Android room数据库封装

朱雀 2022-09-12 08:49 235阅读 0赞

#### 一、背景 ####

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。

#### 二、封装 ####

abstract class BaseDao<T> { 
        /** * 添加单个对象 */
        @Insert(onConflict = OnConflictStrategy.REPLACE)
        abstract fun insert(obj: T): Long
    
        /** * 添加数组对象数据 */
        @Insert(onConflict = OnConflictStrategy.REPLACE)
        abstract fun insert(vararg objs: T): LongArray?
    
        /** * 添加对象集合 */
        @Insert(onConflict = OnConflictStrategy.REPLACE)
        abstract fun insert(personList: List<T>): List<Long>
    
        /** * 根据对象中的主键删除（主键是自动增长的，无需手动赋值） */
        @Delete
        abstract fun delete(obj: T)
    
        /** * 根据对象中的主键更新（主键是自动增长的，无需手动赋值） */
        @Update
        abstract fun update(vararg obj: T): Int
    
        fun deleteAll(): Int { 
            val query = SimpleSQLiteQuery(
                "delete from $tableName"
            )
            return doDeleteAll(query)
        }
    
        fun findAll(): List<T>? { 
            val query = SimpleSQLiteQuery(
                "select * from $tableName"
            )
            return doFindAll(query)
        }
    
        fun find(id: Long): T? { 
            val query = SimpleSQLiteQuery(
                "select * from $tableName where id = ?", arrayOf<Any>(id)
            )
            return doFind(query)
        }
    
        /** * [params] 列名 * [value] 列的值 */
        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)
        }
    
        /** * 分页查询，支持传入多个字段，但必须要按照顺序传入 * key = value，key = value 的形式，一一对应（可以使用 stringbuilder 去构造一下，这里就不演示了） */
        fun doQueryByLimit(vararg string: String, limit: Int = 10, offset: Int = 0): List<T>? { 
            val query =
                SimpleSQLiteQuery("SELECT * FROM $tableName WHERE ${string[0]} = '${string[1]}' limit $limit offset $offset")
            return doQueryByLimit(query)
        }
    
        /** * 降序分页查询 */
        fun doQueryByOrder(vararg string: String, limit: Int = 10, offset: Int = 10): List<T>? { 
            val query =
                SimpleSQLiteQuery("SELECT * FROM $tableName ORDER BY ${string[0]} desc limit '${limit}' offset '${offset}'")
            return doQueryByLimit(query)
        }
    
          /** * 获取表名 */
        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<T>?
    
        @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<T>?
    
        @RawQuery
        protected abstract fun doQueryByOrder(query: SupportSQLiteQuery?): List<T>?
    }

> 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。

#### 三、使用 ####

@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<Person>() { 
    
    }

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()
            }
    
        }
    }