save button disable when all field empty using angular js

When the user did not enter any values, I need to disable my save button.

  <form name="user">  
    <p>User Name </p>
    <input type="text" ng-model="user.username"/>
    
    <p>City </p>
    <input type="text" ng-model="user.city"/>
    
    <p>Job </p>
    <input type="text" ng-model="user.job"/>
    
    <p>Auth Level</p>
    <select ng-model="user.level"> 
      <option value="">--Select--</option>
      <option value="1"> Level 01</option>
      <option value="2"> Level 02</option>
      <option value="3"> Level 03</option>
    </select>
    <a href=""  
      class="btn btn-primary btn-flat"
      ng-click="saveUser(user)"
      ng-disabled="">
      Save
    </a>
  </form>

If all form fields empty, i need to disable save button. How I do this

Answer

Try this:

 <form name="user">  
    <p>User Name </p>
    <input type="text" ng-model="user.username" />
    
    <p>City </p>
    <input type="text" ng-model="user.city" />
    
    <p>Job </p>
    <input type="text" ng-model="user.job" />
    
    <p>Auth Level</p>
    <select ng-model="user.level"> 
      <option value="">--Select--</option>
      <option value="1"> Level 01</option>
      <option value="2"> Level 02</option>
      <option value="3"> Level 03</option>
    </select>
    <button
      class="btn btn-primary btn-flat"
      ng-click="saveUser(user)"
      ng-disabled="!user.username && 
                   !user.city  && 
                   !user.job"
      >
      Save
    </button>
  </form>