*ngIf with button, disabled or not disabled Angular 9

Issue

I have two drop downs that are parameters for a function that is called on the Retrieve button click. What I want to happen is when both drop downs do not have data selected, the Retrieve button is disabled. If both drop downs have data then I want the button to act normally. Here is my current html:

<div class="dropdown">
  <div class="input-group">
    <h4 class="sessionText">Session: </h4>
    <select [(ngModel)]='sessionReportFilter.sessionName'
            class="custom-select form-control-sm"
            (change)='sessionDataChange($event)'
            id="inputGroupSelect01">
      <option [value]="null">Select session...</option>
      <option *ngFor="let session of sessionData" [value]='session.sessionName'>
        {{session.sessionName}}
      </option>
    </select>
  </div>

  <div class="input-group">
    <h4 class="reportText">Report Date: </h4>
    <select [(ngModel)]='sessionReportFilter.fileName' *ngIf='currentSession' class="custom-select form-control-sm" id="inputGroupSelect01">
      <option [value]="null">Select report...</option>
      <option *ngFor="let report of currentSession.reportFiles"
              [value]="report">
        {{report}}
      </option>
    </select>
    <select *ngIf="currentSession === null" class="custom-select form-control-sm" id="inputGroupSelect01"></select>
  </div>
  <div>
    <button type="button" class="btn btn-primary" disabled="disabled">Retrieve</button>
    <button type="button" class="btn btn-primary" (click)="orderExceptionReportData()">Retrieve</button>
  </div>
</div>

How can I achieve the desired results?

Solution

[disabled]="!sessionReportFilter.fileName && !sessionReportFilter.sessionName"

Replace that where you want the disabled button when at least one dropdown don't have a value,

so

<button type="button" class="btn btn-primary" disabled="disabled">Retrieve</button>

would be

<button type="button" class="btn btn-primary" [disabled]="!sessionReportFilter.fileName && !sessionReportFilter.sessionName">Retrieve</button>

Answered By - Alejandro Camba