javascript - 使用 Promise all 并行执行函数

Question

我需要执行几个并行函数

第一个功能： 数据库获取操作，即从数据库中查找库存详细信息

第二个功能： 处理db结果并将结果保存为文件

我正在使用两个promise，背靠背执行上述功能，我觉得这不是正确的方法。有没有更好的方法来处理这些函数调用。我根据以下代码得到结果，但想知道任何其他方式。

这样做的方式如下：

let allQuery = {
  sql: "SELECT * from inventory",
};
let inventoryQuery = {
  sql: "SELECT * from inventory where inventory='1'",

};
let nearbyQuery = {
  sql: "SELECT * from inventory where inventory='2",

};
let firstPromises = [dbService.fetch(allQuery),
  dbService.fetch(inventoryQuery),
  dbService.fetch(nearbyQuery)
];
Promise.all(firstPromises)
    .then((values) => {
      let all = values[0];
      let inventory = values[1];
      let nearby = values[2];
      let fileKey1 = folderName + '/' + all.QueryExecutionId + '.csv';
      let fileName1 = all.QueryExecutionId + '.csv';
      let fileKey2 = folderName + '/' + inventory.QueryExecutionId + '.csv';
      let fileName2 = inventory.QueryExecutionId + '.csv';
      let fileKey3 = folderName + '/' + nearby.QueryExecutionId + '.csv';
      let fileName3 = nearby.QueryExecutionId + '.csv';
      let secondPromises = [s3Service.s3StreamDownload(bucketName, fileKey1, fileName1),
        s3Service.s3StreamDownload(bucketName, fileKey2, fileName2),
        s3Service.s3StreamDownload(bucketName, fileKey3, fileName3)
      ];
      Promise.all(secondPromises)
          .then((values) => {
            console.log('Do later operation');

          }).catch((error) => {
        debug(`Error in promises ${error}`);

      });

    }).catch((error) => {
  debug(`Error in promises ${error}`);

});

标签： javascriptnode.jspromiseparallel-processing

Answer 1

我认为提取内部函数然后将它们链接在一起会更具可读性：

Promise.all(firstPromises)
  .then(transformToSecondPromises)
  .then(Promise.all)
  .then(values => {/* do later operation */})
  .catch(error => { debug(`Error in promises ${error}`) })

function transformToSecondPromises ([all, inventory, nearby]) {
  const fileKey1 = folderName + '/' + all.QueryExecutionId + '.csv';
  const fileName1 = all.QueryExecutionId + '.csv';
  const fileKey2 = folderName + '/' + inventory.QueryExecutionId + '.csv';
  const fileName2 = inventory.QueryExecutionId + '.csv';
  const fileKey3 = folderName + '/' + nearby.QueryExecutionId + '.csv';
  const fileName3 = nearby.QueryExecutionId + '.csv';
  return [
    s3Service.s3StreamDownload(bucketName, fileKey1, fileName1),
    s3Service.s3StreamDownload(bucketName, fileKey2, fileName2),
    s3Service.s3StreamDownload(bucketName, fileKey3, fileName3)
  ];
}