AWS Step Functionsでは組み込み関数だけで配列のフィルターやスライスができる（AWS CDK v2）

若槻龍太

2022.06.18

この記事は公開されてから1年以上経過しています。情報が古い可能性がありますので、ご注意ください。

こんにちは、CX事業本部 IoT事業部の若槻です。

今回は、AWS Step FunctionsでIntrinsic functions（組み込み関数）だけで配列のフィルターやスライス（部分選択）をする方法が便利だったので共有したいと思います。

やってみた

検証環境の作成をAWS CDK v2（TypeScript）で行います。次のようなCDKスタックを作成します。

import { Construct } from 'constructs';
import { aws_stepfunctions, Stack, StackProps } from 'aws-cdk-lib';

export class ProcessStack extends Stack {
  constructor(scope: Construct, id: string, props: StackProps) {
    super(scope, id, props);

    const firstTask = new aws_stepfunctions.Pass(this, 'firstTask', {
      parameters: {
        jsonPath1: aws_stepfunctions.JsonPath.stringAt('$.store.book[*].author'),
        jsonPath2: aws_stepfunctions.JsonPath.stringAt('$..author'),
        jsonPath3: aws_stepfunctions.JsonPath.stringAt('$.store.*'),
        jsonPath4: aws_stepfunctions.JsonPath.stringAt('$.store..price'),
        jsonPath5: aws_stepfunctions.JsonPath.stringAt('$..book[2]'),
        jsonPath6: aws_stepfunctions.JsonPath.stringAt('$..book[(@.length-1)]'),
        jsonPath7: aws_stepfunctions.JsonPath.stringAt('$..book[-1:]'),
        jsonPath8: aws_stepfunctions.JsonPath.stringAt('$..book[0,1]'),
        jsonPath9: aws_stepfunctions.JsonPath.stringAt('$..book[:2]'),
        jsonPath10: aws_stepfunctions.JsonPath.stringAt('$..book[?(@.isbn)]'),
        jsonPath11: aws_stepfunctions.JsonPath.stringAt('$..book[?(@.price<10)]'),
        jsonPath12: aws_stepfunctions.JsonPath.stringAt('$..*'),
      },
    });

    new aws_stepfunctions.StateMachine(this, 'stateMachine', {
      stateMachineName: 'stateMachine',
      definition: firstTask,
    });
  }
}

上記をCDK Deployしてスタックをデプロイします。これにより次のDefinitionのステートマシンが作成されます。

{
  "StartAt": "firstTask",
  "States": {
    "firstTask": {
      "Type": "Pass",
      "Parameters": {
        "jsonPath1.$": "$.store.book[*].author",
        "jsonPath2.$": "$..author",
        "jsonPath3.$": "$.store.*",
        "jsonPath4.$": "$.store..price",
        "jsonPath5.$": "$..book[2]",
        "jsonPath6.$": "$..book[(@.length-1)]",
        "jsonPath7.$": "$..book[-1:]",
        "jsonPath8.$": "$..book[0,1]",
        "jsonPath9.$": "$..book[:2]",
        "jsonPath10.$": "$..book[?(@.isbn)]",
        "jsonPath11.$": "$..book[?(@.price<10)]",
        "jsonPath12.$": "$..*"
      },
      "End": true
    }
  }
}

次の入力を指定してステートマシンを実行します。

{
  "store": {
    "book": [
      {
        "category": "reference",
        "author": "Nigel Rees",
        "title": "Sayings of the Century",
        "price": 8.95
      },
      {
        "category": "fiction",
        "author": "Evelyn Waugh",
        "title": "Sword of Honour",
        "price": 12.99
      },
      {
        "category": "fiction",
        "author": "Herman Melville",
        "title": "Moby Dick",
        "isbn": "0-553-21311-3",
        "price": 8.99
      },
      {
        "category": "fiction",
        "author": "J. R. R. Tolkien",
        "title": "The Lord of the Rings",
        "isbn": "0-395-19395-8",
        "price": 22.99
      }
    ],
    "bicycle": {
      "color": "red",
      "price": 19.95
    }
  }
}

