From af1f95c88bcc5dbbab2ab2867f7e8d4a36df151b Mon Sep 17 00:00:00 2001
From: xenofem <xenofem@xeno.science>
Date: Mon, 15 Aug 2022 17:02:33 -0400
Subject: [PATCH 1/2] more clever version number handling

---
 src/lib.rs | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index f8dd7ad..af5e749 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -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 {

From cd0a92fe94b05fe94455e0eae1ea849457cbd6de Mon Sep 17 00:00:00 2001
From: xenofem <xenofem@xeno.science>
Date: Mon, 15 Aug 2022 17:02:54 -0400
Subject: [PATCH 2/2] v0.1.1

---
 Cargo.toml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Cargo.toml b/Cargo.toml
index ea1dbe1..848bc3b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "jsondb"
-version = "0.1.0"
+version = "0.1.1"
 edition = "2021"
 authors = ["xenofem <xenofem@xeno.science>"]