How do I avoid generating JSON when serializing a value that is null or a default value?

Question

The serde_json::to_string() function will generate a string which may include null for an Option<T>, or 0 for a u32. This makes the output larger, so I want to ignore these sorts of values.

I want to simplify the JSON string output of the following structure:

use serde_derive::Serialize; // 1.0.82

#[derive(Serialize)]
pub struct WeightWithOptionGroup {
    pub group: Option<String>,
    pub proportion: u32,
}

When group is None and proportion is 0, the JSON string should be "{}"

Thanks for the answerHow do I change Serde's default implementation to return an empty object instead of null?, it can resolve Optionproblem, but for 0 there is none solution.

Answer 1

The link Skip serializing field give me the answer.

And the fixed code:

#[derive(Debug, Clone, Serialize, Deserialize, Default, PartialEq, Ord, PartialOrd, Eq)]
pub struct WeightWithOptionGroup {
    #[serde(skip_serializing_if = "Option::is_none")]
    #[serde(default)]
    pub group: Option<String>,
    #[serde(skip_serializing_if = "is_zero")]
    #[serde(default)]
    pub proportion: u32,
}

/// This is only used for serialize
#[allow(clippy::trivially_copy_pass_by_ref)]
fn is_zero(num: &u32) -> bool {
    *num == 0
}

Answer 2

There's a couple of ways you could do this:

• Mark each of the fields with a skip_serialising_if attribute to say when to skip them. This is much easier, but you'll have to remember to do it for every field.
• Write your own Serde serialiser that does this custom JSON form. This is more work, but shouldn't be too bad, especially given you can still use the stock JSON deserialiser.