = rightSet.Select(keyRetrievalFunction);

        var intersectKeys = leftSetKeys.Intersect(rightSetKeys);
        var intersectionEntities = leftSet.Where(i => intersectKeys.Contains(keyRetrievalFunction.Invoke(i)));
        return intersectionEntities;
    }

实体框架核心更新多对多

2 个答案: