Android room数据库封装

平常咱们使用数据库的时候，基本操作都差不太多，增，删，改，查，但如果操作不同的数据时，就需要写较多的重复的代码，仅仅是因为操作的类对象变化了。下面咱们就通过泛型去封装一层baseDao，减少后期的模板代码。

abstract class baseDao {
    
    @Insert(onConflict = OnConflictStrategy.REPLACe)
    abstract fun insert(obj: T): Long

    
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    abstract fun insert(vararg objs: T): LongArray?

    
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    abstract fun insert(personList: List): List

    
    @Delete
    abstract fun delete(obj: T)

    
    @Update
    abstract fun update(vararg obj: T): Int

    fun deleteAll(): Int {
        val query = SimpleSQLiteQuery(
            "delete from $tableName"
        )
        return doDeleteAll(query)
    }

    fun findAll(): List? {
        val query = SimpleSQLiteQuery(
            "select * from $tableName"
        )
        return doFindAll(query)
    }

    fun find(id: Long): T? {
        val query = SimpleSQLiteQuery(
            "select * from $tableName where id = ?", arrayOf(id)
        )
        return doFind(query)
    }

    
    fun deleteByParams(params: String, value: String): Int {
        val query = SimpleSQLiteQuery("delete from $tableName where $params='${value}'")
        Log.d("ez", "deleteByParams: ${"delete from $tableName where $params='${value}'"}")
        return doDeleteByParams(query)
    }

    
    fun doQueryByLimit(vararg string: String, limit: Int = 10, offset: Int = 0): List? {
        val query =
            SimpleSQLiteQuery("SELECT * FROM $tableName WHERe ${string[0]} = '${string[1]}' limit $limit offset $offset")
        return doQueryByLimit(query)
    }

    
    fun doQueryByOrder(vararg string: String, limit: Int = 10, offset: Int = 10): List? {
        val query =
            SimpleSQLiteQuery("SELECt * FROM $tableName ORDER BY ${string[0]} desc limit '${limit}' offset '${offset}'")
        return doQueryByLimit(query)
    }

      
    val tableName: String
        get() {
            val clazz = (javaClass.superclass.genericSuperclass as ParameterizedType)
                .actualTypeArguments[0] as Class<*>
            val tableName = clazz.simpleName
            Log.d("ez", "getTableName: -->$tableName")
            return tableName
        }

    @RawQuery
    protected abstract fun doFindAll(query: SupportSQLiteQuery?): List?

    @RawQuery
    protected abstract fun doFind(query: SupportSQLiteQuery?): T

    @RawQuery
    protected abstract fun doDeleteAll(query: SupportSQLiteQuery?): Int

    @RawQuery
    protected abstract fun doDeleteByParams(query: SupportSQLiteQuery?): Int

    @RawQuery
    protected abstract fun doQueryByLimit(query: SupportSQLiteQuery?): List?

    @RawQuery
    protected abstract fun doQueryByOrder(query: SupportSQLiteQuery?): List?
}

因为Room的Query注解需要一个常量，这里就无法通过泛型去解决，所以就使用了SupportSQLiteQuery类和@RawQuery注解，这样咱们就可以通过sql语句来封装一些通用的操作，就解决了Query注解无法直接使用泛型的问题，详细用法请看上面的方法。

@Entity
class Person {
    @PrimaryKey(autoGenerate = true)
    var id: Long?
    var bh: String 
    var name: String? = null
    var loginName: String? = null
    var feature: ByteArray? = null
    var isPolice: Boolean = false

    constructor(
        id: Long? = null,
        name: String?,
        feature: ByteArray? = null,
        bh: String,
        loginName: String? = null,
        isPolice: Boolean = false
    ) {
        this.id = id
        this.name = name
        this.feature = feature
        this.bh = bh
        this.loginName = loginName
        this.isPolice = isPolice
    }

    override fun toString(): String {
        return "Person(id=$id, bh=$bh, name=$name,loginName=$loginName, isPolice=$isPolice)"
    }
}

@Dao
abstract class StudentDao : baseDao() {

}

这里咱们只要去继承baseDao然后传入需要操作的对象类型即可，通用的操作已封装在上层，无需再重复写了

构建 RoomDatabase

@Database(entities = [Person::class],version = 1,exportSchema = false)
abstract class DBFactory :RoomDatabase(){

    abstract fun getStudent():StudentDao

    companion object{
        private const val DB_NAME = "DBFactory.db"
        @Volatile
        private var dbFactory:DBFactory?=null

        @Synchronized
        fun getInstance(context: Context):DBFactory{
            if (dbFactory == null) {
                dbFactory = create(context)
            }
            return dbFactory!!
        }

        fun create(context: Context):DBFactory{
            return Room.databaseBuilder(context,DBFactory::class.java, DB_NAME).build()
        }

    }
}