Exercise: UserDetailsRepository
In the UserDetailsRepository class, implement the getUserDetails function, which return details of the current user. It should:
- Check if the user is available in the database. If so, it should return this data.
- If the user is not available in the database, it should asynchronously fetch the user details from the client, use them to create a
UserDetailsobject, and return it. - After fetching new user data, it should asynchronously save it in the database.
getUserDetailsfunction should be able to complete its execution without waiting for the data to be saved.
Starting code:
class UserDetailsRepository(
private val client: UserDataClient,
private val userDatabase: UserDetailsDatabase,
private val backgroundScope: CoroutineScope,
) {
suspend fun getUserDetails(): UserDetails {
TODO()
}
}
interface UserDataClient {
suspend fun getName(): String
suspend fun getFriends(): List<Friend>
suspend fun getProfile(): Profile
}
interface UserDetailsDatabase {
suspend fun load(): UserDetails?
suspend fun save(user: UserDetails)
}
data class UserDetails(
val name: String,
val friends: List<Friend>,
val profile: Profile
)
data class Friend(val id: String)
data class Profile(val description: String)
This problem can either be solved in the below playground or you can clone kotlin-exercises project and solve it locally. In the project, you can find code template for this exercise in coroutines/starting/UserDetailsRepository.kt. You can find there starting code and unit tests.
Once you are done with the exercise, you can check your solution here.
Playground
import kotlinx.coroutines.*
import kotlinx.coroutines.test.currentTime
import kotlinx.coroutines.test.runTest
import org.junit.Test
import kotlin.test.assertEquals
class UserDetailsRepository(
private val client: UserDataClient,
private val userDatabase: UserDetailsDatabase,
private val backgroundScope: CoroutineScope,
) {
suspend fun getUserDetails(): UserDetails {
TODO()
}
}
interface UserDataClient {
suspend fun getName(): String
suspend fun getFriends(): List<Friend>
suspend fun getProfile(): Profile
}
interface UserDetailsDatabase {
suspend fun load(): UserDetails?
suspend fun save(user: UserDetails)
}
data class UserDetails(
val name: String,
val friends: List<Friend>,
val profile: Profile
)
data class Friend(val id: String)
data class Profile(val description: String)
@Suppress("FunctionName")
class UserDetailsRepositoryTest {
@Test
fun `should fetch details asynchronously`() = runTest {
// given
val client = object : UserDataClient {
override suspend fun getName(): String {
delay(100)
return "Ben"
}
override suspend fun getFriends(): List<Friend> {
delay(200)
return listOf(Friend("friend-id-1"))
}
override suspend fun getProfile(): Profile {
delay(300)
return Profile("Example description")
}
}
val database = InMemoryDatabase()
val repo = UserDetailsRepository(client, database, backgroundScope)
// when
val details = repo.getUserDetails()
// then
assertEquals("Ben", details.name)
assertEquals("friend-id-1", details.friends.single().id)
assertEquals("Example description", details.profile.description)
assertEquals(300, currentTime)
}
@Test
fun `should save details to database asynchronously`() = runTest {
// given
val client = object : UserDataClient {
override suspend fun getName(): String {
delay(100)
return "Ben"
}
override suspend fun getFriends(): List<Friend> {
delay(100)
return listOf(Friend("friend-id-1"))
}
override suspend fun getProfile(): Profile {
delay(100)
return Profile("Example description")
}
}
val database = InMemoryDatabase(saveTime = 1_000)
val repo = UserDetailsRepository(client, database, backgroundScope)
// when
repo.getUserDetails()
// then
assertEquals(100, currentTime)
// when
backgroundScope.coroutineContext.job.children.forEach { it.join() }
// then
assertEquals(1_100, currentTime)
}
@Test
fun `should load from database`() = runTest {
// given
val database = InMemoryDatabase(loadTime = 10)
database.save(UserDetails("Ben", listOf(Friend("friend-id-1")), Profile("Example description")))
val client = object : UserDataClient {
override suspend fun getName(): String {
error("Should not be called")
}
override suspend fun getFriends(): List<Friend> {
error("Should not be called")
}
override suspend fun getProfile(): Profile {
error("Should not be called")
}
}
val repo = UserDetailsRepository(client, database, backgroundScope)
// when
val details = repo.getUserDetails()
// then
assertEquals("Ben", details.name)
assertEquals("friend-id-1", details.friends.single().id)
assertEquals("Example description", details.profile.description)
assertEquals(10, currentTime)
}
class InMemoryDatabase(
private val saveTime: Long = 0,
private val loadTime: Long = 0,
) : UserDetailsDatabase {
private var stored: UserDetails? = null
override suspend fun load(): UserDetails? {
delay(loadTime)
return stored
}
override suspend fun save(user: UserDetails) {
delay(saveTime)
stored = user
}
}
}
