pub fn diff<T: Serialize>(old: &T, new: &T) -> Result<Value, Error>Expand description
Computes a JSON diff suitable for use as a Merge Patch (RFC 7396).
Returns a serde_json::Value containing only changed fields (with new values).
If no changes, returns an empty object.
See also diff_including for a version that can force inclusion of specific fields.
§Example
use serde_json::json;
#[derive(serde::Serialize)]
struct User { id: u32, name: String, age: u8 }
let old = User { id: 1, name: "old".to_string(), age: 31 };
let new = User { id: 1, name: "new".to_string(), age: 31 };
let patch = serde_patch::diff(&old, &new).unwrap();
assert_eq!(patch, json!({ "name": "new" }));Examples found in repository?
examples/full.rs (line 42)
18fn main() -> Result<(), Box<dyn std::error::Error>> {
19 let old = User {
20 id: 1001,
21 username: "alice".to_string(),
22 age: 30,
23 active: true,
24 profile: Some(Profile {
25 bio: "Software engineer".to_string(),
26 avatar_url: Some("https://example.com/alice-old.jpg".to_string()),
27 }),
28 };
29
30 let new = User {
31 id: 1001,
32 username: "alice".to_string(),
33 age: 31,
34 active: false,
35 profile: Some(Profile {
36 bio: "Senior software engineer".to_string(),
37 avatar_url: None,
38 }),
39 };
40
41 // Basic diff – only changed fields
42 let basic_patch = serde_json::to_string(&serde_patch::diff(&old, &new)?)?;
43 println!("Basic patch (no forced fields):\n{}", basic_patch);
44
45 // Diff with forced field – includes "id" even though unchanged
46 let forced_patch = serde_json::to_string(&serde_patch::diff_including(&old, &new, &["id"])?)?;
47 println!("\nPatch with forced \"id\":\n{}", forced_patch);
48
49 // Apply immutably
50 let updated = serde_patch::apply(old.clone(), &basic_patch)?;
51 println!("\nImmutable apply result:\n{:#?}", updated);
52
53 // Apply mutably
54 let mut current = old;
55 serde_patch::apply_mut(&mut current, &forced_patch)?;
56 println!("\nMutable apply result:\n{:#?}", current);
57
58 assert_eq!(updated, new);
59 assert_eq!(current, new);
60
61 Ok(())
62}