如果对象是嵌套的，则不显示JSON值

Question

这是我的代码：

<tbody class="mat-color--white tdw-card-thin tdw-border-2">
            <tr class="tdw-hover-up-thin" *ngFor="let item of _mData | tdwSearchfilter: _mSearchField: _mSearchQuery | orderBy: order:reverse:'case-insensitive'; let iRow=index">
                <th *ngIf="_mIsCheckable" class="tdw--text-align-right sort-remove">
                    <mat-checkbox [(ngModel)]="_mIsCheckedList[i]" ></mat-checkbox>
                </th>
                <th class="tdw-bottom-line-light tdw-padding-v-16 tdw-font-14 tdw-font-open-sans tdw-font-normal mat-color-text--grey-800"
                    *ngFor="let prop of _mColumns">{{item[prop.key]}}</th>
                <th class=" tdw-bottom-line-light tdw-text-align-right" *ngIf="_mOptions">

                    <button mat-icon-button [matMenuTriggerFor]="optionMenu" (menuClosed)="onMenuClosed(iRow)">
                        <mat-icon>more_vert</mat-icon>
                    </button>
                </th>
            </tr>

        </tbody>

和Typescript文件将从服务器获取以下数据。

在服务器调用上分配这些值

this._mColumns = this.tempData.headers;//success.headers;
this._mData = this.tempData.dataList.content;//success.dataList.content;

后端数据：

tempData = {
    "headers": [
      {
        "label": "User name",
        "key": "userName"
      },
      {
        "label": "First name",
        "key": "userInfoDetails.firstName"
      },
      {
        "label": "Middle name",
        "key": "userInfoDetails.middleName"
      },
      {
        "label": "Last name",
        "key": "userInfoDetails.lastName"
      },
      {
        "label": "Gender",
        "key": "userInfoDetails.gender"
      },
      {
        "label": "Personal number",
        "key": "userInfoDetails.personalNumber"
      },
      {
        "label": "Email",
        "key": "userInfoDetails.emailAddress"
      },
      {
        "label": "Home country",
        "key": "userInfoDetails.homeCountry"
      },
      {
        "label": "Career Level",
        "key": "userInfoDetails.careerLevel"
      },
      {
        "label": "Career PathwayDesc",
        "key": "userInfoDetails.careerPathwayDesc"
      },
      {
        "label": "Business UnitCode",
        "key": "userInfoDetails.businessUnitCode"
      },
      {
        "label": "business UnitDescription",
        "key": "userInfoDetails.businessUnitDescription"
      },
      {
        "label": "Dept number",
        "key": "userInfoDetails.deptNumber"
      },
      {
        "label": "Dept name",
        "key": "userInfoDetails.deptName"
      },
      {
        "label": "Operation Code",
        "key": "userInfoDetails.operationCode"
      },
      {
        "label": "Operation Description",
        "key": "userInfoDetails.operationDescription"
      },
      {
        "label": "DateOf joining",
        "key": "userInfoDetails.dateOfJoining"
      },
      {
        "label": "Address",
        "key": "userInfoDetails.address"
      },
      {
        "label": "Is contract employee",
        "key": "userInfoDetails.isContractEmployee"
      },
      {
        "label": "State",
        "key": "userInfoDetails.state"
      },
      {
        "label": "Contact number",
        "key": "userInfoDetails.contactNumber"
      },
      {
        "label": "Site name",
        "key": "userInfoDetails.site.siteName"
      }],
    "dataList": {
      "content": [
        {
          "userName": "Syed",
          "userInfoDetails": {
            "id": 1,
            "firstName": "Syed", "middleName": "Akmal", "lastName": "Pasha",
            "gender": "male", "personalNumber": 9589489884, "emailAddress": "syed@gmail.com",
            "homeCountry": "India"
          }
        },
        {
          "userName": "Ryan",
          "userInfoDetails": {
            "id": 2,
            "firstName": "Ryan", "middleName": "Sheiq", "lastName": "Samar",
            "gender": "male", "personalNumber": 9589489848, "emailAddress": "syed@gmail.com",
            "homeCountry": "Dubai"
          }
        }
      ],
      "last": true,
      "totalPages": 1,
      "totalElements": 2,
      "size": 20,
      "number": 0,
      "first": true,
      "sort": null,
      "numberOfElements": 2
    }
  };

问题是它无法显示嵌套对象，如“userInfoDetails.firstName”，但它显示的是直接对象的内容，但不显示子对象的内容。