GreenDao

https://www.jianshu.com/p/53083f782ea2

简介

数据库存储数据基本上每个APP都有用到，GreenDAO 是一个将对象映射到 SQLite 数据库中的轻量且快速的 ORM 解决方案，至于用法这里不再多少，网上有很资料，这里主要说一下，利用GreenDao保存JavaBean类型或者List类型的数据。

举个栗子

{
     rating: {
     max: 10,
     average: 7.9,
     stars: "40",
     min: 0
     },
     genres: [
     "动作",
     "奇幻",
     "冒险"
     ],
     title: "海王",
     casts: [
     {
     alt: "https://movie.douban.com/celebrity/1022614/",
     avatars: {
     small: "http://img1.doubanio.com/view/celebrity/s_ratio_celebrity/public/p32853.webp",
     large: "http://img1.doubanio.com/view/celebrity/s_ratio_celebrity/public/p32853.webp",
     medium: "http://img1.doubanio.com/view/celebrity/s_ratio_celebrity/public/p32853.webp"
     },
     name: "杰森·莫玛",
     id: "1022614"
     },
     {
     alt: "https://movie.douban.com/celebrity/1044702/",
     avatars: {
     small: "http://img3.doubanio.com/view/celebrity/s_ratio_celebrity/public/p34697.webp",
     large: "http://img3.doubanio.com/view/celebrity/s_ratio_celebrity/public/p34697.webp",
     medium: "http://img3.doubanio.com/view/celebrity/s_ratio_celebrity/public/p34697.webp"
     },
     name: "艾梅柏·希尔德",
     id: "1044702"
     },
     {
     alt: "https://movie.douban.com/celebrity/1010539/",
     avatars: {
     small: "http://img3.doubanio.com/view/celebrity/s_ratio_celebrity/public/p9206.webp",
     large: "http://img3.doubanio.com/view/celebrity/s_ratio_celebrity/public/p9206.webp",
     medium: "http://img3.doubanio.com/view/celebrity/s_ratio_celebrity/public/p9206.webp"
     },
     name: "威廉·达福",
     id: "1010539"
     }
     ],
     collect_count: 397576,
     original_title: "Aquaman",
     subtype: "movie",
     directors: [
     {
     alt: "https://movie.douban.com/celebrity/1032122/",
     avatars: {
     small: "http://img3.doubanio.com/view/celebrity/s_ratio_celebrity/public/p1509950363.8.webp",
     large: "http://img3.doubanio.com/view/celebrity/s_ratio_celebrity/public/p1509950363.8.webp",
     medium: "http://img3.doubanio.com/view/celebrity/s_ratio_celebrity/public/p1509950363.8.webp"
     },
     name: "温子仁",
     id: "1032122"
     }
     ],
     year: "2018",
     images: {
     small: "http://img3.doubanio.com/view/photo/s_ratio_poster/public/p2541280047.webp",
     large: "http://img3.doubanio.com/view/photo/s_ratio_poster/public/p2541280047.webp",
     medium: "http://img3.doubanio.com/view/photo/s_ratio_poster/public/p2541280047.webp"
     },
     alt: "https://movie.douban.com/subject/3878007/",
     id: "3878007"
     }

上面是豆瓣电影一个电影详情的数据，一般复杂，有一些套嵌JsonObject和JsonArray，数据库存储的都是基本类型，像上面那些objec或者array类型又改如何存到数据库中，这是个问题。GreenDao为我们提了一个解决方案，就是把这些数据统一都转成String类型，存到数据库中，用的时候再转成相应的类型。

具体分析

这里分别列数两个例子，一个是JsonObject， 一个是JsonArray的。
首先第一个字段rating，电影的评分，返回的是一个JsonObject，写出它的JavaBean

package com.zs.project.bean.movie;

import java.io.Serializable;

/**
 * Created by zs
 * Date：2018年 01月 17日
 * Time：15:20
 * —————————————————————————————————————
 * About: 电影评分
 * —————————————————————————————————————
 */
public class MovieRating implements Serializable {

    private int max;
    private float average;
    private int stars;
    private int min;

    public int getMax() {
        return max;
    }

    public void setMax(int max) {
        this.max = max;
    }

    public float getAverage() {
        return average;
    }

    public void setAverage(float average) {
        this.average = average;
    }

    public int getStars() {
        return stars;
    }

    public void setStars(int stars) {
        this.stars = stars;
    }

    public int getMin() {
        return min;
    }

    public void setMin(int min) {
        this.min = min;
    }

    @Override
    public String toString() {
        return "MovieRating{" +
                "max=" + max +
                ", average=" + average +
                ", stars=" + stars +
                ", min=" + min +
                '}';
    }
}

然后，写它的转换类MovieRatingConvert， 这里是用到的fastJson解析的，用Gson当然也是可以的，这个转换类实现的PropertyConverter接口，里面有两个方法，很好理解，String转JavaBean 和JavaBean转String。

package com.zs.project.greendao.convert;

import com.alibaba.fastjson.JSON;
import com.zs.project.bean.movie.MovieRating;

import org.greenrobot.greendao.converter.PropertyConverter;

/**
 * Created by zs
 * Date：2018年 12月 10日
 * Time：17:05
 * —————————————————————————————————————
 * About: 评分
 * —————————————————————————————————————
 */
public class MovieRatingConvert implements PropertyConverter<MovieRating, String>{

    @Override
    public MovieRating convertToEntityProperty(String databaseValue) {
        return JSON.parseObject(databaseValue , MovieRating.class);
    }

    @Override
    public String convertToDatabaseValue(MovieRating entityProperty) {
        return JSON.toJSONString(entityProperty);
    }
}

下面是电影的主演casts字段，返回的是一个JsonArray,同样是写它的JavaBean和转换类MovieCastsConvert

package com.zs.project.bean.movie;

import java.io.Serializable;

/**
 * Created by zs
 * Date：2018年 01月 17日
 * Time：15:17
 * —————————————————————————————————————
 * About: 主演 | 导演
 * —————————————————————————————————————
 */

public class MovieCasts implements Serializable{

    private String alt;
    private MovieImages avatars;
    private String name;
    private String id;

    public String getAlt() {
        return alt;
    }

    public void setAlt(String alt) {
        this.alt = alt;
    }

    public MovieImages getAvatars() {
        return avatars;
    }

    public void setAvatars(MovieImages avatars) {
        this.avatars = avatars;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    @Override
    public String toString() {
        return "MovieCasts{" +
                "alt='" + alt + '\'' +
                ", avatars=" + avatars +
                ", name='" + name + '\'' +
                ", id='" + id + '\'' +
                '}';
    }
}

package com.zs.project.greendao.convert;

import com.alibaba.fastjson.JSON;
import com.zs.project.bean.movie.MovieCasts;

import org.greenrobot.greendao.converter.PropertyConverter;

import java.util.List;

/**
 * Created by zs
 * Date：2018年 12月 10日
 * Time：17:07
 * —————————————————————————————————————
 * About:
 * —————————————————————————————————————
 */
public class MovieCastsConvert implements PropertyConverter<List<MovieCasts>, String>{

    @Override
    public List<MovieCasts> convertToEntityProperty(String databaseValue) {
        return JSON.parseArray(databaseValue , MovieCasts.class);
    }

    @Override
    public String convertToDatabaseValue(List<MovieCasts> entityProperty) {
        return JSON.toJSONString(entityProperty);
    }
}

这些都写完了，就是把他们都用在整个详情的Bean里面了。

@Id(autoincrement = true)
    private Long id;
    private String title;
    @Convert(converter = MovieRatingConvert.class , columnType = String.class)
    private MovieRating rating;
    private String year;
    @Convert(converter = MovieImagesConvert.class , columnType = String.class)
    private MovieImages images;
    private String alt;
    private String mobile_url;
    private String share_url;
    private String schedule_url;
    private String collect_count;
    private String comments_count;
    private String ratings_count;
    private String original_title;
    private String summary;
    @Convert(converter = StringConvert.class , columnType = String.class)
    private List<String> countries;
    @Convert(converter = StringConvert.class , columnType = String.class)
    private List<String> genres;
    @Convert(converter = StringConvert.class , columnType = String.class)
    private List<String> aka;
    @Convert(converter = MovieCastsConvert.class , columnType = String.class)
    private List<MovieCasts> casts;
    @Convert(converter = MovieCastsConvert.class , columnType = String.class)
    private List<MovieCasts> directors;

@Convert(converter = MovieRatingConvert.class , columnType = String.class)
    private MovieRating rating;
@Convert(converter = MovieCastsConvert.class , columnType = String.class)
    private List<MovieCasts> casts;

用到了这个Convert注解，表明它们的转换类，这样就可以转换成String保存到数据库中了