使用mongoose和node.js插入数据库时​​，服务器实例池被销毁错误

Question

我正在将一个名为“ Users”的文档插入到我的mongo集合中，但出现错误

 server instance pool was destroyed

在我的addUser Api函数中，首先，我通过电子邮件检查了重复的用户，然后获取了用户角色的标题（即，（管理员，超级管理员），然后是fetchRole我正在将用户对象插入user集合

这是我的Api功能代码

 export function registerUser(body, db) {
 return new Promise((resolve, reject) => {
 UserModel(db).then(({ User, mongoose }) => {
  if (User) {
    body.contact.email = body.contact.email.toLowerCase();
    User.find({ "contact.email": body.contact.email }, function (err, docs) 
    {
      if (docs.length <= 0) {
        genSalt(parseInt(config.app["password_saltRounds"], 10)).then(
          salt => {
            hash(body.password, salt).then(hash => {
              body.password = hash;
              getRoleBySlug(body.role, db).then(roleDetails => {
                if (roleDetails) {
                  body.role = roleDetails._id;
                  var user = new User(body);
                  user.save(function (err, data) {
                    // mongoose.connection.close();
                    if (!err) {
                      // mongoose.connection.close();
                      resolve({
                        success: true,
                        message: "User Added Successfully",
                        data
                      });
                    } else {
                      resolve({
                        success: false,
                        message: "Unable to add User",
                        data: err
                      });
                      console.log(err);
                    }
                  });
                } else {
                  // mongoose.connection.close();
                  resolve({
                    success: false,
                    message: "Unable to add User",
                    data: err
                  });
                  console.log(err);
                }
              });
            });
          }
        );
      } else {
        // mongoose.connection.close();
        resolve({
          success: false,
          message: "User with same email already exists",
          data: null
        });
      }
    });
  } else {
    // mongoose.connection.close();
    resolve({
      success: false,
      message: "Server not Responding",
      data: null
     });
    }
   });
   });
  }

我遇到这样的错误      server instance pool was destroyed

在解决响应之前，我用mongoose.connection.close();进行了尝试，但仍然收到相同的错误，这就是为什么我评论mongoose.connection.close();的原因。