Firestore Rules utilities to reduce verbosity. Generator: https://scaffoldhub.io/firestore-rules

firestore.rules

service cloud.firestore {
  match /databases/{database}/documents {

    // START - Usage example

    match /people/{document=**} {
      function propertiesValid() {
        return request.resource.data.keys().hasAll(['name', 'birthdate', 'yearsOfExperience'])
          && request.resource.data.size() == 3
          && isString('name') && minlength('name', 3) && maxlength('name', 255)
          && isString('birthdate')
          && (isNull('yearsOfExperience') || (isNumber('yearsOfExperience')));
      }

      function propertiesNonChanged() {
        return !changed('name');
      }

      allow read: if isAuthenticated();
      allow create: if isAuthenticated()
        && propertiesValid();
      allow update: if isAuthenticated()
        && propertiesValid()
        && propertiesNonChanged();
      allow delete: if isAuthenticated();
    }

    match /projects/{document=**} {
      function propertiesValid() {
        return request.resource.data.keys().hasAll(['name', 'started', 'budget'])
          && request.resource.data.size() == 3
          && isString('name') && minlength('name', 3) && maxlength('name', 255)
          && isBoolean('started')
          && isNumber('budget') && min('budget', 0.01) && max('budget', 50000);
      }

      allow read: if isAuthenticated();
      allow create: if isAuthenticated()
        && propertiesValid();
      allow update: if isAuthenticated()
        && propertiesValid();
      allow delete: if isAuthenticated();
    }

    // END - Usage example

    function isNull(property) {
      return request.resource.data[property] == null;
    }

    function changed(property) {
      return request.resource.data[property] != resource.data[property];
    }

    function isList(property) {
      return request.resource.data[property] is list;
    }

    function isString(property) {
      return request.resource.data[property] is string;
    }

    function isNumber(property) {
      return request.resource.data[property] is number;
    }

    function isBoolean(property) {
      return request.resource.data[property] is bool;
    }

    function isMap(property) {
      return request.resource.data[property] is map;
    }

    function isTimestamp(property) {
      return request.resource.data[property] is timestamp;
    }

    function minSize(property, value) {
      return request.resource.data[property].size() >= value;
    }

    function maxSize(property, value) {
      return request.resource.data[property].size() <= value;
    }

    function maxlength(property, value) {
      return request.resource.data[property].size() <= value;
    }

    function minlength(property, value) {
      return request.resource.data[property].size() >= value;
    }

    function max(property, value) {
      return request.resource.data[property] <= value;
    }

    function min(property, value) {
      return request.resource.data[property] >= value;
    }

    function isCurrentUser(userId) {
      return isAuthenticated() && request.auth.uid == userId;
    }

    function isAuthenticated() {
      return request.auth != null;
    }
  }
}