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              Resources > Migration Guides

              10 minutes

              AssemblyScript Migration Guide

              Up until now, Subgraphs have been using one of the first versions of AssemblyScript⁠ (v0.6). Finally we’ve added support for the newest one available⁠ (v0.19.10)! 🎉

              That will enable Subgraph developers to use newer features of the AS language and standard library.

              This guide is applicable for anyone using graph-cli/graph-ts below version 0.22.0. If you’re already at a higher than (or equal) version to that, you’ve already been using version 0.19.10 of AssemblyScript 🙂

              Note: As of 0.24.0, graph-node can support both versions, depending on the apiVersion specified in the Subgraph manifest.

              Features

              New functionality

              • TypedArrays can now be built from ArrayBuffers by using the new wrap static method⁠ (v0.8.1⁠)
              • New standard library functions: String#toUpperCase, String#toLowerCase, String#localeCompareand TypedArray#set (v0.9.0⁠)
              • Added support for x instanceof GenericClass (v0.9.2⁠)
              • Added StaticArray<T>, a more efficient array variant (v0.9.3⁠)
              • Added Array<T>#flat (v0.10.0⁠)
              • Implemented radix argument on Number#toString (v0.10.1⁠)
              • Added support for separators in floating point literals (v0.13.7⁠)
              • Added support for first class functions (v0.14.0⁠)
              • Add builtins: i32/i64/f32/f64.add/sub/mul (v0.14.13⁠)
              • Implement Array/TypedArray/String#at (v0.18.2⁠)
              • Added support for template literal strings (v0.18.17⁠)
              • Add encodeURI(Component) and decodeURI(Component) (v0.18.27⁠)
              • Add toString, toDateString and toTimeString to Date (v0.18.29⁠)
              • Add toUTCString for Date (v0.18.30⁠)
              • Add nonnull/NonNullable builtin type (v0.19.2⁠)

              Optimizations

              • Math functions such as exp, exp2, log, log2 and pow have been replaced by faster variants (v0.9.0⁠)
              • Slightly optimize Math.mod (v0.17.1⁠)
              • Cache more field accesses in std Map and Set (v0.17.8⁠)
              • Optimize for powers of two in ipow32/64 (v0.18.2⁠)

              Other

              • The type of an array literal can now be inferred from its contents (v0.9.0⁠)
              • Updated stdlib to Unicode 13.0.0 (v0.10.0⁠)

              How to upgrade?

              1. Change your mappings apiVersion in subgraph.yaml to 0.0.9:
              1...2dataSources:3  ...4    mapping:5      ...6      apiVersion: 0.0.97      ...
              1. Update the graph-cli you’re using to the latest version by running:
              1# if you have it globally installed2npm install --global @graphprotocol/graph-cli@latest34# or in your subgraph if you have it as a dev dependency5npm install --save-dev @graphprotocol/graph-cli@latest
              1. Do the same for graph-ts, but instead of installing globally, save it in your main dependencies:
              1npm install --save @graphprotocol/graph-ts@latest
              1. Follow the rest of the guide to fix the language breaking changes.
              2. Run codegen and deploy again.

              Breaking changes

              Nullability

              On the older version of AssemblyScript, you could create code like this:

              1function load(): Value | null { ... }23let maybeValue = load();4maybeValue.aMethod();

              However on the newer version, because the value is nullable, it requires you to check, like this:

              1let maybeValue = load()23if (maybeValue) {4  maybeValue.aMethod() // `maybeValue` is not null anymore5}

              Or force it like this:

              1let maybeValue = load()! // breaks in runtime if value is null23maybeValue.aMethod()

              If you are unsure which to choose, we recommend always using the safe version. If the value doesn’t exist you might want to just do an early if statement with a return in you Subgraph handler.

              Variable Shadowing

              Before you could do variable shadowing⁠ and code like this would work:

              1let a = 102let b = 203let a = a + b

              However now this isn’t possible anymore, and the compiler returns this error:

              1ERROR TS2451: Cannot redeclare block-scoped variable 'a'23 let a = a + b;4 ~~~~~~~~~~~~~5in assembly/index.ts(4,3)

              You’ll need to rename your duplicate variables if you had variable shadowing.

              Null Comparisons

              By doing the upgrade on your Subgraph, sometimes you might get errors like these:

              1ERROR TS2322: Type '~lib/@graphprotocol/graph-ts/common/numbers/BigInt | null' is not assignable to type '~lib/@graphprotocol/graph-ts/common/numbers/BigInt'.2     if (decimals == null) {3                     ~~~~4 in src/mappings/file.ts(41,21)

              To solve you can simply change the if statement to something like this:

              1if (!decimals) {23  // or45  if (decimals === null) {

              The same applies if you’re doing != instead of ==.

