Proto DataStore in Android

Ayushi Agarwal

27 January 2021

Proto Datastore allows us to store custom type data. It uses protocol buffers to store data.

In share preference, we can only save data in key-value. DataStore allows us to store data in key-value pair and in form of object as well.

Proto DataStore is one way of DataStore to save data.

Please check my previous blog for datastore and preferences datastore : Preferences DataStore

Setup

Add Dependency

plugins {
    id "com.google.protobuf" version "0.8.12"
}
dependencies {
    implementation  "androidx.datastore:datastore-core:1.0.0-alpha06"
    implementation  "com.google.protobuf:protobuf-javalite:3.11.0"
}
protobuf {
    protoc {
        artifact = "com.google.protobuf:protoc:3.11.0"
    }

    generateProtoTasks {
        all().each { task ->
            task.builtins {
                java {
                    option 'lite'
                }
            }
        }
    }
}

plugins {

id "com.google.protobuf" version "0.8.12"

}

dependencies {

implementation "androidx.datastore:datastore-core:1.0.0-alpha06"

implementation "com.google.protobuf:protobuf-javalite:3.11.0"

}

protobuf {

protoc {

artifact = "com.google.protobuf:protoc:3.11.0"

}

generateProtoTasks {

all().each { task ->

task.builtins {

java {

option 'lite'

}

Define a schema

We have to create a predefined schema in our project. This schema defines the type of object which we wanna store in Proto DataStore.

Suppose, we wanna save user data. We need to create a .proto file in our project. Lets say User.proto. Directory : app/src/main/proto/

Schema :

syntax = "proto3";

option java_package = "com.example.datasource";
option java_multiple_files = true;

message User {
     string name = 1;
     int32 id = 2;
     string email = 3;
}

syntax = "proto3";

option java_package = "com.example.datasource";

option java_multiple_files = true;

message User {

string name = 1;

int32 id = 2;

string email = 3;

}

NOTE: After creating User.proto file, please rebuild your android project.

Create DataStore

Now, define a class which implements Serializer<T> , where T is the type defined in the proto file. This class will define how to read or write data.

object UserSerializer : Serializer<User> {
    override val defaultValue: User = User.getDefaultInstance()

    override fun readFrom(input: InputStream): User {
        try {
            return User.parseFrom(input)
        } catch (exception: InvalidProtocolBufferException) {
            throw CorruptionException("Cannot read proto.", exception)
        }
    }

    override fun writeTo(
        t: User,
        output: OutputStream
    ) = t.writeTo(output)
}

object UserSerializer : Serializer<User> {

override val defaultValue: User = User.getDefaultInstance()

override fun readFrom(input: InputStream): User {

try {

return User.parseFrom(input)

} catch (exception: InvalidProtocolBufferException) {

throw CorruptionException("Cannot read proto.", exception)

}

override fun writeTo(

t: User,

output: OutputStream

) = t.writeTo(output)

}

Use createDataStore() function for creating instance of DataStore.

val userDataStore: DataStore<User> = createDataStore(
        fileName = "user.pb",
        serializer = UserSerializer
    )

val userDataStore: DataStore<User> = createDataStore(

fileName = "user.pb",

serializer = UserSerializer

)

Read Data from DataStore

Get user id :

val userData: Flow<Int> = userDataStore.data
                .map { user ->
                    user.id
                }

val userData: Flow<Int> = userDataStore.data

.map { user ->

user.id

}

Get user name :

val userData: Flow<String> = userDataStore.data .map { user -> user.name }

1	val userData: Flow<String> = userDataStore.data .map { user -> user.name }

Write Data in DataStore

updateData method is used to save data in Proto DataStore.

    suspend fun writeData() {
        userDataStore.updateData { user ->
            user.toBuilder()
                .setEmail("test@demo.com")
                .setId(20)
                .setName("Ayushi")
                .build()
        }
    }

suspend fun writeData() {

userDataStore.updateData { user ->

user.toBuilder()

.setEmail("test@demo.com")

.setId(20)

.setName("Ayushi")

.build()

}

To learn more about datastore, check following link : DataStore

Hopefully, this blog will be helpful for you.