Mongoengine Read-Write Router

A MongoDB read-write separation solution for mongoengine ODM, inspired by the django-rw-router architecture.

This library routes write operations to the primary database and read operations to replica set members, with configurable consistency strategies.

Features

• Automatic read-write routing - Writes go to primary, reads go to replicas
• Multiple consistency strategies - random, transaction-aware, consistent hashing
• Read-after-write consistency - Ensures you see your own writes
• Request context tracking - Thread-safe context using contextvars
• Web framework integration - Middleware for FastAPI, Flask, and Django
• Force primary reads - Explicit control when you need fresh data
• Write operation tracking - Automatic context updates on writes

Installation

pip install mongoengine-rw-router

Configure 配置方式

支持三种配置方式，按场景选择：

方式 1：configure_from_url（单 URL，推荐）

适用于副本集单连接串（含 replicaSet、authSource、多节点、用户名密码）：

from mongoengine import Document, StringField
from mongoengine_rw_router import RwDocumentMixin, configure_from_url

# 阿里云 / 自建副本集等
host = "mongodb://root:xx@node1:3717,node2:3717/?replicaSet=mgset-xxx&authSource=admin"
configure_from_url(host=host, db="myapp")

class User(RwDocumentMixin, Document):
    name = StringField()
    meta = {"db_alias": "default"}

user = User.objects.first()  # 读从库
user.save()  # 写主库

方式 2：configure_from_hosts（主从分离 URL）

主库与从库使用不同连接串时：

from mongoengine_rw_router import configure_from_hosts

configure_from_hosts(
    primary_host="mongodb://primary:27017",
    replica_hosts=["mongodb://replica1:27017", "mongodb://replica2:27017"],
    db="myapp",
)

方式 3：configure（手动模式）

用户自行调用 mongoengine.connect()：

from mongoengine import connect
from pymongo.read_preferences import ReadPreference
from mongoengine_rw_router import configure

connect(db="myapp", alias="default", host="mongodb://primary:27017")
connect(db="myapp", alias="replica1", host="mongodb://replica1:27017",
        read_preference=ReadPreference.SECONDARY_PREFERRED)

configure(primary_alias="default", replica_aliases=["replica1"])

Strategy Options

一致性场景 (DDIA)

与 django-rw-router 一致，支持 DDIA 第四章复制滞后导致的四种读一致性问题：

配置示例

# Read Your Writes（推荐，默认）
configure(
    primary_alias="default",
    replica_aliases=["replica1", "replica2"],
    strategy="transaction_aware",
    read_after_write_consistency=True,
    transaction_read_primary=True,
)

# Monotonic Reads / Consistent Prefix（需中间件注入 user_id）
configure(
    strategy="consistent_hash",
    hash_virtual_nodes=40,
)
app.add_middleware(MongoRouterMiddleware, user_id_attr="user.id")

# Eventual Consistency
configure(strategy="random")

强制主库读

# 方式 1：primary_queryset
user = User.primary_queryset().first()

# 方式 2：force_primary 链式调用
user = User.objects.force_primary().first()

# 方式 3：force_primary 上下文
from mongoengine_rw_router import force_primary
with force_primary():
    user = User.objects.first()

License

MIT

Credits

Inspired by django-rw-router