解决Django多数据库/多Schema环境下外键迁移问题

# auth/models.py
import uuid
from django.db import models

class SupabaseUser(models.Model):
    id = models.UUIDField(
        primary_key=True,
        default=uuid.uuid4,
        verbose_name="User ID",
        help_text="Supabase managed user id",
        editable=False,
    )

    class Meta:
        managed = False  # 表由外部管理，Django不创建或修改
        db_table = "users" # 指向auth Schema下的users表

# myapp/models.py
from django.db import models
from auth.models import SupabaseUser

class MyModel(models.Model):
   user = models.ForeignKey(
        SupabaseUser,
        on_delete=models.CASCADE,
        verbose_name="Supabase User",
        help_text="Supabase user associated with the account",
        null=False,
    )
   # 其他字段

# settings.py
import dj_database_url

DATABASES = {
    "default": dj_database_url.config(conn_max_age=600), # 默认数据库连接
    "supabase_auth": dj_database_url.config(conn_max_age=600), # 专门用于Supabase auth Schema
}
DATABASES["supabase_auth"]["OPTIONS"] = {
    "options": "-c search_path=auth", # 指定search_path为auth
}

# myproject/routers.py 或其他位置
from django.db.models import Model
from django.db.models.options import Options

class ModelRouter:
    @staticmethod
    def db_for_read(model: Model, **kwargs):
        return ModelRouter._get_db_schema(model._meta)

    @staticmethod
    def db_for_write(model: Model, **kwargs):
        return ModelRouter._get_db_schema(model._meta)

    @staticmethod
    def allow_migrate(db, app_label, model: Model, model_name=None, **kwargs):
        # 允许所有迁移，或者根据需要进行更精细的控制
        # 对于auth应用，我们可能不希望Django尝试创建auth.models.SupabaseUser对应的表
        # 但对于外键引用，我们需要确保其能够被正确处理
        if app_label == "auth" and db == "supabase_auth":
            return False # 不允许Django为SupabaseUser模型创建表，因为它由Supabase管理
        if app_label == "auth" and db == "default":
            return False # 也不允许在default数据库中创建
        if app_label == "myapp" and db == "default":
            return True # myapp模型在default数据库中
        if app_label == "myapp" and db == "supabase_auth":
            return False # myapp模型不在supabase_auth数据库中
        return None # 让Django决定

    @staticmethod
    def _get_db_schema(options: Options) -> str:
        if options.app_label == "auth":
            return "supabase_auth"
        return "default"

# myapp/migrations/00XX_add_user_foreign_key.py (或现有迁移文件)
from django.db import migrations

class Migration(migrations.Migration):
    dependencies = [
        # 确保在执行此迁移之前，auth应用的相关模型（虽然managed=False，但为了依赖关系清晰）
        # 和myapp的其他迁移已完成
        ("auth", "0001_initial"), # 假设auth应用有一个初始迁移
        ("myapp", "0012_alter_mymodel_some_field"), # 替换为myapp的实际前一个迁移
    ]

    operations = [
        migrations.RunSQL(
            sql=(
                # 添加 user_id 列，类型为UUID
                "ALTER TABLE myapp_mymodel ADD COLUMN user_id UUID;",
                # 添加外键约束，明确引用 auth.users 表的 id 列
                "ALTER TABLE myapp_mymodel ADD CONSTRAINT fk_user_id FOREIGN KEY (user_id) REFERENCES auth.users (id) ON DELETE CASCADE;",
            ),
            reverse_sql=(
                # 撤销迁移时执行的SQL：删除外键约束和列
                "ALTER TABLE myapp_mymodel DROP CONSTRAINT fk_user_id;",
                "ALTER TABLE myapp_mymodel DROP COLUMN user_id;",
            ),
        ),
    ]