From b70f1ce3af2cb23fdae7b5c275d958833fe2642c Mon Sep 17 00:00:00 2001
From: Aiden McClelland <me@drbonez.dev>
Date: Tue, 27 Apr 2021 14:59:53 -0600
Subject: [PATCH] minor refactor of transactions

---
 patch-db-macro-internals/src/lib.rs |  15 ++
 patch-db/src/handle.rs              | 247 +++++++++++++++++
 patch-db/src/lib.rs                 |   4 +-
 patch-db/src/model.rs               | 101 +++++--
 patch-db/src/store.rs               |  24 +-
 patch-db/src/test.rs                |   5 +-
 patch-db/src/transaction.rs         | 400 +++++-----------------------
 7 files changed, 421 insertions(+), 375 deletions(-)
 create mode 100644 patch-db/src/handle.rs

diff --git a/patch-db-macro-internals/src/lib.rs b/patch-db-macro-internals/src/lib.rs
index 7465f10..b94a807 100644
--- a/patch-db-macro-internals/src/lib.rs
+++ b/patch-db-macro-internals/src/lib.rs
@@ -162,6 +162,11 @@ fn build_model_struct(
                             #model_name(#inner_model::from(ptr))
                         }
                     }
+                    impl From<#model_name> for patch_db::json_ptr::JsonPointer {
+                        fn from(model: #model_name) -> Self {
+                            model.0.into()
+                        }
+                    }
                     impl AsRef<patch_db::json_ptr::JsonPointer> for #model_name {
                         fn as_ref(&self) -> &patch_db::json_ptr::JsonPointer {
                             self.0.as_ref()
@@ -242,6 +247,11 @@ fn build_model_struct(
                 #model_name(From::from(ptr))
             }
         }
+        impl From<#model_name> for patch_db::json_ptr::JsonPointer {
+            fn from(model: #model_name) -> Self {
+                model.0.into()
+            }
+        }
         impl AsRef<patch_db::json_ptr::JsonPointer> for #model_name {
             fn as_ref(&self) -> &patch_db::json_ptr::JsonPointer {
                 self.0.as_ref()
@@ -281,6 +291,11 @@ fn build_model_enum(base: &DeriveInput, _: &DataEnum, model_name: Option<Ident>)
                 #model_name(From::from(ptr))
             }
         }
+        impl From<#model_name> for patch_db::json_ptr::JsonPointer {
+            fn from(model: #model_name) -> Self {
+                model.0.into()
+            }
+        }
         impl AsRef<patch_db::json_ptr::JsonPointer> for #model_name {
             fn as_ref(&self) -> &patch_db::json_ptr::JsonPointer {
                 self.0.as_ref()
diff --git a/patch-db/src/handle.rs b/patch-db/src/handle.rs
new file mode 100644
index 0000000..7ba74d0
--- /dev/null
+++ b/patch-db/src/handle.rs
@@ -0,0 +1,247 @@
+use std::sync::Arc;
+
+use async_trait::async_trait;
+use json_ptr::{JsonPointer, SegList};
+use serde::{Deserialize, Serialize};
+use serde_json::Value;
+use tokio::sync::{broadcast::Receiver, RwLock, RwLockReadGuard};
+
+use crate::{
+    locker::{LockType, LockerGuard},
+    Locker, PatchDb, Revision, Store, Transaction,
+};
+use crate::{patch::DiffPatch, Error};
+
+#[async_trait]
+pub trait DbHandle: Sized + Send + Sync {
+    async fn begin<'a>(&'a mut self) -> Result<Transaction<&'a mut Self>, Error>;
+    fn rebase(&mut self) -> Result<(), Error>;
+    fn store(&self) -> Arc<RwLock<Store>>;
+    fn subscribe(&self) -> Receiver<Arc<Revision>>;
+    fn locker_and_locks(&mut self) -> (&Locker, Vec<&mut [(JsonPointer, LockerGuard)]>);
+    async fn exists<S: AsRef<str> + Send + Sync, V: SegList + Send + Sync>(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        store_read_lock: Option<RwLockReadGuard<'_, Store>>,
+    ) -> Result<bool, Error>;
+    async fn get_value<S: AsRef<str> + Send + Sync, V: SegList + Send + Sync>(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        store_read_lock: Option<RwLockReadGuard<'_, Store>>,
+    ) -> Result<Value, Error>;
+    async fn put_value<S: AsRef<str> + Send + Sync, V: SegList + Send + Sync>(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        value: &Value,
+    ) -> Result<(), Error>;
+    async fn apply(&mut self, patch: DiffPatch) -> Result<(), Error>;
+    async fn lock<S: AsRef<str> + Clone + Send + Sync, V: SegList + Clone + Send + Sync>(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        lock: LockType,
+    ) -> ();
+    async fn get<
+        T: for<'de> Deserialize<'de>,
+        S: AsRef<str> + Send + Sync,
+        V: SegList + Send + Sync,
+    >(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+    ) -> Result<T, Error>;
+    async fn put<
+        T: Serialize + Send + Sync,
+        S: AsRef<str> + Send + Sync,
+        V: SegList + Send + Sync,
+    >(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        value: &T,
+    ) -> Result<(), Error>;
+}
+#[async_trait]
+impl<Handle: DbHandle + Send + Sync> DbHandle for &mut Handle {
+    async fn begin<'a>(&'a mut self) -> Result<Transaction<&'a mut Self>, Error> {
+        let Transaction {
+            locks,
+            updates,
+            sub,
+            ..
+        } = (*self).begin().await?;
+        Ok(Transaction {
+            parent: self,
+            locks,
+            updates,
+            sub,
+        })
+    }
+    fn rebase(&mut self) -> Result<(), Error> {
+        (*self).rebase()
+    }
+    fn store(&self) -> Arc<RwLock<Store>> {
+        (**self).store()
+    }
+    fn subscribe(&self) -> Receiver<Arc<Revision>> {
+        (**self).subscribe()
+    }
