Android 使用 Room 在 SQLite 中保存复杂的 JSON 响应

我认为问题出在作为列表的列上.

您可以添加以下类，以便将列表嵌入到类中:-

data class StringList(
    val stringList: List<String>
)
data class PicEntityList(
    val picEntityList: List<PicEntity>
)

然后将100更改为使用上述列表，如下所示:

@Entity(tableName = "albums")
data class AlbumEntity(
    @PrimaryKey(autoGenerate = false)
    val id: String,
    val title: String,
    val createdBy: String,
    val enabled: Boolean,
    //val keywords: List<String>, // obstacle here
    val keywords: StringList, /// now not an obstacle
    //val pics: List<PicEntity> // obstacle here
    val emojis: PicEntityList// now not an obstacle
)

为了能够存储"复杂的"(单个对象)，您需要对其进行转换，以便一些TypeConverter，例如

class RoomTypeConverters{
    @TypeConverter
    fun convertStringListToJSON(stringList: StringList): String = Gson().toJson(stringList)
    @TypeConverter
    fun convertJSONToStringList(json: String): StringList = Gson().fromJson(json,StringList::class.java)
    @TypeConverter
    fun convertPicEntityListToJSON(picEntityList: PicEntityList): String = Gson().toJson(picEntityList)
    @TypeConverter
    fun convertJSONToPicEntityList(json: String): PicEntityList = Gson().fromJson(json,PicEntityList::class.java)
}

• 注意，这利用了依赖关系com.google.code.gson

然后，您需要有@TypeConverters注释来覆盖适当的范围(在@数据库级别是最大的范围).Note the plural rather than singular, they are different.

为了演示上述工作，使用@DAO:-注释的接口中的First个函数

@Dao
interface AlbumDao {
    @Insert(onConflict = OnConflictStrategy.IGNORE)
    fun insert(albumEntity: AlbumEntity): Long
    @Query("SELECT * FROM albums")
    fun getAllAlbums(): List<AlbumEntity>
}

Second@数据库注解类(请注意@TypeConverters注解):-

@TypeConverters(RoomTypeConverters::class)
@Database(entities = [AlbumEntity::class], exportSchema = false, version = 1)
abstract class TheDatabase: RoomDatabase() {
    abstract fun getAlbumDao(): AlbumDao

    companion object {
        @Volatile
        private var instance: TheDatabase?=null
        fun getInstance(context: Context): TheDatabase {
            if (instance==null) {
                instance = Room.databaseBuilder(context,TheDatabase::class.java,"album.db")
                    .allowMainThreadQueries()
                    .build()
            }
            return instance as TheDatabase
        }
    }
}

Third一些实际做某事的活动代码(插入一些相册，然后将提取的数据写入日志(log)):

class MainActivity : AppCompatActivity() {
    lateinit var db: TheDatabase
    lateinit var dao: AlbumDao
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        db = TheDatabase.getInstance(this)
        dao = db.getAlbumDao()

        dao.insert(AlbumEntity(
            "Album001", "The First Album","Fred",false,
            StringList(listOf("The","First","Album")),
            PicEntityList(
                listOf(
                    PicEntity("PE001", listOf("emoji1","emoji2","emoji3")),
                    PicEntity("PE002",listOf("emoji10")),
                    PicEntity("PE003", listOf("emoji20","emoji21"))
                ))
        ))
        dao.insert(AlbumEntity(
            "Album002","This is the Second Album","Mary", true,
            StringList(listOf("keya","keyb","keyc","keyd","keye")),
            PicEntityList(
                listOf(
                    PicEntity("PE011", listOf("emoji30","emoji31")),
                    PicEntity("PE012", listOf("emoji1","emoji10","emoji20","emoji30"))
            ))
        ))
        for (a in dao.getAllAlbums()) {
            logAlbum(a)
        }
    }

    fun logAlbum(albumEntity: AlbumEntity) {
        val keywords = StringBuilder()
        for(s in albumEntity.keywords.stringList) {
            keywords.append("\n\t$s")
        }
        val pelog = StringBuilder()
        for (pe in albumEntity.emojis.picEntityList) {
            pelog.append("\n\tURL is ${pe.picUrl}")
            for (emoji in pe.emojis) {
                pelog.append("\n\t\tEmoji is ${emoji}")
            }
        }
        Log.d(
            "ALBUMINFO",
            "Album id is ${albumEntity.id} " +
                    "Title is ${albumEntity.title} " +
                    "CreateBy ${albumEntity.createdBy} " +
                    "Enabled=${albumEntity.enabled}. " +
                    "It has ${albumEntity.keywords.stringList.size} keywords. " +
                    "They are $keywords\n. " +
                    "It has ${albumEntity.emojis.picEntityList.size} emojis. " +
                    "They are ${pelog}"
        )
    }
}

• 在主线程上运行，以方便和简洁

运行时，日志(log)包含:-

D/ALBUMINFO: Album id is Album001 Title is The First Album CreateBy Fred Enabled=false. It has 3 keywords. They are 
        The
        First
        Album
    . It has 3 emojis. They are 
        URL is PE001
            Emoji is emoji1
            Emoji is emoji2
            Emoji is emoji3
        URL is PE002
            Emoji is emoji10
        URL is PE003
            Emoji is emoji20
            Emoji is emoji21
            
            
D/ALBUMINFO: Album id is Album002 Title is This is the Second Album CreateBy Mary Enabled=true. It has 5 keywords. They are 
        keya
        keyb
        keyc
        keyd
        keye
    . It has 2 emojis. They are 
        URL is PE011
            Emoji is emoji30
            Emoji is emoji31
        URL is PE012
            Emoji is emoji1
            Emoji is emoji10
            Emoji is emoji20
            Emoji is emoji30

• 即两张专辑与适当的嵌入列表一起被提取.

唱片表本身(通过应用判断)包括:-

从数据库的Angular 来看，另一种更好的方法不是将列表作为单个值(字符串)嵌入，而是将列表作为相关表(具有一对多或多对多关系).