From 3744982cd9d53c71aec182e254d1d5b143188f62 Mon Sep 17 00:00:00 2001
From: Nick Alexander <nalexander@mozilla.com>
Date: Wed, 2 May 2018 15:38:12 -0700
Subject: [PATCH] Add `last_tx_id`.

---
 src/conn.rs  | 16 ++++++++++++++++
 src/store.rs |  4 ++++
 2 files changed, 20 insertions(+)

diff --git a/src/conn.rs b/src/conn.rs
index eb54dbbf..bc351244 100644
--- a/src/conn.rs
+++ b/src/conn.rs
@@ -387,6 +387,11 @@ impl<'a, 'c> HasSchema for InProgress<'a, 'c> {
     }
 }
 
+impl<'a, 'c> InProgressRead<'a, 'c> {
+    pub fn last_tx_id(&self) -> Entid {
+        self.0.last_tx_id()
+    }
+}
 
 impl<'a, 'c> InProgress<'a, 'c> {
     pub fn builder(self) -> InProgressBuilder<'a, 'c> {
@@ -526,6 +531,10 @@ impl<'a, 'c> InProgress<'a, 'c> {
             },
         }
     }
+
+    pub fn last_tx_id(&self) -> Entid {
+        self.partition_map[":db.part/tx"].index - 1
+    }
 }
 
 struct InProgressTransactWatcher<'a, 'o> {
@@ -617,6 +626,13 @@ impl Conn {
         self.metadata.lock().unwrap().attribute_cache.clone()
     }
 
+    pub fn last_tx_id(&self) -> Entid {
+        // The mutex is taken during this entire method.
+        let metadata = self.metadata.lock().unwrap();
+
+        metadata.partition_map[":db.part/tx"].index - 1
+    }
+
     /// Query the Mentat store, using the given connection and the current metadata.
     pub fn q_once<T>(&self,
                      sqlite: &rusqlite::Connection,
diff --git a/src/store.rs b/src/store.rs
index 1614d0f5..e3b269e0 100644
--- a/src/store.rs
+++ b/src/store.rs
@@ -191,6 +191,10 @@ impl Store {
     pub fn unregister_observer(&mut self, key: &String) {
         self.conn.unregister_observer(key);
     }
+
+    pub fn last_tx_id(&self) -> Entid {
+        self.conn.last_tx_id()
+    }
 }
 
 impl Queryable for Store {