+    fn locker_and_locks(&mut self) -> (&Locker, Vec<&mut [(JsonPointer, LockerGuard)]>) {
+        (*self).locker_and_locks()
+    }
+    async fn exists<S: AsRef<str> + Send + Sync, V: SegList + Send + Sync>(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        store_read_lock: Option<RwLockReadGuard<'_, Store>>,
+    ) -> Result<bool, Error> {
+        (*self).exists(ptr, store_read_lock).await
+    }
+    async fn get_value<S: AsRef<str> + Send + Sync, V: SegList + Send + Sync>(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        store_read_lock: Option<RwLockReadGuard<'_, Store>>,
+    ) -> Result<Value, Error> {
+        (*self).get_value(ptr, store_read_lock).await
+    }
+    async fn put_value<S: AsRef<str> + Send + Sync, V: SegList + Send + Sync>(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        value: &Value,
+    ) -> Result<(), Error> {
+        (*self).put_value(ptr, value).await
+    }
+    async fn apply(&mut self, patch: DiffPatch) -> Result<(), Error> {
+        (*self).apply(patch).await
+    }
+    async fn lock<S: AsRef<str> + Clone + Send + Sync, V: SegList + Clone + Send + Sync>(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        lock: LockType,
+    ) {
+        (*self).lock(ptr, lock).await
+    }
+    async fn get<
+        T: for<'de> Deserialize<'de>,
+        S: AsRef<str> + Send + Sync,
+        V: SegList + Send + Sync,
+    >(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+    ) -> Result<T, Error> {
+        (*self).get(ptr).await
+    }
+    async fn put<
+        T: Serialize + Send + Sync,
+        S: AsRef<str> + Send + Sync,
+        V: SegList + Send + Sync,
+    >(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        value: &T,
+    ) -> Result<(), Error> {
+        (*self).put(ptr, value).await
+    }
+}
+
+pub struct PatchDbHandle {
+    pub(crate) db: PatchDb,
+    pub(crate) locks: Vec<(JsonPointer, LockerGuard)>,
+}
+
+#[async_trait]
+impl DbHandle for PatchDbHandle {
+    async fn begin<'a>(&'a mut self) -> Result<Transaction<&'a mut Self>, Error> {
+        Ok(Transaction {
+            sub: self.subscribe(),
+            parent: self,
+            locks: Vec::new(),
+            updates: DiffPatch::default(),
+        })
+    }
+    fn rebase(&mut self) -> Result<(), Error> {
+        Ok(())
+    }
+    fn store(&self) -> Arc<RwLock<Store>> {
+        self.db.store.clone()
+    }
+    fn subscribe(&self) -> Receiver<Arc<Revision>> {
+        self.db.subscribe()
+    }
+    fn locker_and_locks(&mut self) -> (&Locker, Vec<&mut [(JsonPointer, LockerGuard)]>) {
+        (&self.db.locker, vec![self.locks.as_mut_slice()])
+    }
+    async fn exists<S: AsRef<str> + Send + Sync, V: SegList + Send + Sync>(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        store_read_lock: Option<RwLockReadGuard<'_, Store>>,
+    ) -> Result<bool, Error> {
+        if let Some(lock) = store_read_lock {
+            lock.exists(ptr)
+        } else {
+            self.db.exists(ptr).await
+        }
+    }
+    async fn get_value<S: AsRef<str> + Send + Sync, V: SegList + Send + Sync>(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        store_read_lock: Option<RwLockReadGuard<'_, Store>>,
+    ) -> Result<Value, Error> {
+        if let Some(lock) = store_read_lock {
+            lock.get(ptr)
+        } else {
+            self.db.get(ptr).await
+        }
+    }
+    async fn put_value<S: AsRef<str> + Send + Sync, V: SegList + Send + Sync>(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        value: &Value,
+    ) -> Result<(), Error> {
+        self.db.put(ptr, value).await?;
+        Ok(())
+    }
+    async fn apply(&mut self, patch: DiffPatch) -> Result<(), Error> {
+        self.db.apply(patch, None).await?;
+        Ok(())
+    }
+    async fn lock<S: AsRef<str> + Clone + Send + Sync, V: SegList + Clone + Send + Sync>(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        lock: LockType,
+    ) {
+        match lock {
+            LockType::Read => {
+                self.db
+                    .locker
+                    .add_read_lock(ptr, &mut self.locks, &mut [])
+                    .await;
+            }
+            LockType::Write => {
+                self.db
+                    .locker
+                    .add_write_lock(ptr, &mut self.locks, &mut [])
+                    .await;
+            }
+            LockType::None => (),
+        }
+    }
+    async fn get<
+        T: for<'de> Deserialize<'de>,
+        S: AsRef<str> + Send + Sync,
+        V: SegList + Send + Sync,
+    >(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+    ) -> Result<T, Error> {
+        self.db.get(ptr).await
+    }
+    async fn put<
+        T: Serialize + Send + Sync,
+        S: AsRef<str> + Send + Sync,
+        V: SegList + Send + Sync,
+    >(
+        &mut self,
+        ptr: &JsonPointer<S, V>,
+        value: &T,
+    ) -> Result<(), Error> {
+        self.db.put(ptr, value).await?;
+        Ok(())
+    }
+}
diff --git a/patch-db/src/lib.rs b/patch-db/src/lib.rs
index 872fbc8..0d1501f 100644
--- a/patch-db/src/lib.rs
+++ b/patch-db/src/lib.rs
@@ -6,6 +6,7 @@ use tokio::sync::broadcast::error::TryRecvError;
 
 // note: inserting into an array (before another element) without proper locking can result in unexpected behaviour
 
+mod handle;
 mod locker;
 mod model;
 mod patch;
@@ -15,6 +16,7 @@ mod transaction;
 #[cfg(test)]
 mod test;
 
+pub use handle::{DbHandle, PatchDbHandle};
 pub use json_ptr;
 pub use locker::{LockType, Locker};
 pub use model::{
@@ -23,7 +25,7 @@ pub use model::{
 pub use patch::Revision;
 pub use patch_db_macro::HasModel;
 pub use store::{PatchDb, Store};
-pub use transaction::{Checkpoint, SubTransaction, Transaction};
+pub use transaction::Transaction;
 
 #[derive(Error, Debug)]
 pub enum Error {
diff --git a/patch-db/src/model.rs b/patch-db/src/model.rs
index bb304ce..310e415 100644
--- a/patch-db/src/model.rs
+++ b/patch-db/src/model.rs
@@ -7,9 +7,8 @@ use json_ptr::JsonPointer;
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
 
-use crate::locker::LockType;
-use crate::transaction::Checkpoint;
 use crate::Error;
+use crate::{locker::LockType, DbHandle};
 
 pub struct ModelData<T: Serialize + for<'de> Deserialize<'de>>(T);
 impl<T: Serialize + for<'de> Deserialize<'de>> Deref for ModelData<T> {
@@ -25,13 +24,13 @@ pub struct ModelDataMut<T: Serialize + for<'de> Deserialize<'de>> {
     ptr: JsonPointer,
 }
 impl<T: Serialize + for<'de> Deserialize<'de>> ModelDataMut<T> {
-    pub async fn save<Tx: Checkpoint>(self, tx: &mut Tx) -> Result<(), Error> {
+    pub async fn save<Db: DbHandle>(self, db: &mut Db) -> Result<(), Error> {
         let current = serde_json::to_value(&self.current)?;
         let mut diff = crate::patch::diff(&self.original, &current);
-        let target = tx.get_value(&self.ptr, None).await?;
+        let target = db.get_value(&self.ptr, None).await?;
         diff.rebase(&crate::patch::diff(&self.original, &target));
         diff.prepend(&self.ptr);
-        tx.apply(diff);
+        db.apply(diff).await?;
         Ok(())
     }
 }
@@ -56,17 +55,18 @@ impl<T> Model<T>
 where
     T: Serialize + for<'de> Deserialize<'de>,
 {
-    pub async fn lock<Tx: Checkpoint>(&self, tx: &mut Tx, lock: LockType) {
-        tx.lock(&self.ptr, lock).await
+    pub async fn lock<Db: DbHandle>(&self, db: &mut Db, lock: LockType) {
+        db.lock(&self.ptr, lock).await
     }
 
-    pub async fn get<Tx: Checkpoint>(&self, tx: &mut Tx) -> Result<ModelData<T>, Error> {
-        Ok(ModelData(tx.get(&self.ptr, LockType::Read).await?))
+    pub async fn get<Db: DbHandle>(&self, db: &mut Db) -> Result<ModelData<T>, Error> {
+        db.lock(&self.ptr, LockType::Read).await;
+        Ok(ModelData(db.get(&self.ptr).await?))
     }
 
-    pub async fn get_mut<Tx: Checkpoint>(&self, tx: &mut Tx) -> Result<ModelDataMut<T>, Error> {
-        self.lock(tx, LockType::Write).await;
-        let original = tx.get_value(&self.ptr, None).await?;
+    pub async fn get_mut<Db: DbHandle>(&self, db: &mut Db) -> Result<ModelDataMut<T>, Error> {
+        self.lock(db, LockType::Write).await;
+        let original = db.get_value(&self.ptr, None).await?;
         let current = serde_json::from_value(original.clone())?;
         Ok(ModelDataMut {
             original,
@@ -88,9 +88,9 @@ impl<T> Model<T>
 where
     T: Serialize + for<'de> Deserialize<'de> + Send + Sync,
 {
-    pub async fn put<Tx: Checkpoint>(&self, tx: &mut Tx, value: &T) -> Result<(), Error> {
-        self.lock(tx, LockType::Write).await;
-        tx.put(&self.ptr, value).await
+    pub async fn put<Db: DbHandle>(&self, db: &mut Db, value: &T) -> Result<(), Error> {
+        self.lock(db, LockType::Write).await;
+        db.put(&self.ptr, value).await
     }
 }
 impl<T> From<JsonPointer> for Model<T>
@@ -132,8 +132,8 @@ where
     }
 }
 
-pub trait HasModel {
-    type Model: From<JsonPointer> + AsRef<JsonPointer>;
+pub trait HasModel: Serialize + for<'de> Deserialize<'de> {
+    type Model: From<JsonPointer> + AsRef<JsonPointer> + Into<JsonPointer> + From<Model<Self>>;
 }
 
