Question

我有一个方法，它使用大量LINQ来设置和匹配Tuple<string, int>列表中的某些值。

现在我仍然坚持使用两个相互嵌套的foreach循环，我认为可以将它们组合成一个巨大的LINQ查询。我想知道在优化过程中最好的方法是什么。

这是我正在谈论的功能：

private async void AddLocalChangesFromPendingOperations()
{
    var pendingOperations = await this.operationsStorage.GetOperationsAsync();
    var list = pendingOperations.
        SelectMany(pendingOperation =>
                           pendingOperation.Settings, (pendingOperation, setting) =>
                           new { pendingOperation, setting })
        .Where(a => a.setting.Key == "selection")
        .Select(a => new Tuple<string, int>(
                                             a.pendingOperation.DefinitionId,
                                             Convert.ToInt32(a.setting.Value.ValueObject)))
        .ToList();

    foreach (var pendingChange in list)
    {
        var selection = await this.selectionsStorage.GetSelectionByIdAsync(pendingChange.Item2);
        foreach (var selectionsViewModel in this.SelectionsList.Where(a => a.Name == selection.Name))
        {
            if (pendingChange.Item1 == "selection-add-animals")
            {
                selectionsViewModel.IsActive = true;
            }
            else if (pendingChange.Item1 == "selection-remove-animals")
            {
                selectionsViewModel.IsActive = false;
            }
        }
    }
}

如果可能的话，我想在使用linq时优化最后两个foreach。我已经尝试了一些东西，但我仍坚持在当前列表中设置值...

我这样做：

this.SelectionsList = this
    .SelectionsList
    .Where(a => a.Name == selection.Name)
    .SingleOrDefault(
        a => pendingChange.Item1 == "selection-add-animals" ? a.IsActive = true : a.IsActive = false
    );

Answer 1

您可以执行以下操作：

this.SelectionsList = this.SelectionsList
    .Where(a => a.Name == selection.Name)
    .Select(a => 
    {
        a.IsActive = a.Name == selection.Name ? true:false;
        return a;
    }).ToList();

Answer 2

通常，LINQ用于查询项目（语言集成Query）。然而，你可以进行查询，然后在最后做一个foreach：

private async void AddLocalChangesFromPendingOperations()
{
    var pendingOperations = await this.operationsStorage.GetOperationsAsync();

    (await Task.WhenAll(pendingOperations
        .SelectMany(pendingOperation =>
                           pendingOperation.Settings, (pendingOperation, setting) =>
                           new { pendingOperation, setting })
        .Where(a => a.setting.Key == "selection")
        .Select(a => Tuple.Create(a.pendingOperation.DefinitionId, Convert.ToInt32(a.setting.Value.ValueObject)))
        .Select(async pendingChange => Tuple.Create(await this.selectionsStorage.GetSelectionByIdAsync(pendingChange.Item2)), pendingChange))
        .SelectMany(tuple => this.SelectionsList.Where(a => a.Name == tuple.Item1.Name)
                                                .Select(selectionsViewModel => Tuple.Create(selectionsViewModel, tuple.Item2))
        .Select(tuple => Tuple.Create(tuple.Item1, tuple.Item2.Item1 == "selection-add-animals"))
        .ToList()
        .ForEach(tuple => tuple.Item1.IsActive = tuple.Item2);
}

这是否比原始实现更清晰可供讨论（我不认为），但这是一种方法。

注意：这是直接在编辑器中输入的，可能会有一些小的语法错误。

Linq将两个陈述合并为一个大的陈述（优化）

2 个答案: