已配置Auth的Amplify如何基于用户sub id实现DataStore选择性数据下载

实现逻辑 #

Amplify仅支持全局执行一次configure命令，不需要在初始化阶段就确定同步用的sub id值，利用同步表达式的惰性执行特性即可实现动态按登录用户同步数据：

1. 调整初始化阶段的同步表达式配置 #

将静态常量取值改为动态获取当前登录用户的sub id，不需要提前写死固定值：

/* 添加Amplify插件 */
Amplify.addPlugin(AWSApiPlugin())
Amplify.addPlugin(AWSCognitoAuthPlugin())

Amplify.addPlugin(AWSDataStorePlugin.builder().dataStoreConfiguration(
    DataStoreConfiguration.builder()
        .syncExpression(Rooms::class.java) { 
            val currentUserSub = Amplify.Auth.currentUser?.userId ?: ""
            Devices.SUB.ge(currentUserSub) 
        }
        .syncExpression(Scenes::class.java) { 
            val currentUserSub = Amplify.Auth.currentUser?.userId ?: ""
            Devices.SUB.ge(currentUserSub) 
        }
        .syncExpression(Devices::class.java) { 
            val currentUserSub = Amplify.Auth.currentUser?.userId ?: ""
            Devices.SUB.ge(currentUserSub) 
        }
        .syncExpression(Automations::class.java) { 
            val currentUserSub = Amplify.Auth.currentUser?.userId ?: ""
            Devices.SUB.ge(currentUserSub) 
        }
        .syncExpression(MasterNodes::class.java) { 
            val currentUserSub = Amplify.Auth.currentUser?.userId ?: ""
            Devices.SUB.ge(currentUserSub) 
        }
        .build()
).build())

Amplify.configure(applicationContext)

2. 登录成功后刷新DataStore同步 #

如果登录前已经启动过DataStore，登录完成后先清空本地缓存再重启DataStore即可触发新的同步规则生效：

/* 启动DataStore同步 */
Amplify.DataStore.clear(
    {
        Amplify.DataStore.start(
            { Log.i(Constants.TAG_AMPLIFY, "DataStore 启动完成") },
            { error -> Log.e(Constants.TAG_AMPLIFY, "DataStore 启动失败", error) }
        )
    },
    { error -> Log.e(Constants.TAG_AMPLIFY, "DataStore 缓存清空失败", error) }
)

说明 #

• 同步表达式仅在DataStore启动执行同步操作时才会计算内部取值，初始化configure阶段不会执行，无需在初始化时就确定sub id的具体值
• 无需重复执行Amplify的configure命令，所有动态业务逻辑可以放在同步表达式的闭包内实时计算

内容的提问来源于stack exchange，提问作者Zubair Akber