如何解组嵌套的未知字段

Question

我 fork 了一个很棒的项目 here，并且刚刚在学习一些围棋时遇到了麻烦。我无法弄清楚的问题是关于自定义解组的一些事情，如果你看到here，你可以看到这个解组 Thing 结构，其中包含一个 Data interface{} 字段，然后使用 Kind string 字段解组。除了嵌套情况外，这一切都很好。所以最好的就是一个例子：

只要说你有Thing 结构，它是一个listing，因此Thing.Data 被解组为类型listing。然后 listing 有 3 个 Children 类型 link 保存在 Children []Thing 字段中。这些孩子最终属于map[string]interface {} 类型，这是我的问题。我怎样才能通过嵌套数据进行解组？这样Children.Data 也被解组。有没有办法在 go 中做到这一点，还是我必须编写一个大循环或递归算法？请让我知道您的想法，或者我是否认为这种情况完全错误。谢谢

更新 这是一个json示例

{
    "kind": "Listing",
    "data": {
        "after": null,
        "dist": 10,
        "facets": {},
        "modhash": null,
        "whitelist_status": "all_ads",
        "children": [
            {
                "kind": "t3",
                "data": {
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                            "selftext_html": "<!-- SC_OFF --><div class=\"md\"><p>Seeing lots of comments about the lack of timestamps in the protocol, and just wanted to provide some information on why objectively accurate, global time timestamps are an illusion in decentralized systems. Logical time on the other hand is achievable and is in fact achieved in Nano via the individual block chains and the directed, acyclic graph (DAG). </p>\n\n<p>Generally, in a decentralized, distributed system, only logical time (C happened after B happened after A) can be agreed on globally (e.g. Lamport time: <a href=\"https://amturing.acm.org/p558-lamport.pdf\">https://amturing.acm.org/p558-lamport.pdf</a> or vector clocks). This is what the nano ledger does via chaining blocks, just as any other blockchain. Then it connects those chains via a DAG. Syncing global time to logical time is a hard problem that can either be approached via a consensus approach which is prone to sybil attacks, via a probabilistic approach which is what most blockchains go with - essentially relying on their peers - or a centralized approach like NTP which is a no-go in a decentralized system. If you're interested, check e.g. this paper: <a href=\"http://soft.vub.ac.be/%7Etvcutsem/distsys/clocks.pdf\">http://soft.vub.ac.be/~tvcutsem/distsys/clocks.pdf</a></p>\n\n<p>So what you're running into is the problem that while theoretically all or a relevant subset of nodes within the Nano or Bitcoin or Ethereum network could agree to call a certain time "Monday February 12 2018 20:35:23", this timestamp could still be incorrect vs the outside world.</p>\n\n<p>That's why any accurate global timestamps in software today rely on centralized information and trusted entities. The only way this can change is if machines start setting their clocks on their own accurately (e.g. chip-scale atomic clocks)</p>\n\n<p>Some people think this is bad news for Nano because in traditional blockchain, timestamps are fairly important because they are used in new block validation: <a href=\"http://culubas.blogspot.co.uk/2011/05/timejacking-bitcoin_802.html\">http://culubas.blogspot.co.uk/2011/05/timejacking-bitcoin_802.html</a> . Timestamps are a blessing and a curse at the same time in blockchain: They allow for timing and validation of blocks and therefore regulation of coin mining, but also allow for timestamp double spend attacks. Since Nano does not use mining, it is not susceptible to those attacks.</p>\n\n<p>Even with the relative importance of time and timestamps in Bitcoin, timestamp in Bitcoin are not guaranteed to be corresponding to logical time on the chain. Here's the bitcoin wiki talking about the bitcoin block timestamp: <a href=\"https://en.bitcoin.it/wiki/Block_timestamp\">https://en.bitcoin.it/wiki/Block_timestamp</a> </p>\n\n<blockquote>\n<p>A timestamp is accepted as valid if it is greater than the median timestamp of previous 11 blocks, and less than the network-adjusted time + 2 hours. "Network-adjusted time" is the median of the timestamps returned by all nodes connected to you. As a result, block timestamps are not exactly accurate, and they do not even need to be in order. Block times are accurate only to within an hour or two. </p>\n</blockquote>\n\n<p>This is probably as good as it gets. Still no ordering guarantees though, and a possibilities for attacks which have been discussed again and again. There are certain guards in Bitcoin code to prevent these from happening. </p>\n\n<p>So if you have somebody lecturing you about how architecturally superior coins would have a accurate and monotonically increasing timestamps, point them here, or here: <a href=\"https://cointelegraph.com/news/timestamp-hacking-debunking-the-myth-of-precision-timestamps\">https://cointelegraph.com/news/timestamp-hacking-debunking-the-myth-of-precision-timestamps</a></p>\n\n<p>Would timestamps be convenient to have on the protocol? Yes, and that would likely be a good reason to include them. Are timestamps accurately depicting global time, and can they be used as evidence in any chain? No they can't.</p>\n\n<p>Why are we seeing inaccurate timestamps in the block explorer? Because these are kept in a db outside of the ledger and have been set January 19. Nothing more to it.</p>\n\n<p>Why do people like to babble about how this is a weakness in Nano? No clue.</p>\n</div><!-- SC_ON -->",
                            "selftext": "Seeing lots of comments about the lack of timestamps in the protocol, and just wanted to provide some information on why objectively accurate, global time timestamps are an illusion in decentralized systems. Logical time on the other hand is achievable and is in fact achieved in Nano via the individual block chains and the directed, acyclic graph (DAG). \n\nGenerally, in a decentralized, distributed system, only logical time (C happened after B happened after A) can be agreed on globally (e.g. Lamport time: https://amturing.acm.org/p558-lamport.pdf or vector clocks). This is what the nano ledger does via chaining blocks, just as any other blockchain. Then it connects those chains via a DAG. Syncing global time to logical time is a hard problem that can either be approached via a consensus approach which is prone to sybil attacks, via a probabilistic approach which is what most blockchains go with - essentially relying on their peers - or a centralized approach like NTP which is a no-go in a decentralized system. If you're interested, check e.g. this paper: http://soft.vub.ac.be/~tvcutsem/distsys/clocks.pdf\n\nSo what you're running into is the problem that while theoretically all or a relevant subset of nodes within the Nano or Bitcoin or Ethereum network could agree to call a certain time \"Monday February 12 2018 20:35:23\", this timestamp could still be incorrect vs the outside world.\n\nThat's why any accurate global timestamps in software today rely on centralized information and trusted entities. The only way this can change is if machines start setting their clocks on their own accurately (e.g. chip-scale atomic clocks)\n\nSome people think this is bad news for Nano because in traditional blockchain, timestamps are fairly important because they are used in new block validation: http://culubas.blogspot.co.uk/2011/05/timejacking-bitcoin_802.html . Timestamps are a blessing and a curse at the same time in blockchain: They allow for timing and validation of blocks and therefore regulation of coin mining, but also allow for timestamp double spend attacks. Since Nano does not use mining, it is not susceptible to those attacks.\n\nEven with the relative importance of time and timestamps in Bitcoin, timestamp in Bitcoin are not guaranteed to be corresponding to logical time on the chain. Here's the bitcoin wiki talking about the bitcoin block timestamp: https://en.bitcoin.it/wiki/Block_timestamp \n\n> A timestamp is accepted as valid if it is greater than the median timestamp of previous 11 blocks, and less than the network-adjusted time + 2 hours. \"Network-adjusted time\" is the median of the timestamps returned by all nodes connected to you. As a result, block timestamps are not exactly accurate, and they do not even need to be in order. Block times are accurate only to within an hour or two. \n\nThis is probably as good as it gets. Still no ordering guarantees though, and a possibilities for attacks which have been discussed again and again. There are certain guards in Bitcoin code to prevent these from happening. \n\nSo if you have somebody lecturing you about how architecturally superior coins would have a accurate and monotonically increasing timestamps, point them here, or here: https://cointelegraph.com/news/timestamp-hacking-debunking-the-myth-of-precision-timestamps\n\nWould timestamps be convenient to have on the protocol? Yes, and that would likely be a good reason to include them. Are timestamps accurately depicting global time, and can they be used as evidence in any chain? No they can't.\n\nWhy are we seeing inaccurate timestamps in the block explorer? Because these are kept in a db outside of the ledger and have been set January 19. Nothing more to it.\n\nWhy do people like to babble about how this is a weakness in Nano? No clue.",
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Answer 1

