Add JSON versioning docs + examples

src/storage/codec_json.rs

@@ -21,6 +21,98 @@ use super::Codec;
 /// #    view! { }
 /// # }
 /// ```
+///
+/// ## Versioning
+///
+/// If the JSON decoder fails, the storage hook will return `T::Default` dropping the stored JSON value. See [`Codec`](super::Codec) for general information on codec versioning.
+///
+/// ### Rely on serde
+/// This codec uses [`serde_json`] under the hood. A simple way to avoid complex versioning is to rely on serde's [field attributes](https://serde.rs/field-attrs.html) such as [`serde(default)`](https://serde.rs/field-attrs.html#default) and [`serde(rename = "...")`](https://serde.rs/field-attrs.html#rename).
+///
+/// ### String replacement
+/// Previous versions of leptos-use offered a `merge_defaults` fn to rewrite the encoded value. This is possible by wrapping the codec but should be avoided.
+///
+/// ```
+/// # use leptos::*;
+/// # use leptos_use::storage::{StorageType, use_local_storage, use_session_storage, use_storage_with_options, UseStorageOptions, Codec, JsonCodec};
+/// # use serde::{Deserialize, Serialize};
+/// #
+/// # pub fn Demo() -> impl IntoView {
+/// #[derive(Serialize, Deserialize, Clone, Default, PartialEq)]
+/// pub struct MyState {
+///     pub hello: String,
+///     pub greeting: String,
+/// }
+///
+/// #[derive(Clone, Default)]
+/// pub struct MyStateCodec();
+/// impl Codec<MyState> for MyStateCodec {
+///     type Error = serde_json::Error;
+///
+///     fn encode(&self, val: &MyState) -> Result<String, Self::Error> {
+///         serde_json::to_string(val)
+///     }
+///
+///     fn decode(&self, stored_value: String) -> Result<MyState, Self::Error> {
+///         let default_value = MyState::default();
+///         let rewritten = if stored_value.contains(r#""greeting":"#) {
+///             stored_value
+///         } else {
+///             // add "greeting": "Hello" to the string
+///             stored_value.replace("}", &format!(r#""greeting": "{}"}}"#, default_value.greeting))
+///         };
+///         serde_json::from_str(&rewritten)
+///     }
+/// }
+///
+/// let (get, set, remove) = use_local_storage::<MyState, MyStateCodec>("my-struct-key");
+/// #    view! { }
+/// # }
+/// ```
+///
+/// ### Transform a `JsValue`
+/// A better alternative to string replacement might be to parse the JSON then transform the resulting `JsValue` before decoding it to to your struct again.
+///
+/// ```
+/// # use leptos::*;
+/// # use leptos_use::storage::{StorageType, use_local_storage, use_session_storage, use_storage_with_options, UseStorageOptions, Codec, JsonCodec};
+/// # use serde::{Deserialize, Serialize};
+/// # use serde_json::json;
+/// #
+/// # pub fn Demo() -> impl IntoView {
+/// #[derive(Serialize, Deserialize, Clone, Default, PartialEq)]
+/// pub struct MyState {
+///     pub hello: String,
+///     pub greeting: String,
+/// }
+///
+/// #[derive(Clone, Default)]
+/// pub struct MyStateCodec();
+/// impl Codec<MyState> for MyStateCodec {
+///     type Error = serde_json::Error;
+///
+///     fn encode(&self, val: &MyState) -> Result<String, Self::Error> {
+///         serde_json::to_string(val)
+///     }
+///
+///     fn decode(&self, stored_value: String) -> Result<MyState, Self::Error> {
+///         let mut val: serde_json::Value = serde_json::from_str(&stored_value)?;
+///         // add "greeting": "Hello" to the object if it's missing
+///         if let Some(obj) = val.as_object_mut() {
+///             if !obj.contains_key("greeting") {
+///                obj.insert("greeting".to_string(), json!("Hello"));
+///             }
+///             serde_json::from_value(val)
+///         } else {
+///             Ok(MyState::default())
+///         }
+///     }
+/// }
+///
+/// let (get, set, remove) = use_local_storage::<MyState, MyStateCodec>("my-struct-key");
+/// #    view! { }
+/// # }
+/// ```
 #[derive(Clone, Default, PartialEq)]
 pub struct JsonCodec();