Android Room持久性库-如何插入具有List对象字段的类 [英] Android room persistent library - how to insert class that has a List object field

问题描述

在 Android会议室持久性库中，如何将整个Model对象插入本身具有另一个列表的表.

In Android room persistent library how to insert entire Model object into table which has in itself another list.

让我告诉你我的意思:

@Entity(tableName = TABLE_NAME)
public class CountryModel {

    public static final String TABLE_NAME = "Countries";

    @PrimaryKey
    private int idCountry;

    private List<CountryLang> countryLang = null;

    public int getIdCountry() {
        return idCountry;
    }

    public void setIdCountry(int idCountry) {
        this.idCountry = idCountry;
    }

    public String getIsoCode() {
        return isoCode;
    }

    public void setIsoCode(String isoCode) {
        this.isoCode = isoCode;
    }

    /** 
        here i am providing a list of coutry information how to insert 
        this into db along with CountryModel at same time 
    **/
    public List<CountryLang> getCountryLang() {
        return countryLang;
    }

    public void setCountryLang(List<CountryLang> countryLang) {
        this.countryLang = countryLang;
    }
}

我的DAO看起来像这样:

my DAO looks like this:

@Dao
public interface CountriesDao{

    @Query("SELECT * FROM " + CountryModel.TABLE_NAME +" WHERE isoCode =:iso_code LIMIT 1")
    LiveData<List<CountryModel>> getCountry(String iso_code);

    @Query("SELECT * FROM " + CountryModel.TABLE_NAME )
    LiveData<List<CountryModel>> getAllCountriesInfo();

    @Insert(onConflict = REPLACE)
    Long[] addCountries(List<CountryModel> countryModel);

    @Delete
    void deleteCountry(CountryModel... countryModel);

    @Update(onConflict = REPLACE)
    void updateEvent(CountryModel... countryModel);
}

当我调用database.CountriesDao().addCountries(countryModel);时，出现以下Room db编译错误: 错误:(58，31)错误:无法弄清楚如何将该字段保存到数据库中.您可以考虑为其添加类型转换器.

When i call database.CountriesDao().addCountries(countryModel); i get the following room db compile error: Error:(58, 31) error: Cannot figure out how to save this field into database. You can consider adding a type converter for it.

是否应该有另一个名为CountryLang的表?如果可以的话，如何告诉房间在插入语句上将它们连接起来?

should there be another table called CountryLang ? and if so how to tell room to connect them on insert statement ?

CountryLang对象本身如下所示:

The CountryLang object itself looks like this:

public class CountryLang {


    private int idCountry;

    private int idLang;

    private String name;

    public int getIdCountry() {
        return idCountry;
    }

    public void setIdCountry(int idCountry) {
        this.idCountry = idCountry;
    }

    public int getIdLang() {
        return idLang;
    }

    public void setIdLang(int idLang) {
        this.idLang = idLang;
    }

    public String getName() {
        return name;
    }

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

}

响应如下:

"country_lang": [
      {
        "id_country": 2,
        "id_lang": 1,
        "name": "Austria"
      }
    ]

对于每个国家/地区来说，这里的内容不会多于一项.我不愿意在country_lang列表中仅对其中一项进行设计.因此，我可以为country_lang创建一个表，然后将其链接到CountryModel.但是如何?我可以使用外键吗?我希望我不必使用平面文件.所以你说我必须将其存储为json吗?是否建议不要暂时使用房间?改用什么?

For every country so its not going to be more then one item here. Im comfortable desgning it for just one item in the country_lang list. So i can just make a table for country_lang and then some how link it to CountryModel. but how ? can i use foreign key ? i was hoping i did not have to use a flat file. so your saying i have to store it as json ? Is it recommended not to use room for temporary ? what to use instead ?

推荐答案

正如Omkar所说，您不能.在这里，我根据文档描述了为什么应该始终使用@Ignore批注:

As Omkar said, you cannot. Here, I describe why you should always use @Ignore annotation according to the documentation: https://developer.android.com/training/data-storage/room/referencing-data.html#understand-no-object-references

您将在一个表中处理Country对象，以仅检索其能力的数据；语言对象将转到另一个表，但是您可以保留相同的Dao:

You will treat the Country object in a table to retrieve the data of its competence only; The Languages objects will go to another table but you can keep the same Dao:

• 国家和语言对象是独立的，只需在语言"实体(countryId，languageId)中定义带有更多字段的primaryKey即可.当活动线程是Worker线程时，可以将它们串联保存在Repository类中:两个对Dao的插入请求.
• 要加载Countrys对象，您需要有countryId.
• 要加载相关的Languages对象，您已经具有countryId，但是您需要先加载该国家/地区，然后再加载语言，以便可以在父对象中设置它们并仅返回父对象.
• 加载国家/地区时，您可以在Repository类中依次进行此操作，因此，您将同步加载国家/地区和语言，就像在服务器端一样！ (没有ORM库).

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