 #[derive(Debug, Clone)]
@@ -162,6 +162,11 @@ impl<T: HasModel + Serialize + for<'de> Deserialize<'de>> From<JsonPointer> for
         BoxModel(T::Model::from(ptr))
     }
 }
+impl<T: HasModel + Serialize + for<'de> Deserialize<'de>> From<BoxModel<T>> for JsonPointer {
+    fn from(model: BoxModel<T>) -> Self {
+        model.0.into()
+    }
+}
 impl<T: HasModel + Serialize + for<'de> Deserialize<'de>> HasModel for Box<T> {
     type Model = BoxModel<T>;
 }
@@ -169,13 +174,32 @@ impl<T: HasModel + Serialize + for<'de> Deserialize<'de>> HasModel for Box<T> {
 #[derive(Debug, Clone)]
 pub struct OptionModel<T: HasModel + Serialize + for<'de> Deserialize<'de>>(T::Model);
 impl<T: HasModel + Serialize + for<'de> Deserialize<'de>> OptionModel<T> {
-    pub async fn check<Tx: Checkpoint>(self, tx: &mut Tx) -> Result<Option<T::Model>, Error> {
-        Ok(if tx.exists(self.0.as_ref(), None).await? {
+    pub async fn exists<Db: DbHandle>(&self, db: &mut Db) -> Result<bool, Error> {
+        db.lock(self.as_ref(), LockType::Read).await;
+        Ok(db.exists(&self.as_ref(), None).await?)
+    }
+
+    pub async fn check<Db: DbHandle>(self, db: &mut Db) -> Result<Option<T::Model>, Error> {
+        Ok(if self.exists(db).await? {
             Some(self.0)
         } else {
             None
         })
     }
+
+    pub async fn delete<Db: DbHandle>(&self, db: &mut Db) -> Result<(), Error> {
+        db.lock(self.as_ref(), LockType::Write).await;
+        db.put(self.as_ref(), &Value::Null).await
+    }
+}
+impl<T> OptionModel<T>
+where
+    T: Serialize + for<'de> Deserialize<'de> + Send + Sync + HasModel,
+{
+    pub async fn put<Db: DbHandle>(&self, db: &mut Db, value: &T) -> Result<(), Error> {
+        db.lock(self.as_ref(), LockType::Write).await;
+        db.put(self.as_ref(), value).await
+    }
 }
 impl<T: HasModel + Serialize + for<'de> Deserialize<'de>> From<Model<Option<T>>>
     for OptionModel<T>
@@ -189,8 +213,18 @@ impl<T: HasModel + Serialize + for<'de> Deserialize<'de>> From<JsonPointer> for
         OptionModel(T::Model::from(ptr))
     }
 }
+impl<T: HasModel + Serialize + for<'de> Deserialize<'de>> From<OptionModel<T>> for JsonPointer {
+    fn from(model: OptionModel<T>) -> Self {
+        model.0.into()
+    }
+}
+impl<T: HasModel + Serialize + for<'de> Deserialize<'de>> AsRef<JsonPointer> for OptionModel<T> {
+    fn as_ref(&self) -> &JsonPointer {
+        self.0.as_ref()
+    }
+}
 impl<T: HasModel + Serialize + for<'de> Deserialize<'de>> HasModel for Option<T> {
-    type Model = BoxModel<T>;
+    type Model = OptionModel<T>;
 }
 
 #[derive(Debug, Clone)]
@@ -216,6 +250,11 @@ impl<T: Serialize + for<'de> Deserialize<'de>> From<JsonPointer> for VecModel<T>
         VecModel(From::from(ptr))
     }
 }
+impl<T: Serialize + for<'de> Deserialize<'de>> From<VecModel<T>> for JsonPointer {
+    fn from(model: VecModel<T>) -> Self {
+        model.0.into()
+    }
+}
 impl<T> AsRef<JsonPointer> for VecModel<T>
 where
     T: Serialize + for<'de> Deserialize<'de>,
@@ -282,6 +321,15 @@ where
         self.child(idx.as_ref()).into()
     }
 }
+impl<T> From<Model<T>> for MapModel<T>
+where
+    T: Serialize + for<'de> Deserialize<'de> + Map,
+    T::Value: Serialize + for<'de> Deserialize<'de>,
+{
+    fn from(model: Model<T>) -> Self {
+        MapModel(model)
+    }
+}
 impl<T> From<JsonPointer> for MapModel<T>
 where
     T: Serialize + for<'de> Deserialize<'de> + Map,
@@ -291,6 +339,15 @@ where
         MapModel(From::from(ptr))
     }
 }
+impl<T> From<MapModel<T>> for JsonPointer
+where
+    T: Serialize + for<'de> Deserialize<'de> + Map,
+    T::Value: Serialize + for<'de> Deserialize<'de>,
+{
+    fn from(model: MapModel<T>) -> Self {
+        model.0.into()
+    }
+}
 impl<T> AsRef<JsonPointer> for MapModel<T>
 where
     T: Serialize + for<'de> Deserialize<'de> + Map,
@@ -309,8 +366,8 @@ where
 }
 impl<K, V> HasModel for BTreeMap<K, V>
 where
-    K: Serialize + for<'de> Deserialize<'de> + Hash + Eq + AsRef<str>,
+    K: Serialize + for<'de> Deserialize<'de> + Ord + AsRef<str>,
     V: Serialize + for<'de> Deserialize<'de>,
 {
-    type Model = MapModel<HashMap<K, V>>;
+    type Model = MapModel<BTreeMap<K, V>>;
 }
diff --git a/patch-db/src/store.rs b/patch-db/src/store.rs
index 9c0ae34..37e05c2 100644
--- a/patch-db/src/store.rs
+++ b/patch-db/src/store.rs
@@ -14,10 +14,9 @@ use tokio::fs::File;
 use tokio::sync::broadcast::{Receiver, Sender};
 use tokio::sync::{Mutex, RwLock, RwLockWriteGuard};
 
-use crate::locker::Locker;
 use crate::patch::{diff, DiffPatch, Revision};
-use crate::transaction::Transaction;
 use crate::Error;
+use crate::{locker::Locker, PatchDbHandle};
 
 lazy_static! {
     static ref OPEN_STORES: Mutex<HashMap<PathBuf, Qutex<()>>> = Mutex::new(HashMap::new());
@@ -31,7 +30,7 @@ pub struct Store {
     revision: u64,
 }
 impl Store {
-    pub async fn open<P: AsRef<Path>>(path: P) -> Result<Self, Error> {
+    pub(crate) async fn open<P: AsRef<Path>>(path: P) -> Result<Self, Error> {
         let (_lock, path) = {
             if !path.as_ref().exists() {
                 tokio::fs::File::create(path.as_ref()).await?;
@@ -123,13 +122,13 @@ impl Store {
         self.file.unlock(true).map_err(|e| e.1)?;
         Ok(())
     }
-    pub fn exists<S: AsRef<str>, V: SegList>(
+    pub(crate) fn exists<S: AsRef<str>, V: SegList>(
         &self,
         ptr: &JsonPointer<S, V>,
     ) -> Result<bool, Error> {
         Ok(ptr.get(self.get_data()?).unwrap_or(&Value::Null) != &Value::Null)
     }
-    pub fn get<T: for<'de> Deserialize<'de>, S: AsRef<str>, V: SegList>(
+    pub(crate) fn get<T: for<'de> Deserialize<'de>, S: AsRef<str>, V: SegList>(
         &self,
         ptr: &JsonPointer<S, V>,
     ) -> Result<T, Error> {
@@ -137,10 +136,10 @@ impl Store {
             ptr.get(self.get_data()?).unwrap_or(&Value::Null).clone(),
         )?)
     }
-    pub fn dump(&self) -> Value {
+    pub(crate) fn dump(&self) -> Value {
         self.get_data().unwrap().clone()
     }
-    pub async fn put<T: Serialize + ?Sized, S: AsRef<str>, V: SegList>(
+    pub(crate) async fn put<T: Serialize + ?Sized, S: AsRef<str>, V: SegList>(
         &mut self,
         ptr: &JsonPointer<S, V>,
         value: &T,
@@ -152,7 +151,7 @@ impl Store {
         patch.prepend(ptr);
         self.apply(patch).await
     }
-    pub async fn apply(&mut self, patch: DiffPatch) -> Result<Arc<Revision>, Error> {
+    pub(crate) async fn apply(&mut self, patch: DiffPatch) -> Result<Arc<Revision>, Error> {
         use tokio::io::AsyncWriteExt;
 
         self.check_cache_corrupted()?;
@@ -196,6 +195,9 @@ impl PatchDb {
             subscriber: Arc::new(subscriber),
         })
     }
+    pub async fn dump(&self) -> Value {
+        self.store.read().await.dump()
+    }
     pub async fn exists<S: AsRef<str>, V: SegList>(
         &self,
         ptr: &JsonPointer<S, V>,
@@ -235,12 +237,10 @@ impl PatchDb {
     pub fn subscribe(&self) -> Receiver<Arc<Revision>> {
         self.subscriber.subscribe()
     }
-    pub fn begin(&self) -> Transaction {
-        Transaction {
+    pub fn handle(&self) -> PatchDbHandle {
+        PatchDbHandle {
             db: self.clone(),
             locks: Vec::new(),
-            updates: DiffPatch::default(),
-            sub: self.subscribe(),
         }
     }
 }
diff --git a/patch-db/src/test.rs b/patch-db/src/test.rs
index a467ca4..19abb41 100644
--- a/patch-db/src/test.rs
+++ b/patch-db/src/test.rs
@@ -8,7 +8,7 @@ use serde_json::Value;
 use tokio::fs;
 use tokio::runtime::Builder;
 
-use crate as patch_db;
+use crate::{self as patch_db, DbHandle};
 
 async fn init_db(db_name: String) -> PatchDb {
     cleanup_db(&db_name).await;
@@ -54,7 +54,8 @@ async fn basic() {
 #[tokio::test]
 async fn transaction() {
     let db = init_db("test.db".to_string()).await;
-    let mut tx = db.begin();
+    let mut handle = db.handle();
+    let mut tx = handle.begin().await.unwrap();
     let ptr: JsonPointer = "/b/b".parse().unwrap();
     tx.put(&ptr, &(2 as usize)).await.unwrap();
     tx.put(&ptr, &(1 as usize)).await.unwrap();
diff --git a/patch-db/src/transaction.rs b/patch-db/src/transaction.rs
index 3c20aeb..3e13f5c 100644
--- a/patch-db/src/transaction.rs
+++ b/patch-db/src/transaction.rs
@@ -1,6 +1,6 @@
 use std::sync::Arc;
 
-use futures::future::{BoxFuture, FutureExt};
+use async_trait::async_trait;
 use json_ptr::{JsonPointer, SegList};
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
@@ -8,258 +8,59 @@ use tokio::sync::broadcast::error::TryRecvError;
 use tokio::sync::broadcast::Receiver;
 use tokio::sync::{RwLock, RwLockReadGuard};
 
-use crate::locker::{LockType, Locker, LockerGuard};
-use crate::patch::{DiffPatch, Revision};
-use crate::store::{PatchDb, Store};
+use crate::store::Store;
 use crate::Error;
+use crate::{
+    locker::{LockType, Locker, LockerGuard},
+    DbHandle,
+};
+use crate::{
+    patch::{DiffPatch, Revision},
+    PatchDbHandle,
+};
 
