使用greendao存储数据过程中，我们会遇到bean嵌套的情况，这种情况怎么处理呢？我们需要用到greendao提供的PropertyConverter来处理。

原始数据

我们假设我们存储对象是CacheBean，它有个成员变量叫SubCachedBean，代码如下：

@Entity
public class CachedBean {
    private int count;

    private SubCachedBean subCachedBean;

    public int getCount() {
        return count;
    }

    public void setCount(int count) {
        this.count = count;
    }

    public SubCachedBean getSubCachedBean() {
        return subCachedBean;
    }

    public void setSubCachedBean(SubCachedBean subCachedBean) {
        this.subCachedBean = subCachedBean;
    }

    @Override
    public String toString() {
        return "CachedBean{" +
                "count=" + count +
                ", subCachedBean=" + subCachedBean +
                '}';
    }
}

public class SubCachedBean {
    private String name;
    private String gender;

    public String getName() {
        return name;
    }

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

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    @Override
    public String toString() {
        return "SubCachedBean{" +
                "name='" + name + '\'' +
                ", gender='" + gender + '\'' +
                '}';
    }
}

此时我们只给CachedBean添加了@Entity注解，SubCachedBean的数据是无法存储的。

使用`PropertyConverter`进行转换

我们针对SubCachedBean类，创建一个对应的PropertyConverter，将其转换为String，具体如下：

public class SubCachedBeanConverter implements PropertyConverter<SubCachedBean, String> {
    @Override
    public SubCachedBean convertToEntityProperty(String databaseValue) {
        return JSON.parseObject(databaseValue, SubCachedBean.class);
    }

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

接着我们在引用SubCachedBean对象的地方，添加对应的注解即可，代码如下：

@Convert(converter = SubCachedBeanConverter.class, columnType = String.class)
private SubCachedBean subCachedBean;

同理，针对List类型的数据也一样，只需要替换下PropertyConverter后面的泛型参数即可。