src/db/lib.rs

@@ -211,12 +211,16 @@ impl Tree {
 
 	/// Returns the old value if there was one
 	#[inline]
-	pub fn insert<T: AsRef<[u8]>, U: AsRef<[u8]>>(&self, key: T, value: U) -> Result<()> {
+	pub fn insert<T: AsRef<[u8]>, U: AsRef<[u8]>>(
+		&self,
+		key: T,
+		value: U,
+	) -> Result<Option<Value>> {
 		self.0.insert(self.1, key.as_ref(), value.as_ref())
 	}
 	/// Returns the old value if there was one
 	#[inline]
-	pub fn remove<T: AsRef<[u8]>>(&self, key: T) -> Result<()> {
+	pub fn remove<T: AsRef<[u8]>>(&self, key: T) -> Result<Option<Value>> {
 		self.0.remove(self.1, key.as_ref())
 	}
 	/// Clears all values from the tree
@@ -335,8 +339,8 @@ pub(crate) trait IDb: Send + Sync {
 	fn get(&self, tree: usize, key: &[u8]) -> Result<Option<Value>>;
 	fn len(&self, tree: usize) -> Result<usize>;
 
-	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<()>;
-	fn remove(&self, tree: usize, key: &[u8]) -> Result<()>;
+	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<Option<Value>>;
+	fn remove(&self, tree: usize, key: &[u8]) -> Result<Option<Value>>;
 	fn clear(&self, tree: usize) -> Result<()>;
 
 	fn iter(&self, tree: usize) -> Result<ValueIter<'_>>;

src/db/lmdb_adapter.rs

@@ -132,20 +132,22 @@ impl IDb for LmdbDb {
 		Ok(tree.len(&tx)?.try_into().unwrap())
 	}
 
-	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<()> {
+	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<Option<Value>> {
 		let tree = self.get_tree(tree)?;
 		let mut tx = self.db.write_txn()?;
+		let old_val = tree.get(&tx, key)?.map(Vec::from);
 		tree.put(&mut tx, key, value)?;
 		tx.commit()?;
-		Ok(())
+		Ok(old_val)
 	}
 
-	fn remove(&self, tree: usize, key: &[u8]) -> Result<()> {
+	fn remove(&self, tree: usize, key: &[u8]) -> Result<Option<Value>> {
 		let tree = self.get_tree(tree)?;
 		let mut tx = self.db.write_txn()?;
+		let old_val = tree.get(&tx, key)?.map(Vec::from);
 		tree.delete(&mut tx, key)?;
 		tx.commit()?;
-		Ok(())
+		Ok(old_val)
 	}
 
 	fn clear(&self, tree: usize) -> Result<()> {

src/db/sqlite_adapter.rs

@@ -169,7 +169,7 @@ impl IDb for SqliteDb {
 		}
 	}
 
-	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<()> {
+	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<Option<Value>> {
 		let tree = self.get_tree(tree)?;
 		let db = self.db.get()?;
 		let lock = self.write_lock.lock();
@@ -184,18 +184,23 @@ impl IDb for SqliteDb {
 		assert_eq!(n, 1);
 
 		drop(lock);
-		Ok(())
+		Ok(old_val)
 	}
 
-	fn remove(&self, tree: usize, key: &[u8]) -> Result<()> {
+	fn remove(&self, tree: usize, key: &[u8]) -> Result<Option<Value>> {
 		let tree = self.get_tree(tree)?;
 		let db = self.db.get()?;
 		let lock = self.write_lock.lock();
 
-		let n = db.execute(&format!("DELETE FROM {} WHERE k = ?1", tree), params![key])?;
+		let old_val = self.internal_get(&db, &tree, key)?;
+
+		if old_val.is_some() {
+			let n = db.execute(&format!("DELETE FROM {} WHERE k = ?1", tree), params![key])?;
+			assert_eq!(n, 1);
+		}
 
 		drop(lock);
-		Ok(())
+		Ok(old_val)
 	}
 
 	fn clear(&self, tree: usize) -> Result<()> {

src/db/test.rs

@@ -12,7 +12,7 @@ fn test_suite(db: Db) {
 
 	// ---- test simple insert/delete ----
 
-	assert!(tree.insert(ka, va).is_ok());
+	assert!(tree.insert(ka, va).unwrap().is_none());
 	assert_eq!(tree.get(ka).unwrap().unwrap(), va);
 	assert_eq!(tree.len().unwrap(), 1);
 
@@ -50,7 +50,7 @@ fn test_suite(db: Db) {
 	assert!(iter.next().is_none());
 	drop(iter);
 
-	assert!(tree.insert(kb, vc).is_ok());
+	assert!(tree.insert(kb, vc).unwrap().is_none());
 	assert_eq!(tree.get(kb).unwrap().unwrap(), vc);
 
 	let mut iter = tree.iter().unwrap();