-pub trait Checkpoint: Sized {
-    fn rebase(&mut self) -> Result<(), Error>;
-    fn exists<'a, S: AsRef<str> + Send + Sync + 'a, V: SegList + Send + Sync + 'a>(
-        &'a mut self,
-        ptr: &'a JsonPointer<S, V>,
-        store_read_lock: Option<RwLockReadGuard<'a, Store>>,
-    ) -> BoxFuture<'a, Result<bool, Error>>;
-    fn get_value<'a, S: AsRef<str> + Send + Sync + 'a, V: SegList + Send + Sync + 'a>(
-        &'a mut self,
-        ptr: &'a JsonPointer<S, V>,
-        store_read_lock: Option<RwLockReadGuard<'a, Store>>,
-    ) -> BoxFuture<'a, Result<Value, Error>>;
-    fn put_value<'a, S: AsRef<str> + Send + Sync + 'a, V: SegList + Send + Sync + 'a>(
-        &'a mut self,
-        ptr: &'a JsonPointer<S, V>,
-        value: &'a Value,
-    ) -> BoxFuture<'a, Result<(), Error>>;
-    fn store(&self) -> Arc<RwLock<Store>>;
-    fn subscribe(&self) -> Receiver<Arc<Revision>>;
-    fn locker_and_locks(&mut self) -> (&Locker, Vec<&mut [(JsonPointer, LockerGuard)]>);
-    fn apply(&mut self, patch: DiffPatch);
-    fn lock<'a, S: AsRef<str> + Clone + Send + Sync, V: SegList + Clone + Send + Sync>(
-        &'a mut self,
-        ptr: &'a JsonPointer<S, V>,
-        lock: LockType,
-    ) -> BoxFuture<'a, ()>;
-    fn get<
-        'a,
-        T: for<'de> Deserialize<'de> + 'a,
-        S: AsRef<str> + Clone + Send + Sync + 'a,
-        V: SegList + Clone + Send + Sync + 'a,
-    >(
-        &'a mut self,
-        ptr: &'a JsonPointer<S, V>,
-        lock: LockType,
-    ) -> BoxFuture<'a, Result<T, Error>>;
-    fn put<
-        'a,
-        T: Serialize + Send + Sync + 'a,
-        S: AsRef<str> + Send + Sync + 'a,
-        V: SegList + Send + Sync + 'a,
-    >(
-        &'a mut self,
-        ptr: &'a JsonPointer<S, V>,
-        value: &'a T,
-    ) -> BoxFuture<'a, Result<(), Error>>;
-}
-
-pub struct Transaction {
-    pub(crate) db: PatchDb,
+pub struct Transaction<Parent: DbHandle> {
+    pub(crate) parent: Parent,
     pub(crate) locks: Vec<(JsonPointer, LockerGuard)>,
     pub(crate) updates: DiffPatch,
     pub(crate) sub: Receiver<Arc<Revision>>,
 }
-impl Transaction {
-    pub fn rebase(&mut self) -> Result<(), Error> {
-        while let Some(rev) = match self.sub.try_recv() {
-            Ok(a) => Some(a),
-            Err(TryRecvError::Empty) => None,
-            Err(e) => return Err(e.into()),
-        } {
-            self.updates.rebase(&rev.patch);
-        }
-        Ok(())
-    }
-    async fn exists<S: AsRef<str>, V: SegList>(
-        &mut self,
-        ptr: &JsonPointer<S, V>,
-        store_read_lock: Option<RwLockReadGuard<'_, Store>>,
-    ) -> Result<bool, Error> {
-        let exists = {
-            let store_lock = self.db.store.clone();
-            let store = if let Some(store_read_lock) = store_read_lock {
-                store_read_lock
-            } else {
-                store_lock.read().await
-            };
-            self.rebase()?;
-            ptr.get(store.get_data()?).unwrap_or(&Value::Null) != &Value::Null
-        };
-        Ok(self.updates.for_path(ptr).exists().unwrap_or(exists))
-    }
-    async fn get_value<S: AsRef<str>, V: SegList>(
-        &mut self,
-        ptr: &JsonPointer<S, V>,
-        store_read_lock: Option<RwLockReadGuard<'_, Store>>,
-    ) -> Result<Value, Error> {
-        let mut data = {
-            let store_lock = self.db.store.clone();
-            let store = if let Some(store_read_lock) = store_read_lock {
-                store_read_lock
-            } else {
-                store_lock.read().await
-            };
-            self.rebase()?;
-            ptr.get(store.get_data()?).cloned().unwrap_or_default()
-        };
-        json_patch::patch(&mut data, &*self.updates.for_path(ptr))?;
-        Ok(data)
-    }
-    async fn put_value<S: AsRef<str>, V: SegList>(
-        &mut self,
-        ptr: &JsonPointer<S, V>,
-        value: &Value,
-    ) -> Result<(), Error> {
-        let old = Transaction::get_value(self, ptr, None).await?;
-        let mut patch = crate::patch::diff(&old, &value);
-        patch.prepend(ptr);
-        self.updates.append(patch);
-        Ok(())
-    }
-    pub async fn lock<S: AsRef<str> + Clone, V: SegList + Clone>(
-        &mut self,
-        ptr: &JsonPointer<S, V>,
-        lock: LockType,
-    ) {
-        match lock {
-            LockType::None => (),
-            LockType::Read => {
-                self.db
-                    .locker
-                    .add_read_lock(ptr, &mut self.locks, &mut [])
-                    .await
-            }
-            LockType::Write => {
-                self.db
-                    .locker
-                    .add_write_lock(ptr, &mut self.locks, &mut [])
-                    .await
-            }
-        }
-    }
-    pub async fn get<T: for<'de> Deserialize<'de>, S: AsRef<str> + Clone, V: SegList + Clone>(
-        &mut self,
-        ptr: &JsonPointer<S, V>,
-        lock: LockType,
-    ) -> Result<T, Error> {
-        self.lock(ptr, lock).await;
-        Ok(serde_json::from_value(
-            Transaction::get_value(self, ptr, None).await?,
-        )?)
-    }
-    pub async fn put<T: Serialize, S: AsRef<str>, V: SegList>(
-        &mut self,
-        ptr: &JsonPointer<S, V>,
