Proto DataStore in Android

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("[email protected]")

.setId(20)

.setName("Ayushi")

.build()

}

To learn more about datastore, check following link : DataStore

Hopefully, this blog will be helpful for you.

ayushi agarwal 27 January 2021

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