              Casting

              The common way to do casting before was to just use the as keyword, like this:

              1let byteArray = new ByteArray(10)2let uint8Array = byteArray as Uint8Array // equivalent to: <Uint8Array>byteArray

              However this only works in two scenarios:

              • Primitive casting (between types such as u8, i32, bool; eg: let b: isize = 10; b as usize);
              • Upcasting on class inheritance (subclass → superclass)

              Examples:

              1// primitive casting2let a: usize = 103let b: isize = 54let c: usize = a + (b as usize)
              1// upcasting on class inheritance2class Bytes extends Uint8Array {}34let bytes = new Bytes(2)5// <Uint8Array>bytes // same as: bytes as Uint8Array

              There are two scenarios where you may want to cast, but using as/<T>var isn’t safe:

              • Downcasting on class inheritance (superclass → subclass)
              • Between two types that share a superclass
              1// downcasting on class inheritance2class Bytes extends Uint8Array {}34let uint8Array = new Uint8Array(2)5// <Bytes>uint8Array // breaks in runtime :(
              1// between two types that share a superclass2class Bytes extends Uint8Array {}3class ByteArray extends Uint8Array {}45let bytes = new Bytes(2)6// <ByteArray>bytes // breaks in runtime :(

              For those cases, you can use the changetype<T> function:

              1// downcasting on class inheritance2class Bytes extends Uint8Array {}34let uint8Array = new Uint8Array(2)5changetype<Bytes>(uint8Array) // works :)
              1// between two types that share a superclass2class Bytes extends Uint8Array {}3class ByteArray extends Uint8Array {}45let bytes = new Bytes(2)6changetype<ByteArray>(bytes) // works :)

              If you just want to remove nullability, you can keep using the as operator (or <T>variable), but make sure you know that value can’t be null, otherwise it will break.

              1// remove nullability2let previousBalance = AccountBalance.load(balanceId) // AccountBalance | null34if (previousBalance != null) {5  return previousBalance as AccountBalance // safe remove null6}78let newBalance = new AccountBalance(balanceId)

              For the nullability case we recommend taking a look at the nullability check feature⁠, it will make your code cleaner 🙂

              Also we’ve added a few more static methods in some types to ease casting, they are:

              • Bytes.fromByteArray
              • Bytes.fromUint8Array
              • BigInt.fromByteArray
              • ByteArray.fromBigInt

              Nullability check with property access

              To use the nullability check feature⁠ you can use either if statements or the ternary operator (? and :) like this:

              1let something: string | null = 'data'23let somethingOrElse = something ? something : 'else'45// or67let somethingOrElse89if (something) {10  somethingOrElse = something11} else {12  somethingOrElse = 'else'13}

              However that only works when you’re doing the if / ternary on a variable, not on a property access, like this:

              1class Container {2  data: string | null3}45let container = new Container()6container.data = 'data'78let somethingOrElse: string = container.data ? container.data : 'else' // doesn't compile

              Which outputs this error:

              1ERROR TS2322: Type '~lib/string/String | null' is not assignable to type '~lib/string/String'.23   let somethingOrElse: string = container.data ? container.data : "else";4                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

              To fix this issue, you can create a variable for that property access so that the compiler can do the nullability check magic:

              1class Container {2  data: string | null3}45let container = new Container()6container.data = 'data'78let data = container.data910let somethingOrElse: string = data ? data : 'else' // compiles just fine :)

              Operator overloading with property access

              If you try to sum (for example) a nullable type (from a property access) with a non nullable one, the AssemblyScript compiler instead of giving a compile time error warning that one of the values is nullable, it just compiles silently, giving chance for the code to break at runtime.

              1class BigInt extends Uint8Array {2  @operator('+')3  plus(other: BigInt): BigInt {4    // ...5  }6}78class Wrapper {9  public constructor(public n: BigInt | null) {}10}1112let x = BigInt.fromI32(2)13let y: BigInt | null = null1415x + y // give compile time error about nullability1617let wrapper = new Wrapper(y)1819wrapper.n = wrapper.n + x // doesn't give compile time errors as it should

              We’ve opened a issue on the AssemblyScript compiler for this, but for now if you do these kind of operations in your Subgraph mappings, you should change them to do a null check before it.

