batch abstraction for migration

util/src/migration/mod.rs

@@ -39,6 +39,45 @@ impl Default for Config {
 	}
 }
 
+/// A batch of key-value pairs to be written into the database.
+pub struct Batch {
+	inner: BTreeMap<Vec<u8>, Vec<u8>>,
+	batch_size: usize,
+}
+
+impl Batch {
+	/// Make a new batch with the given config.
+	pub fn new(config: &Config) -> Self {
+		Batch {
+			inner: BTreeMap::new(),
+			batch_size: config.batch_size,
+		}
+	}
+
+	/// Insert a value into the batch, committing if necessary.
+	pub fn insert(&mut self, key: Vec<u8>, value: Vec<u8>, dest: &mut Database) -> Result<(), Error> {
+		self.inner.insert(key, value);
+		if self.inner.len() == self.batch_size {
+			try!(self.commit(dest));
+		}
+		Ok(())
+	}
+
+	/// Commit all the items in the batch to the given database.
+	pub fn commit(&mut self, dest: &mut Database) -> Result<(), Error> {
+		if self.inner.is_empty() { return Ok(()) }
+
+		let transaction = DBTransaction::new();
+
+		for keypair in &self.inner {
+			try!(transaction.put(&keypair.0, &keypair.1).map_err(Error::Custom));
+		}
+
+		self.inner.clear();
+		dest.write(transaction).map_err(Error::Custom)
+	}
+}
+
 /// Migration error.
 #[derive(Debug)]
 pub enum Error {
@@ -79,39 +118,18 @@ impl<T: SimpleMigration> Migration for T {
 	fn version(&self) -> u32 { SimpleMigration::version(self) }
 
 	fn migrate(&mut self, source: &Database, config: &Config, dest: &mut Database) -> Result<(), Error> {
-		let mut batch: BTreeMap<Vec<u8>, Vec<u8>> = BTreeMap::new();
+		let mut batch = Batch::new(config);
 
 		for (key, value) in source.iter() {
-
 			if let Some((key, value)) = self.simple_migrate(key.to_vec(), value.to_vec()) {
-				batch.insert(key, value);
-			}
-
-			if batch.len() == config.batch_size {
-				try!(commit_batch(dest, &batch));
-				batch.clear();
+				try!(batch.insert(key, value, dest));
 			}
 		}
 
-		if batch.len() != 0 {
-			try!(commit_batch(dest, &batch));
-		}
-
-		Ok(())
+		batch.commit(dest)
 	}
 }
 
-/// Commit a batch of writes to a database.
-pub fn commit_batch(db: &mut Database, batch: &BTreeMap<Vec<u8>, Vec<u8>>) -> Result<(), Error> {
-	let transaction = DBTransaction::new();
-
-	for keypair in batch {
-		try!(transaction.put(&keypair.0, &keypair.1).map_err(Error::Custom));
-	}
-
-	db.write(transaction).map_err(Error::Custom)
-}
-
 /// Get the path where all databases reside.
 fn database_path(path: &Path) -> PathBuf {
 	let mut temp_path = path.to_owned();