NextJS中MongoDB模型在API路由报错，前端调用正常求排查

从前端调用操作MongoDB模型的Server Action完全正常，但通过API路由调用同一个Server Action时出现错误，错误信息如下：

database/question.model.ts (49:0) @
Cannot read properties of undefined (reading 'Question')

报错对应代码行：const Question = models.Question || model("Question", QuestionSchema);

相关代码 #

1. MongoDB模型代码 #

import { Schema, models, model, Document } from "mongoose";

export interface IQuestion extends Document {
  quetions: string;
  author: Schema.Types.ObjectId[];
  answers: string;
}

const QuestionSchema = new Schema({
  questions: { type: String, required: true },
  author: { type: Schema.Types.ObjectId, ref: "User" },
  answers: { type: String, required: false },
});

const Question = models.Question || model("Question", QuestionSchema);

export default Question;

2. Server Action代码 #

export async function getQuestionsCount(params: GetCountByAuthorParams) {
  try {
    connectToDatabase();

    const { author } = params;

    console.log("Author", author);

    const query: FilterQuery<typeof Question> = {
      author,
    };

    const totalQuestions = await Question.countDocuments(query);
    return totalQuestions;
  } catch (error) {
    console.log(error);
    throw error;
  }
}

3. 前端调用（正常工作） #

const params = {
  author: userIdRef.current!,
};

const total = await getQuestionsCount(params);
console.log("Total Count", total);

4. API路由调用（无法工作） #

const params: GetCountByAuthorParams = {
  author: authorID!,
};

const total = await getQuestionsCount(params);
console.log("Total Count", total);

问题原因与解决方案 #

核心原因 #

问题出在数据库连接的时序上：你在Server Action里调用connectToDatabase()时没有用await等待连接完成，就直接去访问Mongoose的models对象了。

前端调用Server Action时，Next.js的执行机制可能隐性处理了连接等待的逻辑；但API路由是独立的请求处理流程，没有这个隐性处理，导致模型加载时models对象还未被Mongoose初始化，所以会报Cannot read properties of undefined (reading 'Question')。

修复步骤 #

1. 修改Server Action，等待数据库连接完成
   在connectToDatabase()前添加await，确保连接成功后再操作模型：

   export async function getQuestionsCount(params: GetCountByAuthorParams) {
     try {
       // 关键：添加await等待连接完成
       await connectToDatabase();
   
       const { author } = params;
       console.log("Author", author);
   
       const query: FilterQuery<typeof Question> = { author };
       const totalQuestions = await Question.countDocuments(query);
       return totalQuestions;
     } catch (error) {
       console.log(error);
       throw error;
     }
   }
   

2. 确保数据库连接函数是单例模式
   检查你的connectToDatabase()实现，要避免重复创建连接，比如可以这样写：

   import mongoose from "mongoose";
   
   let isConnected = false;
   
   export async function connectToDatabase() {
     if (isConnected) {
       return;
     }
   
     try {
       await mongoose.connect(process.env.MONGODB_URI!);
       isConnected = true;
       console.log("数据库连接成功");
     } catch (error) {
       console.error("数据库连接失败:", error);
       throw error;
     }
   }
   

3. 额外修正：模型接口字段拼写错误
   你的IQuestion接口里的quetions是拼写错误，应该改成questions，和Schema中的字段保持一致，避免后续数据操作出现问题：

   export interface IQuestion extends Document {
     questions: string; // 修正拼写
     author: Schema.Types.ObjectId[];
     answers: string;
   }
   

内容的提问来源于stack exchange，提问作者Powerup California