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Caching your data graph Offline & Reactive apps with Apollo Kotlin

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Hello, World! @BoD @MartinBonnin apollographql/apollo-kotlin

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What is GraphQL? An open source language to describe and run your API

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What is GraphQL? ● Schema ○ Int, Float, String, Boolean ○ Objects, Interfaces ○ Lists ○ Nullability ● Introspection ● Deprecation (and experimental soon 🧪)

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APIs in a REST world

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https://apis.guru/graphql-voyager/

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How does it look in practice query UserQuery { user { id login } }

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How does it look in practice query UserQuery { user { id login avatar { small medium } } }

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How does it look in practice query UserQuery { user { id login name } } { "data": { "user": { "id": "42", "login": "BoD", "name": "Benoit Lubek" } } }

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How does it look in practice query UserQuery { user { id login name } } { "data": { "user": { "id": "42", "login": "BoD", "name": "Benoit Lubek" } } }

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How does it look in practice query UserQuery { user { id email login name } } { "data": { "user": { "id": "42", "email": "[email protected]", "login": "BoD", "name": "Benoit Lubek" } } }

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Caching entities

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That doesn’t work with partial entities query ViewerQuery { viewer { # Returns a User id email avatarUrl } } query UserQuery($id: String) { user(id: $id) { # Also a User id email login name } }

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We could cache the HTTP response { "data": { "viewer": { "id": "42", "email": "[email protected]", "avatarUrl": "http://…" } } } { "data": { "user": { "id": "42", "email": "[email protected]", "login": "BoD", "name": "Benoit Lubek" } } }

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Entering Cache normalization Response -> List A Record is a Map

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Cache normalization - Response { "data": { "user": { "id": "42", "email": "[email protected]", "login": "BoD", "name": "Benoit Lubek" } } }

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Cache normalization - Records { "data": { "user": CacheReference("42"), }, "42": { "id": "42", "email": "[email protected]", "login": "BoD", "name": "Benoit Lubek" } }

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Adding fields { "data": { "user": CacheReference("42"), }, "42": { "id": "42", "email": "[email protected]", "login": "BoD", "name": "Benoit Lubek", // New Record field "avatarUrl": "http://…" } }

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{ "data": { "user": CacheReference("42"), }, "42": { "id": "42", "email": "[email protected]", "login": "BoD", "name": "Benoit Lubek", // New Record field "avatarUrl": "http://…" } } Cache ids Ids!

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What if there’s no id? { "data": { "user": { "email": "[email protected]", "login": "BoD", "name": "Benoit Lubek" } } }

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The field path is used as id { "data": { "user": CacheReference("data.user"), }, "data.user": { "email": "[email protected]", "login": "BoD", "name": "Benoit Lubek" } }

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What if there are several paths? { "data": { "todo": [ { "title": "Write retrowave slides!", "checked": true, "user": { "login": "BoD", "avatarUrl": "https://" }, }, ], } }

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The field path is used as id { "data": { "user": CacheReference("data.user"), }, "data.user": { "email": "[email protected]", "login": "BoD", "name": "Benoit Lubek" }, }

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The field path is used as id { "data": { "user": CacheReference("data.user"), "todo": CacheReference("data.todo"), }, "data.user": { "email": "[email protected]", "login": "BoD", "name": "Benoit Lubek" }, "data.todo": { "title": "Write retrowave slides!", "checked": true, "user": CacheReference("data.todo.user") }, "data.todo[0].user": { "login": "Bod", "avatarUrl": "https///" } }

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The field path is used as id { "data": { "user": CacheReference("data.user"), "todo": CacheReference("data.todo"), }, "data.user": { "email": "[email protected]", "login": "BoD", "name": "Benoit Lubek" }, "data.todo": { "title": "Write retrowave slides!", "checked": true, "user": CacheReference("data.todo.user") }, "data.todo.user": { "login": "Bod", "avatarUrl": "https///" } } Duplication

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Always define your ids

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This is all typesafe { "data": { "user": CacheReference("42"), }, "42": { "id": "42", "email": "[email protected]", "login": "BoD", "name": "Benoit Lubek" } } Data( user=User( id=42, [email protected], login=BoD, name=Benoit Lubek ) )

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Apollo Kotlin

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Storage: in-memory or persistent val memoryCache = MemoryCacheFactory(maxSizeBytes = 5_000_000) val apolloClient: ApolloClient = ApolloClient.Builder() .serverUrl(SERVER_URL) .normalizedCache(memoryCache) .build()

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Storage: in-memory or persistent val sqlCache = SqlNormalizedCacheFactory(context, "app.db") val apolloClient: ApolloClient = ApolloClient.Builder() .serverUrl(SERVER_URL) .normalizedCache(sqlCache) .build()

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Storage: in-memory and persistent val memoryCache = MemoryCacheFactory(maxSizeBytes = 5_000_000) val sqlCache = SqlNormalizedCacheFactory(context, "app.db") val memoryThenSqlCache = memoryCache.chain(sqlCache) val apolloClient: ApolloClient = ApolloClient.Builder() .serverUrl(SERVER_URL) .normalizedCache(memoryThenSqlCache) .build()

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Watchers

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The cache updates after a mutation mutation { updateUser({ id: "42", status: "Au DevFest Lille 😃" }) { id status } }

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The cache updates after a mutation watch() // receives from network "En télétravail 🏡" // wait for cache updates mutate("Au DevFest Lille 😃") // receives from network "Au DevFest Lille 😃" // updates the cache "Au DevFest Lille 😃" Coroutine 1 Coroutine 2

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Single source of truth

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Conclusion ● Type-safe language + Tooling = 💜 ● Offline support is one line 😎 ● Don’t forget your ids!

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Where to go from there ● Apollo-Kotlin ○ #3566 (data age) ○ #3807 (pagination) ● Server side caching ○ @cacheControl ○ Automated Persisted Queries

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For inspiration 🎊 github.com/joreilly/Confetti/pull/44

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Questions?

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Declarative cache type User { id: ID! name: String! } type Query { user(id: ID!): User } extend type User @typePolicy(keyFields: "id") extend type Query @fieldPolicy(forField: "user", keyArgs: "id")

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It depends.

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Optimistic updates

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Schema # schema.graphqls type Speaker implements Node { id: ID! name: String! company: String session(name: String!): Session sessions(first: Int, after: ID, orderBy: SessionOrder): [Session!] }

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Life is hard!