すると実行が成功しました。firstTaskのOutputでは各JSONPathの適用結果が取得できています。

各JSONPathと適用結果

各JSONPathとその適用結果をそれぞれ見てみます。

JSONPath1

store内のすべてのbookのauthorを取得。

// JSONPath
$.store.book[*].author

// Result
[
  "Nigel Rees",
  "Evelyn Waugh",
  "Herman Melville",
  "J. R. R. Tolkien"
]

JSONPath2

すべてのauthorを取得。

// JSONPath
$..author

// Result
[
  "Nigel Rees",
  "Evelyn Waugh",
  "Herman Melville",
  "J. R. R. Tolkien"
]

JSONPath3

store内のすべてを取得。

// JSONPath
$.store.*

// Result
[
  [
    {
      "category": "reference",
      "author": "Nigel Rees",
      "title": "Sayings of the Century",
      "price": 8.95
    },
    {
      "category": "fiction",
      "author": "Evelyn Waugh",
      "title": "Sword of Honour",
      "price": 12.99
    },
    {
      "category": "fiction",
      "author": "Herman Melville",
      "title": "Moby Dick",
      "isbn": "0-553-21311-3",
      "price": 8.99
    },
    {
      "category": "fiction",
      "author": "J. R. R. Tolkien",
      "title": "The Lord of the Rings",
      "isbn": "0-395-19395-8",
      "price": 22.99
    }
  ],
  {
    "color": "red",
    "price": 19.95
  }
]

JSONPath4

store内のすべてのpriceを取得。

// JSONPath
$.store..price

// Result
[
  8.95,
  12.99,
  8.99,
  22.99,
  19.95
]

JSONPath5

3番目のbookを取得。

// JSONPath
$..book[2]

// Result
[
  {
    "category": "fiction",
    "author": "Herman Melville",
    "title": "Moby Dick",
    "isbn": "0-553-21311-3",
    "price": 8.99
  }
]

JSONPath6

順番が最後のbookを取得。

// JSONPath
$..book[(@.length-1)]

// Result
[
  {
    "category": "fiction",
    "author": "J. R. R. Tolkien",
    "title": "The Lord of the Rings",
    "isbn": "0-395-19395-8",
    "price": 22.99
  }
]

JSONPath7

順番が最後のbookを取得。

// JSONPath
$..book[-1:]

// Result
[
  {
    "category": "fiction",
    "author": "J. R. R. Tolkien",
    "title": "The Lord of the Rings",
    "isbn": "0-395-19395-8",
    "price": 22.99
  }
]

JSONPath8

最初の2つのbookを取得。

// JSONPath
$..book[0,1]

// Result
[
  {
    "category": "reference",
    "author": "Nigel Rees",
    "title": "Sayings of the Century",
    "price": 8.95
  },
  {
    "category": "fiction",
    "author": "Evelyn Waugh",
    "title": "Sword of Honour",
    "price": 12.99
  }
]

JSONPath9

最初の2つのbookを取得。

// JSONPath
$..book[:2]

// Result
[
  {
    "category": "reference",
    "author": "Nigel Rees",
    "title": "Sayings of the Century",
    "price": 8.95
  },
  {
    "category": "fiction",
    "author": "Evelyn Waugh",
    "title": "Sword of Honour",
    "price": 12.99
  }
]

JSONPath10

isbnを持つすべてのbookをフィルター。

// JSONPath
$..book[?(@.isbn)

// Result
[
  {
    "category": "fiction",
    "author": "Herman Melville",
    "title": "Moby Dick",
    "isbn": "0-553-21311-3",
    "price": 8.99
  },
  {
    "category": "fiction",
    "author": "J. R. R. Tolkien",
    "title": "The Lord of the Rings",
    "isbn": "0-395-19395-8",
    "price": 22.99
  }
]