              1let wrapper = new Wrapper(y)23if (!wrapper.n) {4  wrapper.n = BigInt.fromI32(0)5}67wrapper.n = wrapper.n + x // now `n` is guaranteed to be a BigInt

              Value initialization

              If you have any code like this:

              1var value: Type // null2value.x = 103value.y = 'content'

              It will compile but break at runtime, that happens because the value hasn’t been initialized, so make sure your Subgraph has initialized their values, like this:

              1var value = new Type() // initialized2value.x = 103value.y = 'content'

              Also if you have nullable properties in a GraphQL entity, like this:

              1type Total @entity {2  id: Bytes!3  amount: BigInt4}

              And you have code similar to this:

              1let total = Total.load('latest')23if (total === null) {4  total = new Total('latest')5}67total.amount = total.amount + BigInt.fromI32(1)

              You’ll need to make sure to initialize the total.amount value, because if you try to access like in the last line for the sum, it will crash. So you either initialize it first:

              1let total = Total.load('latest')23if (total === null) {4  total = new Total('latest')5  total.amount = BigInt.fromI32(0)6}78total.tokens = total.tokens + BigInt.fromI32(1)

              Or you can just change your GraphQL schema to not use a nullable type for this property, then we’ll initialize it as zero on the codegen step 😉

              1type Total @entity {2  id: Bytes!3  amount: BigInt!4}
              1let total = Total.load('latest')23if (total === null) {4  total = new Total('latest') // already initializes non-nullable properties5}67total.amount = total.amount + BigInt.fromI32(1)

              Class property initialization

              If you export any classes with properties that are other classes (declared by you or by the standard library) like this:

              1class Thing {}23export class Something {4  value: Thing5}

              The compiler will error because you either need to add an initializer for the properties that are classes, or add the ! operator:

              1export class Something {2  constructor(public value: Thing) {}3}45// or67export class Something {8  value: Thing910  constructor(value: Thing) {11    this.value = value12  }13}1415// or1617export class Something {18  value!: Thing19}

              Array initialization

              The Array class still accepts a number to initialize the length of the list, however you should take care because operations like .push will actually increase the size instead of adding to the beginning, for example:

              1let arr = new Array<string>(5) // ["", "", "", "", ""]23arr.push('something') // ["", "", "", "", "", "something"] // size 6 :(

              Depending on the types you’re using, eg nullable ones, and how you’re accessing them, you might encounter a runtime error like this one:

              1ERRO Handler skipped due to execution failure, error: Mapping aborted at ~lib/array.ts, line 110, column 40, with message: Element type must be nullable if array is holey  wasm backtrace:     0: 0x19c4 - <unknown>!~lib/@graphprotocol/graph-ts/index/format         1: 0x1e75 - <unknown>!~lib/@graphprotocol/graph-ts/common/collections/Entity#constructor        2: 0x30b9 - <unknown>!node_modules/@graphprotocol/graph-ts/global/global/id_of_type

              To actually push at the beginning you should either, initialize the Array with size zero, like this:

              1let arr = new Array<string>(0) // []23arr.push('something') // ["something"]

              Or you should mutate it via index:

              1let arr = new Array<string>(5) // ["", "", "", "", ""]23arr[0] = 'something' // ["something", "", "", "", ""]

              GraphQL schema

              This is not a direct AssemblyScript change, but you may have to update your schema.graphql file.

              Now you no longer can define fields in your types that are Non-Nullable Lists. If you have a schema like this:

              1type Something @entity {2  id: Bytes!3}45type MyEntity @entity {6  id: Bytes!7  invalidField: [Something]! # no longer valid8}

              You’ll have to add an ! to the member of the List type, like this:

              1type Something @entity {2  id: Bytes!3}45type MyEntity @entity {6  id: Bytes!7  invalidField: [Something!]! # valid8}

              This changed because of nullability differences between AssemblyScript versions, and it’s related to the src/generated/schema.ts file (default path, you might have changed this).

              Other

              • Aligned Map#set and Set#add with the spec, returning this (v0.9.2⁠)
              • Arrays no longer inherit from ArrayBufferView, but are now distinct (v0.10.0⁠)
              • Classes initialized from object literals can no longer define a constructor (v0.10.0⁠)
              • The result of a ** binary operation is now the common denominator integer if both operands are integers. Previously, the result was a float as if calling Math/f.pow (v0.11.0⁠)
              • Coerce NaN to false when casting to bool (v0.14.9⁠)
              • When shifting a small integer value of type i8/u8 or i16/u16, only the 3 respectively 4 least significant bits of the RHS value affect the result, analogous to the result of an i32.shl only being affected by the 5 least significant bits of the RHS value. Example: someI8 << 8 previously produced the value 0, but now produces someI8 due to masking the RHS as 8 & 7 = 0 (3 bits) (v0.17.0⁠)
              • Bug fix of relational string comparisons when sizes differ (v0.17.8⁠)
              ⁠Edit on GitHub⁠

              CuratingGraphQL Validations Migration Guide
              On this page
              • Features
              • New functionality
              • Optimizations
              • Other
              • How to upgrade?
              • Breaking changes
              • Nullability
              • Variable Shadowing
              • Null Comparisons
              • Casting
              • Nullability check with property access
              • Operator overloading with property access
              • Value initialization
              • Class property initialization
              • Array initialization
              • GraphQL schema
              • Other
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