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CacheFirstFetchPolicy: go to the network after a cache miss only (#351)
* Add refetchPolicyCacheFirstWithWriteToCacheAsync test * Use SQL cache * Go to the network if there's a cache miss only - not if there are other exceptions.
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7 files changed

Lines changed: 209 additions & 6 deletions

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‎normalized-cache/src/commonMain/kotlin/com/apollographql/cache/normalized/FetchPolicyInterceptors.kt‎

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@@ -47,7 +47,7 @@ val DefaultFetchPolicyInterceptor = object : ApolloInterceptor {
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cacheResponse.newBuilder().isLast(request.onlyIfCached || cacheResponse.exception == null)
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.build(),
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)
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if (cacheResponse.exception == null) {
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if (cacheResponse.exception !is CacheMissException) {
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return@flow
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}
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}

‎tests/defer/src/commonTest/kotlin/test/DeferNormalizedCacheTest.kt‎

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@@ -7,7 +7,6 @@ import com.apollographql.apollo.api.Error
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import com.apollographql.apollo.api.Operation
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import com.apollographql.apollo.exception.ApolloException
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import com.apollographql.apollo.exception.ApolloGraphQLException
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import com.apollographql.apollo.exception.ApolloHttpException
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import com.apollographql.apollo.exception.ApolloNetworkException
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import com.apollographql.apollo.exception.CacheMissException
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import com.apollographql.apollo.network.NetworkTransport
@@ -454,13 +453,10 @@ class DeferNormalizedCacheTest {
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)
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assertResponseListEquals(networkExpected, networkActual)
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mockServer.enqueueError(statusCode = 500)
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// Because of the error we fallback to the network (which also fails)
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// The error was stored in the cache and is surfaced as an exception
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val exception = apolloClient.query(WithFragmentSpreadsQuery()).execute().exception
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check(exception is ApolloGraphQLException)
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assertIs<ApolloHttpException>(exception.suppressedExceptions.first())
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assertEquals("GraphQL error: 'Cannot resolve isColor'", exception.message)
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mockServer.awaitRequest()
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}
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@Test

‎tests/fetch-policy/build.gradle.kts‎

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@@ -0,0 +1,50 @@
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import com.apollographql.apollo.annotations.ApolloExperimental
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plugins {
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alias(libs.plugins.kotlin.multiplatform)
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id("com.apollographql.apollo")
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}
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kotlin {
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configureKmp(
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withJs = setOf(JsAndWasmEnvironment.Node),
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withWasm = emptySet(),
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withAndroid = false,
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withApple = AppleTargets.Host,
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)
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sourceSets {
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getByName("commonMain") {
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dependencies {
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implementation(libs.apollo.runtime)
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implementation("com.apollographql.cache:normalized-cache")
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}
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}
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getByName("commonTest") {
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dependencies {
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implementation("com.apollographql.cache:test-utils")
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implementation(libs.apollo.mockserver)
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implementation(libs.kotlin.test)
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implementation(libs.turbine)
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}
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}
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getByName("jvmTest") {
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dependencies {
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implementation(libs.slf4j.nop)
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}
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}
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}
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}
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apollo {
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service("service") {
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packageName.set("test")
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@OptIn(ApolloExperimental::class)
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plugin("com.apollographql.cache:normalized-cache-apollo-compiler-plugin") {
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argument("com.apollographql.cache.packageName", packageName.get())
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}
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}
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}

‎tests/fetch-policy/src/commonMain/graphql/extra.graphqls‎

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extend schema
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@link(
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url: "https://specs.apollo.dev/kotlin_labs/v0.3"
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)
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@link(
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url: "https://specs.apollo.dev/cache/v0.3",
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import: ["@typePolicy", "@cacheControl", "@cacheControlField"]
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)
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extend type User @typePolicy(keyFields: "id")

‎tests/fetch-policy/src/commonMain/graphql/operation.graphql‎

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query MeQuery {
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me {
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id
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firstName
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lastName
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}
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}

‎tests/fetch-policy/src/commonMain/graphql/schema.graphqls‎

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type Query {
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me: User!
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}
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type User {
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id: ID!
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firstName: String
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lastName: String
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email: String
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}

