example: migration

Author: marvin-j97

Diff for: examples/migration/.run

@@ -0,0 +1,11 @@
+[package]
+name = "migration"
+version = "0.0.1"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+fjall = { path = "../../" }
+rmp-serde = "1.1.2"
+serde = { version = "1.0.193", features = ["derive"] }

Diff for: examples/migration/Cargo.toml

@@ -0,0 +1,3 @@
+# migration
+
+This example uses `fjall`, `serde` and `rmp-serde` to store and load persistent, structured data, then migrate it from one schema version to the next using `ingest`.

Diff for: examples/migration/README.md

@@ -0,0 +1,114 @@
+use fjall::Config;
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Deserialize, Serialize)]
+pub struct PlanetV1 {
+    /// ID
+    id: String,
+
+    /// Name
+    name: String,
+}
+
+#[derive(Debug, Deserialize, Serialize)]
+pub struct PlanetV2 {
+    /// ID
+    id: String,
+
+    /// Name
+    name: String,
+
+    /// Mass
+    mass: Option<u128>,
+
+    /// Radius
+    radius: Option<u128>,
+}
+
+impl From<PlanetV1> for PlanetV2 {
+    fn from(value: PlanetV1) -> Self {
+        Self {
+            id: value.id,
+            name: value.name,
+            mass: None,
+            radius: None,
+        }
+    }
+}
+
+#[derive(Debug, Deserialize, Serialize)]
+pub enum Planet {
+    V1(PlanetV1),
+    V2(PlanetV2),
+}
+
+impl std::fmt::Display for Planet {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{:?}", self)
+    }
+}
+
+fn main() -> fjall::Result<()> {
+    let path = std::path::Path::new(".fjall_data");
+
+    let keyspace = Config::new(path).temporary(true).open()?;
+    let planets_v1 = keyspace.open_partition("v1_planets", Default::default())?;
+
+    for (id, name) in [
+        ("p:earth", "Earth"),
+        ("p:jupiter", "Jupiter"),
+        ("p:neptune", "Mars"),
+        ("p:neptune", "Mercury"),
+        ("p:neptune", "Neptune"),
+        ("p:saturn", "Saturn"),
+        ("p:uranus", "Uranus"),
+        ("p:venus", "Venus"),
+    ] {
+        planets_v1.insert(
+            id,
+            rmp_serde::to_vec(&Planet::V1(PlanetV1 {
+                id: id.into(),
+                name: name.into(),
+            }))
+            .unwrap(),
+        )?;
+    }
+
+    eprintln!("--- v1 ---");
+    for kv in planets_v1.iter() {
+        let (_, v) = kv?;
+        let planet = rmp_serde::from_slice::<Planet>(&v).unwrap();
+        eprintln!("{planet:?}");
+    }
+
+    // Do migration from V1 -> V2
+    let planets_v2 = keyspace.open_partition("v2_planets", Default::default())?;
+
+    let stream = planets_v1.iter().map(|kv| {
+        let (k, v) = kv.unwrap();
+        let planet = rmp_serde::from_slice::<Planet>(&v).unwrap();
+
+        if let Planet::V1(planet) = planet {
+            let v2: PlanetV2 = planet.into();
+            let v2 = Planet::V2(v2);
+            (k, rmp_serde::to_vec(&v2).unwrap())
+        } else {
+            unreachable!("v1 does not contain other versions");
+        }
+    });
+    planets_v2.ingest(stream)?;
+
+    eprintln!("--- v2 ---");
+    for kv in planets_v2.iter() {
+        let (_, v) = kv?;
+        let planet = rmp_serde::from_slice::<Planet>(&v).unwrap();
+        eprintln!("{planet:?}");
+    }
+
+    assert_eq!(planets_v1.len()?, planets_v2.len()?);
+
+    // Delete old data
+    keyspace.delete_partition(planets_v1)?;
+
+    Ok(())
+}