Skip serializing field

NOTE: Using skip_serializing does not skip deserializing the field. If you only add the skip_serializing attribute, and then attempt to deserialize the data, it will fail, as it will still attempt to deserialize the skipped field. Please use the skip attribute to skip both serializing and deserializing (see Field Attributes: skip). Likewise, use skip_deserializing to skip deserializing only.

#[macro_use]
extern crate serde_derive;

extern crate serde;
extern crate serde_json;

use std::collections::BTreeMap as Map;

#[derive(Serialize)]
struct Resource {
    // Always serialized.
    name: String,

    // Never serialized.
    #[serde(skip_serializing)]
    hash: String,

    // Use a method to decide whether the field should be skipped.
    #[serde(skip_serializing_if = "Map::is_empty")]
    metadata: Map<String, String>,
}

fn main() {
    let resources = vec![
        Resource {
            name: "Stack Overflow".to_string(),
            hash: "b6469c3f31653d281bbbfa6f94d60fea130abe38".to_string(),
            metadata: Map::new(),
        },
        Resource {
            name: "GitHub".to_string(),
            hash: "5cb7a0c47e53854cd00e1a968de5abce1c124601".to_string(),
            metadata: {
                let mut metadata = Map::new();
                metadata.insert("headquarters".to_string(),
                                "San Francisco".to_string());
                metadata
            },
        },
    ];

    let json = serde_json::to_string_pretty(&resources).unwrap();

    // Prints:
    //
    //    [
    //      {
    //        "name": "Stack Overflow"
    //      },
    //      {
    //        "name": "GitHub",
    //        "metadata": {
    //          "headquarters": "San Francisco"
    //        }
    //      }
    //    ]
    println!("{}", json);
}