From 36ae79f1df297289e1aa4a7e0ae96473c445bdfd Mon Sep 17 00:00:00 2001
From: William Chong <william-chong@outlook.com>
Date: Wed, 6 May 2026 11:52:13 +0400
Subject: [PATCH] feat: support projection v2 engine

---
 kurrentdb/protos/projections.proto            |  1 +
 .../src/event_store/generated/projections.rs  |  2 ++
 kurrentdb/src/options/projections.rs          | 27 +++++++++++++++++++
 kurrentdb/src/projection_client.rs            |  1 +
 4 files changed, 31 insertions(+)

diff --git a/kurrentdb/protos/projections.proto b/kurrentdb/protos/projections.proto
index 1fe8f367..2341246f 100644
--- a/kurrentdb/protos/projections.proto
+++ b/kurrentdb/protos/projections.proto
@@ -28,6 +28,7 @@ message CreateReq {
 			Continuous continuous = 3;
 		}
 		string query = 4;
+		int32 engine_version = 5;
 
 		message Transient {
 			string name = 1;
diff --git a/kurrentdb/src/event_store/generated/projections.rs b/kurrentdb/src/event_store/generated/projections.rs
index cbef0daa..2c0500f8 100644
--- a/kurrentdb/src/event_store/generated/projections.rs
+++ b/kurrentdb/src/event_store/generated/projections.rs
@@ -10,6 +10,8 @@ pub mod create_req {
     pub struct Options {
         #[prost(string, tag = "4")]
         pub query: ::prost::alloc::string::String,
+        #[prost(int32, tag = "5")]
+        pub engine_version: i32,
         #[prost(oneof = "options::Mode", tags = "1, 2, 3")]
         pub mode: ::core::option::Option<options::Mode>,
     }
diff --git a/kurrentdb/src/options/projections.rs b/kurrentdb/src/options/projections.rs
index b2711ff6..cf84f394 100644
--- a/kurrentdb/src/options/projections.rs
+++ b/kurrentdb/src/options/projections.rs
@@ -1,10 +1,30 @@
 use kurrentdb_macros::options;
 
+/// Selects which projection engine the server should use when creating a
+/// continuous projection. `V1` is the default and is supported by every server
+/// version. `V2` requires a server that supports the next-generation engine.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+pub enum ProjectionEngineVersion {
+    #[default]
+    V1,
+    V2,
+}
+
+impl ProjectionEngineVersion {
+    pub(crate) fn as_i32(self) -> i32 {
+        match self {
+            ProjectionEngineVersion::V1 => 1,
+            ProjectionEngineVersion::V2 => 2,
+        }
+    }
+}
+
 options! {
     #[derive(Clone, Default)]
     pub struct CreateProjectionOptions {
         pub(crate) track_emitted_streams: bool,
         pub(crate) emit: bool,
+        pub(crate) engine_version: ProjectionEngineVersion,
     }
 }
 
@@ -23,6 +43,13 @@ impl CreateProjectionOptions {
     pub fn emit(self, emit: bool) -> Self {
         Self { emit, ..self }
     }
+
+    pub fn engine_version(self, engine_version: ProjectionEngineVersion) -> Self {
+        Self {
+            engine_version,
+            ..self
+        }
+    }
 }
 
 options! {
diff --git a/kurrentdb/src/projection_client.rs b/kurrentdb/src/projection_client.rs
index f9249cc7..501bf693 100644
--- a/kurrentdb/src/projection_client.rs
+++ b/kurrentdb/src/projection_client.rs
@@ -74,6 +74,7 @@ impl ProjectionClient {
             options,
             projections::create_req::Options {
                 query: query.clone(),
+                engine_version: options.engine_version.as_i32(),
                 mode: Some(projections::create_req::options::Mode::Continuous(
                     projections::create_req::options::Continuous {
                         name: name.as_ref().to_string(),