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more clever version number handling

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xenofem 2022-08-15 17:02:33 -04:00
parent efd3124b29
commit af1f95c88b
1 changed files with 20 additions and 5 deletions
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25
src/lib.rs
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@ -47,9 +47,12 @@ pub struct JsonDb<T: Schema> {
/// other fields of the corresponding schema version; earlier versions
/// will be migrated to the current version automatically.
pub trait Schema: DeserializeOwned + Serialize {
const VERSION: u32;
/// Previous schema that can be migrated into the new schema
type Prev: Schema + Into<Self>;
/// Schema version number
const VERSION: u32 = Self::Prev::VERSION + 1;
fn parse(s: &str) -> Result<Self, Error> {
let Version { version } = serde_json::from_str(s)?;
match version.cmp(&Self::VERSION) {
@ -64,11 +67,25 @@ pub trait Schema: DeserializeOwned + Serialize {
///
/// Implementing this will automatically implement [`Schema`], with
/// version number `0` and `Self` as the previous version.
pub trait SchemaV0: DeserializeOwned + Serialize {}
pub trait SchemaV0: DeserializeOwned + Serialize {
/// Set this to false if your version 0 is a pre-`JsonDb` schema
/// that does not include a version number.
const EXPECT_VERSION_NUMBER: bool = true;
}
impl<T: SchemaV0> Schema for T {
const VERSION: u32 = 0;
type Prev = Self;
const VERSION: u32 = 0;
fn parse(s: &str) -> Result<Self, Error> {
if Self::EXPECT_VERSION_NUMBER {
let Version { version } = serde_json::from_str(s)?;
if version != 0 {
return Err(Error::UnknownVersion(version));
}
}
Ok(serde_json::from_str(s)?)
}
}
#[derive(Deserialize)]
@ -216,7 +233,6 @@ mod tests {
last_updated: i64,
}
impl Schema for V1 {
const VERSION: u32 = 1;
type Prev = V0;
}
impl From<V0> for V1 {
@ -248,7 +264,6 @@ mod tests {
}
}
impl Schema for V2 {
const VERSION: u32 = 2;
type Prev = V1;
}
impl From<V1> for V2 {