没有得到新记录的_id

Question

我有一个使用node，express和mongoose的api。当我使用Postman调用api时，返回模型中的_id值。当我使用基于angularjs和ionic的web应用程序调用api时，_id为null。两种情况下都会保存记录。

我尝试在angularjs服务中设置标头。如果获取所有记录，则ID返回。我试过从猫鼬模型和角度模型中设置和删除_id

// api method 
public save = async (req:Request, res:Response): Promise<any> => {
        let newDfr = new DfrModel(req.body);

        try {
            const insertDFR = await newDfr.save({ validateBeforeSave: false}); 

            if (!insertDFR) {
                return res.status(404).send({
                    success: false,
                    message: 'Error Saving DFR',
                    data: null
                  });
            }
            console.log (newDfr);
            res.status(200).send({
                success: true,
                data: insertDFR
              });

        } catch (err) {
            res.status(500).send({
                success: false,
                message: err.toString(),
                data: null
            });
        }
    }


// Service Method on Service Class 
 public saveDFR(dfrModel: DfrModel) {
    return this.httpClient.post(environment.apiURL + '/dfrs', dfrModel);
  }

// Method on component
  async onSaveForm() {
    if (this.form.value.dfrStatus == null) {
      this.form.value.dfrStatus = 'Open';
    }

    const loader = await this.loadingController.create({
      message: 'Saving DFR, one moment please.',
      animated: true
    }).then(loaderElement => {
      loaderElement.present();

      this.dfrService.saveDFR(this.form.value).subscribe( val => {
        loaderElement.remove();
        this.dfrService.showNotification('DFR Template Saved');
      }, error => {
        loaderElement.remove();
        this.showAlert('Error Saving DFR. Please ensure all fields are valid');
      });
    });
  }

//客户端模型

export class DfrModel {
    constructor (
        public _id: string,
        public projectName: string,
        public projectNumber: string,

    ){}


}