这正是json.RawMessage 的用途（查看文档中的解组示例）。首先解组 JSON 对象的顶层，检查 kind 字段，然后解组 data 字段：

type Listing struct {                                           
    WhitelistStatus string  `json:"whitelist_status"`           
    Children        []Thing `json:"children"`                   
}                                                               

type T3 struct {                                                
    Domain              string `json:"domain"`                  
    CrosspostParentList []struct {                              
            Domain string `json:"domain"`                       
    } `json:"crosspost_parent_list"`                            
}                                                               

type Thing struct {
    Kind string      `json:"kind"`
    Data interface{} `json:"data"`
}

func (t *Thing) UnmarshalJSON(b []byte) error {
    var step1 struct {
            Kind string          `json:"kind"`
            Data json.RawMessage `json:"data"` 
    }

    if err := json.Unmarshal(b, &step1); err != nil {
            return err
    }

    var step2 interface{}
    switch step1.Kind {
    case "Listing":
            step2 = &Listing{}
    case "t3":
            step2 = &T3{}
    default:
            return errors.New("unknown kind: " + step1.Kind) // or simply ignore
    }

    if err := json.Unmarshal(b, step2); err != nil {
            return err
    }

    t.Kind = step1.Kind
    t.Data = step2

    return nil
}

在操场上试试看：https://play.golang.org/p/giBVT2IWPd-

Answer 2

在您的情况下，您需要创建一个递归函数，它将获取底层 interface{} 的嵌套值直到最后一个深度。我们无法从 interface{} 获取具有未知底层类型的嵌套值。这是您可以在代码中执行的操作的example