‎tests/fetch-policy/src/commonTest/kotlin/test/FetchPolicyTest.kt‎

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package test
2+
3+
import app.cash.turbine.test
4+
import app.cash.turbine.withTurbineTimeout
5+
import com.apollographql.apollo.ApolloClient
6+
import com.apollographql.apollo.api.Error
7+
import com.apollographql.apollo.exception.ApolloGraphQLException
8+
import com.apollographql.apollo.exception.CacheMissException
9+
import com.apollographql.cache.normalized.FetchPolicy.CacheFirst
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import com.apollographql.cache.normalized.api.CacheHeaders
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import com.apollographql.cache.normalized.api.NormalizedCache
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import com.apollographql.cache.normalized.api.NormalizedCacheFactory
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import com.apollographql.cache.normalized.api.Record
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import com.apollographql.cache.normalized.api.RecordMerger
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import com.apollographql.cache.normalized.isFromCache
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import com.apollographql.cache.normalized.memory.MemoryCacheFactory
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import com.apollographql.cache.normalized.refetchPolicy
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import com.apollographql.cache.normalized.testing.assertErrorsEquals
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import com.apollographql.cache.normalized.testing.runTest
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import com.apollographql.cache.normalized.watch
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import com.apollographql.mockserver.MockRequestBase
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import com.apollographql.mockserver.MockResponse
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import com.apollographql.mockserver.MockServer
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import com.apollographql.mockserver.MockServerHandler
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import kotlinx.coroutines.delay
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import okio.use
27+
import test.cache.Cache.cache
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import kotlin.random.Random
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import kotlin.test.Test
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import kotlin.test.assertFails
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import kotlin.test.assertFalse
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import kotlin.test.assertIs
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import kotlin.test.assertTrue
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import kotlin.time.Duration.Companion.milliseconds
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36+
class FetchPolicyTest {
37+
@Test
38+
fun writeToCacheAsyncWithRefetchPolicyCacheFirstAndServerErrors() = runTest {
39+
MockServer.Builder().handler(
40+
object : MockServerHandler {
41+
override fun handle(request: MockRequestBase): MockResponse {
42+
return MockResponse.Builder()
43+
.body(
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// language=JSON
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"""
46+
{
47+
"errors": [
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{
49+
"message": "Can't compute lastName",
50+
"path": [
51+
"me",
52+
"lastName"
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]
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}
55+
],
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"data": {
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"me": {
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"__typename": "User",
59+
"id": "1",
60+
"firstName": "${Random.nextInt()}",
61+
"lastName": null
62+
}
63+
}
64+
}
65+
""".trimIndent()
66+
)
67+
.build()
68+
}
69+
}
70+
).build().use { mockServer ->
71+
ApolloClient.Builder()
72+
.serverUrl(mockServer.url())
73+
.cache(AsyncCacheFactory(), writeToCacheAsynchronously = true)
74+
.build()
75+
.use { apolloClient ->
76+
apolloClient.query(MeQuery())
77+
.refetchPolicy(CacheFirst)
78+
.watch()
79+
.test {
80+
// 1. response from the cache (cache miss)
81+
val cacheResponse1 = awaitItem()
82+
assertTrue(cacheResponse1.isFromCache)
83+
assertIs<CacheMissException>(cacheResponse1.exception)
84+
85+
// 2. response from the network, with the error
86+
val networkResponse1 = awaitItem()
87+
assertFalse(networkResponse1.isFromCache)
88+
assertErrorsEquals(
89+
listOf(Error.Builder("Can't compute lastName").path(listOf("me", "lastName")).build()),
90+
networkResponse1.errors
91+
)
92+
93+
// 3. with writeToCacheAsynchronously, when the network response is written to the cache, the watcher gets notified with the cache response
94+
val cacheResponse2 = awaitItem()
95+
assertTrue(cacheResponse2.isFromCache)
96+
// GraphQL error is surfaced as an exception by default (serverErrorsAsException is true)
97+
assertIs<ApolloGraphQLException>(cacheResponse2.exception)
98+
99+
// That wasn't a cache miss: expect no more emissions
100+
withTurbineTimeout(200.milliseconds) {
101+
assertFails { awaitItem() }
102+
}
103+
104+
cancelAndIgnoreRemainingEvents()
105+
}
106+
}
107+
}
108+
}
109+
}
110+
111+
/**
112+
* A cache that simulates slow writes.
113+
* This removes flakiness by ensuring that when using `writeToCacheAsynchronously = true`, there is enough time to start observing the
114+
* cache, before writing happens.
115+
*/
116+
private fun AsyncCacheFactory(): NormalizedCacheFactory = object : NormalizedCacheFactory() {
117+
override fun create(): NormalizedCache {
118+
val wrapped = MemoryCacheFactory().create()
119+
return object : NormalizedCache by wrapped {
120+
override suspend fun merge(
121+
records: Collection<Record>,
122+
cacheHeaders: CacheHeaders,
123+
recordMerger: RecordMerger,
124+
): Set<String> {
125+
delay(100.milliseconds)
126+
return wrapped.merge(records, cacheHeaders, recordMerger)
127+
}
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}
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}
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}

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