c# - 是否可以根据条件在 .Select 语句中取消选择和“继续”？

Question

是否可以在 LINQ 中的 .Select 方法中跳过选择，例如 fore..each 中的“继续”？

var myFoos = allFoos.Select (foo =>                                                                                                 {

    var platform = LoadPlatform(foo);
        if (platform == "BadPlatform") // TODO:  should skip and continue
        var owner = LoadOwner(foo);
        // .... Som eother loads
});

Answer 1

您应该使用 aWhere过滤掉不需要的元素。这对于您当前的代码是不可能的，但是有很大的重构空间。像这样重写它：

var myFoos = allFoos
    .Where(foo => LoadPlatform(foo) != "BadPlatform")
    .Select(LoadOwner)
    // ...continue with your other code

如果“其他代码”也需要平台值，那么您应该首先投影到匿名类型：

var myFoos = allFoos
    .Select(foo => new { Platform = LoadPlatform(foo), Foo = foo })
    .Where(o => o.Platform != "BadPlatform")
    .Select(o => new { Platform = o.Platform, Owner = LoadOwner(o.Foo), ... })
    // ...continue with your other code

一般来说，如果可能的话，你应该避免在这种 lambdas 中编写块表达式；块表达式会导致无法轻松组合的僵化代码。

Answer 2

var myFoos = from foo in allFoos
             let platform = LoadPlatform(foo)
             where platform != "BadPlatform"
             select LoadOwner(foo);

Answer 3

你可以这样做：

var myFoos = allFoos
        .Select (foo => new {Platform = LoadPlatform(foo), Foo = foo})
        .Where(all => all.Platform != "BadPlatform")
        .Select(all => {
            var platform = all.Platform;//Not "BadPlatform"
            var owner = LoadOwner(all.Foo);
            // .... Som eother loads
        });