From 3b7cfe40c506f69423eece614e37798b57ca193b Mon Sep 17 00:00:00 2001
From: Piyush Chauhan <42397980+pyshx@users.noreply.github.com>
Date: Thu, 25 Jul 2024 18:57:11 +0530
Subject: [PATCH] feat(mongox): support nearest read preference (#42)

* feat(mongox): support nearest read preference

* add read pref to client
---
 mongox/client.go      | 8 +++++++-
 mongox/transaction.go | 9 ++++++++-
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/mongox/client.go b/mongox/client.go
index 8b284c85..8b3f7516 100644
--- a/mongox/client.go
+++ b/mongox/client.go
@@ -6,6 +6,8 @@ import (
 
 	"github.com/reearth/reearthx/usecasex"
 	"go.mongodb.org/mongo-driver/mongo"
+	"go.mongodb.org/mongo-driver/mongo/options"
+	"go.mongodb.org/mongo-driver/mongo/readpref"
 	"go.mongodb.org/mongo-driver/x/mongo/driver/connstring"
 )
 
@@ -15,8 +17,12 @@ type Client struct {
 }
 
 func NewClient(database string, c *mongo.Client) *Client {
+	rp := readpref.Nearest()
+	
+	sessionOpts := options.Database().SetReadPreference(rp)
+
 	return &Client{
-		db:          c.Database(database),
+		db:          c.Database(database, sessionOpts),
 		transaction: &usecasex.NopTransaction{},
 	}
 }
diff --git a/mongox/transaction.go b/mongox/transaction.go
index 4f926f1e..d9f9e952 100644
--- a/mongox/transaction.go
+++ b/mongox/transaction.go
@@ -7,6 +7,7 @@ import (
 	"github.com/reearth/reearthx/usecasex"
 	"go.mongodb.org/mongo-driver/mongo"
 	"go.mongodb.org/mongo-driver/mongo/options"
+	"go.mongodb.org/mongo-driver/mongo/readpref"
 	"go.mongodb.org/mongo-driver/x/mongo/driver"
 )
 
@@ -23,7 +24,13 @@ func NewTransaction(client *mongo.Client) *Transaction {
 }
 
 func (t *Transaction) Begin(ctx context.Context) (usecasex.Tx, error) {
-	s, err := t.client.StartSession(options.Session())
+	// Set the read preference to Nearest
+	rp := readpref.Nearest()
+	
+	// Create session options with the Nearest read preference
+	sessionOpts := options.Session().SetDefaultReadPreference(rp)
+
+	s, err := t.client.StartSession(sessionOpts)
 	if err != nil {
 		return nil, err
 	}