JSONPath11

priceが10より大きいすべてのbookをフィルター。

// JSONPath
$..book[?(@.price<10)]

// Result
[
  {
    "category": "reference",
    "author": "Nigel Rees",
    "title": "Sayings of the Century",
    "price": 8.95
  },
  {
    "category": "fiction",
    "author": "Herman Melville",
    "title": "Moby Dick",
    "isbn": "0-553-21311-3",
    "price": 8.99
  }
]

JSONPath12

すべての要素を取得。

// JSONPath
$..*

// Result
[
  {
    "book": [
      {
        "category": "reference",
        "author": "Nigel Rees",
        "title": "Sayings of the Century",
        "price": 8.95
      },
      {
        "category": "fiction",
        "author": "Evelyn Waugh",
        "title": "Sword of Honour",
        "price": 12.99
      },
      {
        "category": "fiction",
        "author": "Herman Melville",
        "title": "Moby Dick",
        "isbn": "0-553-21311-3",
        "price": 8.99
      },
      {
        "category": "fiction",
        "author": "J. R. R. Tolkien",
        "title": "The Lord of the Rings",
        "isbn": "0-395-19395-8",
        "price": 22.99
      }
    ],
    "bicycle": {
      "color": "red",
      "price": 19.95
    }
  },
  [
    {
      "category": "reference",
      "author": "Nigel Rees",
      "title": "Sayings of the Century",
      "price": 8.95
    },
    {
      "category": "fiction",
      "author": "Evelyn Waugh",
      "title": "Sword of Honour",
      "price": 12.99
    },
    {
      "category": "fiction",
      "author": "Herman Melville",
      "title": "Moby Dick",
      "isbn": "0-553-21311-3",
      "price": 8.99
    },
    {
      "category": "fiction",
      "author": "J. R. R. Tolkien",
      "title": "The Lord of the Rings",
      "isbn": "0-395-19395-8",
      "price": 22.99
    }
  ],
  {
    "color": "red",
    "price": 19.95
  },
  {
    "category": "reference",
    "author": "Nigel Rees",
    "title": "Sayings of the Century",
    "price": 8.95
  },
  {
    "category": "fiction",
    "author": "Evelyn Waugh",
    "title": "Sword of Honour",
    "price": 12.99
  },
  {
    "category": "fiction",
    "author": "Herman Melville",
    "title": "Moby Dick",
    "isbn": "0-553-21311-3",
    "price": 8.99
  },
  {
    "category": "fiction",
    "author": "J. R. R. Tolkien",
    "title": "The Lord of the Rings",
    "isbn": "0-395-19395-8",
    "price": 22.99
  },
  "reference",
  "Nigel Rees",
  "Sayings of the Century",
  8.95,
  "fiction",
  "Evelyn Waugh",
  "Sword of Honour",
  12.99,
  "fiction",
  "Herman Melville",
  "Moby Dick",
  "0-553-21311-3",
  8.99,
  "fiction",
  "J. R. R. Tolkien",
  "The Lord of the Rings",
  "0-395-19395-8",
  22.99,
  "red",
  19.95
]

できそうで出来なかったこと

ドキュメントではlength()なるものものありましたが、試してみるとエラーとなり使えませんでした。

        jsonPath13: aws_stepfunctions.JsonPath.stringAt('$.store.book.length()'),

Step Functionsでは対応していないようです。

おわりに

AWS Step FunctionsでIntrinsic functions（組み込み関数）だけで配列のフィルターやスライス（部分選択）をする方法が便利だという話でした。

JSONPathめちゃくちゃ便利ですね！ここまで出来るとは思いませんでした。

前回の下記エントリに引き続き、Step Functionsでの便利な配列の処理方法を確認することができて良かったです。

AWS Step FunctionsステートマシンでLambdaを使わずに配列の作成や要素追加を行うアイデア（AWS CDK v2） | DevelopersIO

参考

以上