How do I change Serde's default implementation

问题:

I'm developing an API wrapper and I'm having some troubles with the deserialization of an empty JSON object.

The API returns this JSON object. Mind the empty object at entities:

{
  "object": "page",
  "entry": [
    {
      "id": "1158266974317788",
      "messaging": [
        {
          "sender": {
            "id": "some_id"
          },
          "recipient": {
            "id": "some_id"
          },
          "message": {
            "mid": "mid.$cAARHhbMo8SBllWARvlfZBrJc3wnP",
            "seq": 5728,
            "text": "test",
            "nlp": {
              "entities": {} // <-- here
            }
          }
        }
      ]
    }
  ]
}

This is my equivalent struct of the message property (edited):

 #[derive(Serialize, Deserialize, Clone, Debug)]
pub struct TextMessage {
    pub mid: String,
    pub seq: u64,
    pub text: String,
    pub nlp: NLP,
}

#[derive(Serialize, Deserialize, Clone, Debug)]
pub struct NLP {
    pub entities: Intents,
}

#[derive(Serialize, Deserialize, Clone, Debug)]
pub struct Intents {
    intent: Option<Vec<Intent>>,
}

#[derive(Serialize, Deserialize, Clone, Debug)]
pub struct Intent {
    confidence: f64,
    value: String,
}

Serde's default is to deserialize Options, which are None, with ::serde_json::Value::Null.

回答1:

I solved this problem differently with no need to change the default implementation. I used serde's field attributes to skip the intent property when the Option is None. Because there is only one property in the struct Intents, this will create an empty object.

#[derive(Serialize, Deserialize, Clone, Debug)]
pub struct TextMessage {
    pub mid: String,
    pub seq: u64,
    pub text: String,
    pub nlp: NLP,
}

#[derive(Serialize, Deserialize, Clone, Debug)]
pub struct NLP {
    pub entities: Intents,
}

#[derive(Serialize, Deserialize, Clone, Debug)]
pub struct Intents {
    #[serde(skip_serializing_if="Option::is_none")]
    intent: Option<Vec<Intent>>,
}

#[derive(Serialize, Deserialize, Clone, Debug)]
pub struct Intent {
    confidence: f64,
    value: String,
}