-        value: &T,
-    ) -> Result<(), Error> {
-        Transaction::put_value(self, ptr, &serde_json::to_value(value)?).await
-    }
+impl Transaction<&mut PatchDbHandle> {
     pub async fn commit(mut self) -> Result<Arc<Revision>, Error> {
-        let store_lock = self.db.store.clone();
-        let store = store_lock.write().await;
-        self.rebase()?;
-        self.db.apply(self.updates, Some(store)).await
-    }
-    pub async fn begin(&mut self) -> Result<SubTransaction<&mut Self>, Error> {
-        let store_lock = self.db.store.clone();
+        let store_lock = self.parent.store();
         let store = store_lock.read().await;
         self.rebase()?;
-        let sub = self.db.subscribe();
+        let rev = self.parent.db.apply(self.updates, None).await?;
         drop(store);
-        Ok(SubTransaction {
+        Ok(rev)
+    }
+}
+impl<Parent: DbHandle + Send + Sync> Transaction<Parent> {
+    pub async fn save(mut self) -> Result<(), Error> {
+        let store_lock = self.parent.store();
+        let store = store_lock.read().await;
+        self.rebase()?;
+        self.parent.apply(self.updates).await?;
+        drop(store);
+        Ok(())
+    }
+}
+#[async_trait]
+impl<Parent: DbHandle + Send + Sync> DbHandle for Transaction<Parent> {
+    async fn begin<'a>(&'a mut self) -> Result<Transaction<&'a mut Self>, Error> {
+        let store_lock = self.parent.store();
+        let store = store_lock.read().await;
+        self.rebase()?;
+        let sub = self.parent.subscribe();
+        drop(store);
+        Ok(Transaction {
             parent: self,
             locks: Vec::new(),
             updates: DiffPatch::default(),
             sub,
         })
     }
-}
-impl<'a> Checkpoint for &'a mut Transaction {
     fn rebase(&mut self) -> Result<(), Error> {
-        Transaction::rebase(self)
-    }
-    fn exists<'b, S: AsRef<str> + Send + Sync + 'b, V: SegList + Send + Sync + 'b>(
-        &'b mut self,
-        ptr: &'b JsonPointer<S, V>,
-        store_read_lock: Option<RwLockReadGuard<'b, Store>>,
-    ) -> BoxFuture<'b, Result<bool, Error>> {
-        Transaction::exists(self, ptr, store_read_lock).boxed()
-    }
-    fn get_value<'b, S: AsRef<str> + Send + Sync + 'b, V: SegList + Send + Sync + 'b>(
-        &'b mut self,
-        ptr: &'b JsonPointer<S, V>,
-        store_read_lock: Option<RwLockReadGuard<'b, Store>>,
-    ) -> BoxFuture<'b, Result<Value, Error>> {
-        Transaction::get_value(self, ptr, store_read_lock).boxed()
-    }
-    fn put_value<'b, S: AsRef<str> + Send + Sync + 'b, V: SegList + Send + Sync + 'b>(
-        &'b mut self,
-        ptr: &'b JsonPointer<S, V>,
-        value: &'b Value,
-    ) -> BoxFuture<'b, Result<(), Error>> {
-        Transaction::put_value(self, ptr, value).boxed()
-    }
-    fn store(&self) -> Arc<RwLock<Store>> {
-        self.db.store.clone()
-    }
-    fn subscribe(&self) -> Receiver<Arc<Revision>> {
-        self.db.subscribe()
-    }
-    fn locker_and_locks(&mut self) -> (&Locker, Vec<&mut [(JsonPointer, LockerGuard)]>) {
-        (&self.db.locker, vec![&mut self.locks])
-    }
-    fn apply(&mut self, patch: DiffPatch) {
-        self.updates.append(patch)
-    }
-    fn lock<'b, S: AsRef<str> + Clone + Send + Sync, V: SegList + Clone + Send + Sync>(
-        &'b mut self,
-        ptr: &'b JsonPointer<S, V>,
-        lock: LockType,
-    ) -> BoxFuture<'b, ()> {
-        Transaction::lock(self, ptr, lock).boxed()
-    }
-    fn get<
-        'b,
-        T: for<'de> Deserialize<'de> + 'b,
-        S: AsRef<str> + Clone + Send + Sync + 'b,
-        V: SegList + Clone + Send + Sync + 'b,
-    >(
-        &'b mut self,
-        ptr: &'b JsonPointer<S, V>,
-        lock: LockType,
-    ) -> BoxFuture<'b, Result<T, Error>> {
-        Transaction::get(self, ptr, lock).boxed()
-    }
-    fn put<
-        'b,
-        T: Serialize + Send + Sync + 'b,
-        S: AsRef<str> + Send + Sync + 'b,
-        V: SegList + Send + Sync + 'b,
-    >(
-        &'b mut self,
-        ptr: &'b JsonPointer<S, V>,
-        value: &'b T,
-    ) -> BoxFuture<'b, Result<(), Error>> {
-        Transaction::put(self, ptr, value).boxed()
-    }
-}
-
-pub struct SubTransaction<Tx: Checkpoint> {
-    parent: Tx,
-    locks: Vec<(JsonPointer, LockerGuard)>,
-    updates: DiffPatch,
-    sub: Receiver<Arc<Revision>>,
-}
-impl<Tx: Checkpoint + Send + Sync> SubTransaction<Tx> {
-    pub fn rebase(&mut self) -> Result<(), Error> {
         self.parent.rebase()?;
         while let Some(rev) = match self.sub.try_recv() {
             Ok(a) => Some(a),
@@ -270,6 +71,17 @@ impl<Tx: Checkpoint + Send + Sync> SubTransaction<Tx> {
         }
         Ok(())
     }
+    fn store(&self) -> Arc<RwLock<Store>> {
+        self.parent.store()
+    }
+    fn subscribe(&self) -> Receiver<Arc<Revision>> {
+        self.parent.subscribe()
+    }
+    fn locker_and_locks(&mut self) -> (&Locker, Vec<&mut [(JsonPointer, LockerGuard)]>) {
+        let (locker, mut locks) = self.parent.locker_and_locks();
+        locks.push(&mut self.locks);
+        (locker, locks)
+    }
     async fn exists<S: AsRef<str> + Send + Sync, V: SegList + Send + Sync>(
         &mut self,
         ptr: &JsonPointer<S, V>,
