javascript Lodash：从多个构建单个对象 - 合并/覆盖属性
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Lodash: Constructing single object from many - Merging/overriding properties
提问by Olivier Clément
Note: I filed this question under lodash as I'm pretty sure it can help me solve that problem nicely, but haven't put my finger on it just now
注意：我在 lodash 下提交了这个问题，因为我很确定它可以帮助我很好地解决这个问题，但现在还没有解决
I have an object describing different user roles and their permissions;
我有一个描述不同用户角色及其权限的对象；
I will have something like 10-15 roles defined "like this" (this doesn't reflect the application code but the problem itself):
我将“像这样”定义 10-15 个角色（这不反映应用程序代码，而是问题本身）：
var role1 = {
views: {
v1: {access: true},
v2: {access: false},
v#: {access: false}
}
}
var role2 = {
views: {
v1: {access: false},
v2: {access: true},
v3: {access: true},
}
}
The user connected will have multiple roles; In that example it could be ['role1', 'role2'], and out of this I need to construct a single permissionsobject that will be a combination of all the props defined in all the user roles.
连接的用户将有多个角色；在那个例子中，它可能是['role1', 'role2']，除此之外，我需要构造一个单一的permissions对象，它将是所有用户角色中定义的所有道具的组合。
It is basically whitelist-based, where all "true" properties should override anything that was defined as false. Thus, the expected result should be:
它基本上是基于白名单的，其中所有“true”属性都应该覆盖任何定义为 false 的属性。因此，预期的结果应该是：
permissions = {
views: {
v1: {access: true},
v2: {access: true},
v2: {access: true}
}
}
I'm not too sure how to tackle that one without relying on crazy nested loops
我不太确定如何在不依赖疯狂嵌套循环的情况下解决这个问题
Here's a starting point in JSBin: http://jsbin.com/usaQejOJ/1/edit?js,console
这是 JSBin 的起点：http://jsbin.com/usaQejOJ/1/edit?js,console
Thanks for your help!
谢谢你的帮助！
回答by adamesque
Lodash has a few methods that will help to elegantly solve this problem.
Lodash 有一些方法可以帮助优雅地解决这个问题。
First of all, the mergemethod. It takes multiple source objects, and recursively merges their properties together into a destination object. If two objects have the same property name, the latter value will override the former.
首先是merge方法。它接受多个源对象，并递归地将它们的属性合并到一个目标对象中。如果两个对象具有相同的属性名称，则后者的值将覆盖前者。
This is almost what we want; it'll merge your role objects together into a single object. What we don't want is that override behavior; we want truevalues to always override falseones. Luckily, you can pass in a custom merge function, and lodash's mergewill use that to compute the merged value when two objects have the same key.
这几乎就是我们想要的；它会将您的角色对象合并为一个对象。我们不想要的是覆盖行为；我们希望true值总是覆盖false那些。幸运的是，您可以传入一个自定义合并函数，merge当两个对象具有相同的键时，lodash将使用它来计算合并值。
We'll write a custom function to logically ORyour items together (instead of allowing later falsevalues to override trues.), so that if either value is true, the resulting merged value will be true.
我们将编写一个自定义函数，将OR您的项目逻辑上放在一起（而不是允许后面的false值覆盖trues。），以便如果任一值是true，则生成的合并值将是true。
Because our objects are nested, we'll need to make sure our custom merge function only does this ORwhen it's comparing boolean values. When comparing objects, we want to do a normal merge of their properties (again using our custom function to do the merge). It looks something like this:
因为我们的对象是嵌套的，所以我们需要确保我们的自定义合并函数只OR在比较布尔值时才这样做。比较对象时，我们希望对其属性进行正常合并（再次使用我们的自定义函数进行合并）。它看起来像这样：
function do_merge(roles) {
// Custom merge function ORs together non-object values, recursively
// calls itself on Objects.
var merger = function (a, b) {
if (_.isObject(a)) {
return _.merge({}, a, b, merger);
} else {
return a || b;
}
};
// Allow roles to be passed to _.merge as an array of arbitrary length
var args = _.flatten([{}, roles, merger]);
return _.merge.apply(_, args);
}
do_merge([role1, role2, role3]);
Lodash helps out in one other way: You may notice from the docs that _.mergedoesn't accept an array of objects to merge together; you have to pass them in as arguments. In our case, though, an array would be awfully convenient.
Lodash 以另一种方式提供帮助：您可能会从文档中注意到_.merge不接受将对象数组合并在一起；你必须将它们作为参数传递。但是，在我们的例子中，数组会非常方便。
To get around this, we'll use JavaScript's applymethod, which allows you to invoke a method by passing its arguments as an array, and Lodash's handy flattenmethod, which takes an array that might contain nested arrays — like [1, [2, 3], [4, 5]]—?and flattens it into [1, 2, 3, 4, 5].
为了解决这个问题，我们将使用 JavaScript 的apply方法，它允许您通过将其参数作为数组传递来调用方法，以及 Lodash 的方便的flatten方法，它接受一个可能包含嵌套数组的数组 - 例如[1, [2, 3], [4, 5]]-? 并将其展平为[1, 2, 3, 4, 5].
So we'll gather up all the arguments we need in a flattened array, and then applythem to merge!
因此，我们将在flattened 数组中收集我们需要的所有参数，然后将apply它们添加到merge!
If your objects are nested very very deeply, there's a chance you'll overflow the stack calling mergerrecursively like this, but for your objects this should work just fine.
如果您的对象嵌套非常深，您可能会merger像这样递归调用堆栈溢出，但是对于您的对象，这应该可以正常工作。
