flutter floor数据库查询有结果，实体对象没有值

今天在做数据库查询时，能返回正确的查询条数和实体对象，但是实体对象里都是空值，最后发现是因为实体对象没有创建构造函数导致的，新建一个构造函数就完美解决。记录一下。
附上我的实体类对象代码：

import 'package:floor/floor.dart';

@entity
class Beacon {
  @PrimaryKey(autoGenerate: true)
  int? id;
  String? major;
  String? minor;
  double? dx;
  double? dy;
  String? name;
  String? floorName;
  bool? indoor = true;
  int? gid;
  int? userid;
  String? projectionId;
  String? floorid;
  // 是否有修改
  bool? modified = false;
  String? mapId;

  void clear() {
    major = '';
    minor = '';
    dx = 0.0;
    dy = 0.0;
    name = null;
    floorName = null;
    gid = 1;
    projectionId = null;
    floorid = null;
    modified = false;
  }

  Beacon(
      {this.id,
      this.major,
      this.minor,
      this.dx,
      this.dy,
      this.name,
      this.floorName,
      this.floorid,
      this.indoor,
      this.gid,
      this.userid,
      this.projectionId,
      this.modified,
      this.mapId});

  @override
  bool operator ==(other) {
    if (other is! Beacon) {
      return false;
    }
    final Beacon beacon = other;
    return beacon.major == this.major &&
        beacon.minor == this.minor &&
        beacon.dx == this.dx &&
        beacon.dy == this.dy &&
        this.name == beacon.name &&
        this.floorName == beacon.floorName &&
        this.indoor == beacon.indoor &&
        this.gid == beacon.gid &&
        this.floorid == beacon.floorid &&
        this.projectionId == beacon.projectionId;
  }

  factory Beacon.fromJson(Map json) {
    String? major = json['deviceAttributes']['major'] as String?;
    String? minor = json['deviceAttributes']['minor'] as String?;
    double dx = (json['deviceAttributes']['x'] as num).toDouble();
    double dy = (json['deviceAttributes']['y'] as num).toDouble();
    bool indoor =
        json['deviceAttributes']['place'] as String == '室内' ? true : false;
    String projectionId = json['proId'] as String;
    String mapId = json['mapId'] as String;
    int userid = json['userId'] as int;
    String name = json['deviceName'];
    int gid = json['level'] ?? 1;
    String floorid = json['floorId'] as String;
    bool modified = false;
    Beacon beacon = Beacon(
        gid: gid,
        major: major,
        minor: minor,
        dx: dx,
        dy: dy,
        indoor: indoor,
        projectionId: projectionId,
        mapId: mapId,
        userid: userid,
        name: name,
        floorid: floorid,
        modified: modified);

    return beacon;
  }
}