@@ -310,13 +122,13 @@ impl<Tx: Checkpoint + Send + Sync> SubTransaction<Tx> {
         ptr: &JsonPointer<S, V>,
         value: &Value,
     ) -> Result<(), Error> {
-        let old = SubTransaction::get_value(self, ptr, None).await?;
+        let old = self.get_value(ptr, None).await?;
         let mut patch = crate::patch::diff(&old, &value);
         patch.prepend(ptr);
         self.updates.append(patch);
         Ok(())
     }
-    pub async fn lock<S: AsRef<str> + Clone, V: SegList + Clone>(
+    async fn lock<S: AsRef<str> + Clone + Send + Sync, V: SegList + Clone + Send + Sync>(
         &mut self,
         ptr: &JsonPointer<S, V>,
         lock: LockType,
@@ -335,117 +147,29 @@ impl<Tx: Checkpoint + Send + Sync> SubTransaction<Tx> {
             }
         }
     }
-    pub async fn get<
+    async fn get<
         T: for<'de> Deserialize<'de>,
-        S: AsRef<str> + Clone + Send + Sync,
-        V: SegList + Clone + Send + Sync,
+        S: AsRef<str> + Send + Sync,
+        V: SegList + Send + Sync,
     >(
         &mut self,
         ptr: &JsonPointer<S, V>,
-        lock: LockType,
     ) -> Result<T, Error> {
-        self.lock(ptr, lock).await;
-        Ok(serde_json::from_value(
-            SubTransaction::get_value(self, ptr, None).await?,
-        )?)
+        Ok(serde_json::from_value(self.get_value(ptr, None).await?)?)
     }
-    pub async fn put<T: Serialize, S: AsRef<str> + Send + Sync, V: SegList + Send + Sync>(
+    async fn put<
+        T: Serialize + Send + Sync,
+        S: AsRef<str> + Send + Sync,
+        V: SegList + Send + Sync,
+    >(
         &mut self,
         ptr: &JsonPointer<S, V>,
         value: &T,
     ) -> Result<(), Error> {
-        SubTransaction::put_value(self, ptr, &serde_json::to_value(value)?).await
+        self.put_value(ptr, &serde_json::to_value(value)?).await
     }
-    pub async fn commit(mut self) -> Result<(), Error> {
-        let store_lock = self.parent.store();
-        let store = store_lock.read().await;
-        self.rebase()?;
-        self.parent.apply(self.updates);
-        drop(store);
+    async fn apply(&mut self, patch: DiffPatch) -> Result<(), Error> {
+        self.updates.append(patch);
         Ok(())
     }
-    pub async fn begin(&mut self) -> Result<SubTransaction<&mut Self>, Error> {
-        let store_lock = self.parent.store();
-        let store = store_lock.read().await;
-        self.rebase()?;
-        let sub = self.parent.subscribe();
-        drop(store);
-        Ok(SubTransaction {
-            parent: self,
-            locks: Vec::new(),
-            updates: DiffPatch::default(),
-            sub,
-        })
-    }
-}
-impl<'a, Tx: Checkpoint + Send + Sync> Checkpoint for &'a mut SubTransaction<Tx> {
-    fn rebase(&mut self) -> Result<(), Error> {
-        SubTransaction::rebase(self)
-    }
-    fn exists<'b, S: AsRef<str> + Send + Sync + 'b, V: SegList + Send + Sync + 'b>(
-        &'b mut self,
-        ptr: &'b JsonPointer<S, V>,
-        store_read_lock: Option<RwLockReadGuard<'b, Store>>,
-    ) -> BoxFuture<'b, Result<bool, Error>> {
-        SubTransaction::exists(self, ptr, store_read_lock).boxed()
-    }
-    fn get_value<'b, S: AsRef<str> + Send + Sync + 'b, V: SegList + Send + Sync + 'b>(
-        &'b mut self,
-        ptr: &'b JsonPointer<S, V>,
-        store_read_lock: Option<RwLockReadGuard<'b, Store>>,
-    ) -> BoxFuture<'b, Result<Value, Error>> {
-        SubTransaction::get_value(self, ptr, store_read_lock).boxed()
-    }
-    fn put_value<'b, S: AsRef<str> + Send + Sync + 'b, V: SegList + Send + Sync + 'b>(
-        &'b mut self,
-        ptr: &'b JsonPointer<S, V>,
-        value: &'b Value,
-    ) -> BoxFuture<'b, Result<(), Error>> {
-        SubTransaction::put_value(self, ptr, value).boxed()
-    }
-    fn store(&self) -> Arc<RwLock<Store>> {
-        self.parent.store()
-    }
-    fn subscribe(&self) -> Receiver<Arc<Revision>> {
-        self.parent.subscribe()
-    }
-    fn locker_and_locks(&mut self) -> (&Locker, Vec<&mut [(JsonPointer, LockerGuard)]>) {
-        let (locker, mut locks) = self.parent.locker_and_locks();
-        locks.push(&mut self.locks);
-        (locker, locks)
-    }
-    fn apply(&mut self, patch: DiffPatch) {
-        self.updates.append(patch)
-    }
-    fn lock<'b, S: AsRef<str> + Clone + Send + Sync, V: SegList + Clone + Send + Sync>(
-        &'b mut self,
-        ptr: &'b JsonPointer<S, V>,
-        lock: LockType,
-    ) -> BoxFuture<'b, ()> {
-        SubTransaction::lock(self, ptr, lock).boxed()
-    }
-    fn get<
-        'b,
-        T: for<'de> Deserialize<'de> + 'b,
-        S: AsRef<str> + Clone + Send + Sync + 'b,
-        V: SegList + Clone + Send + Sync + 'b,
-    >(
-        &'b mut self,
-        ptr: &'b JsonPointer<S, V>,
-        lock: LockType,
-    ) -> BoxFuture<'b, Result<T, Error>> {
-        SubTransaction::get(self, ptr, lock).boxed()
-    }
-    fn put<
-        'b,
-        T: Serialize + Send + Sync + 'b,
-        S: AsRef<str> + Send + Sync + 'b,
-        V: SegList + Send + Sync + 'b,
-    >(
-        &'b mut self,
-        ptr: &'b JsonPointer<S, V>,
-        value: &'b T,
-    ) -> BoxFuture<'b, Result<(), Error>> {
-        SubTransaction::put(self, ptr, value).boxed()
-    }
 }