異步/等待事件流 mapSync 不起作用

Question

我用//******This await does not work */注釋的await命令似乎不起作用。 不確定這是否與它們在事件流中的事實或導入模塊中的承諾問題有關。

當我從映射數組中調用run函數以插入來自多個源的數據時， run函數會立即返回，而不是等到knex完成插入數據。

 app.get("/api/pull/all_data", (req, res)=>{
    const dataSources = [
      {resource: 'DI_ORDER_TYPE', tableName: 'ln_order_type'},
      {resource: 'DI_DATES', tableName: 'ln_dates'},
      {resource: 'WHINR140_INVENTORY', tableName: 'ln_inventory'}
    ]

    dataSources.map(async (ds)=>{
      console.log(`Importing ${ds.resource} into table ${ds.tableName}`)
      await get_all_data(ds.tableName, ds.resource)
    })

    console.log("Import complete")
  })

這是我從上面的代碼調用的run函數。

const request = require('request')
const JSONStream = require('JSONStream')
const es = require('event-stream')
const knex_ln = require('../knex_ln')
const insertData = require('../insert_data')
const create_table = require('../create_table_from_json.js')
const clean_fieldnames = require('../clean_fieldnames')

function run(tableName, resourceName) {
    return new Promise(async (resolve, reject)=>{
        let tableData = []
        let recordCount = 0
        let maxRecords = 10000
        let totalRecords = 0
        // let tableName = 'LN_di_order_type'
        // let resourceName = 'DI_ORDER_TYPE'
        let rowData = {}
        //Delete Existing Data and wait for it to complete
        await knex_ln.schema.hasTable(tableName).then(async (exists)=>{
            if(exists){
                try {
                    await knex_ln(tableName).delete().then(()=>{})
                } catch (error) {
                    
                }
            }
        })
        //Get LN replica data and pipe data into JSONStream
        request(`${process.env.API_BASE_URL}/${process.env.SECURITY_NAME}/${resourceName}`,
        {
            auth: {
                'user': process.env.API_USER,
                'pass': process.env.API_PASS
            }
        }
        )
        .pipe(JSONStream.parse([true, {recurse: true}, `${process.env.SECURITY_NAME}.row`, true]))
        .pipe(es.mapSync(async (row)=>{
            rowData = row
            let cleanData = await clean_fieldnames(row)
            tableData.push(cleanData)
            recordCount += 1
            totalRecords += 1
            if(recordCount >= maxRecords){
                try {
                    //******This await does not work */
                    await create_table(tableName, row)
                } catch (error) {
                    console.log("Unable to create table", error)
                }
               
                //Insert records
                try {
                    //******This await does not work */
                    await insertData(tableName, tableData)
                    console.log(`inserting ${recordCount} records into table ${tableName}`)
                } catch (error) {
                    console.log("Unable to insert data: ", error)
                }
               
                //Reset tracker variables
                recordCount = 0
                tableData = []
            }
        }))
        .on('end', async ()=>{
            await create_table(tableName, rowData)
            await insertData(tableName, tableData)
            console.log(`Inserted ${totalRecords} into table ${tableName}`)
            resolve('OK')
        })
        .on('error',(err)=>{
            reject(err)
        })
    })
}
module.exports = run

這是我的模塊文件，它返回一個承諾

//insert_data.js
const knex_ln = require('./knex_ln')

module.exports = async (tableName, tableData) => 
    new Promise(async (resolve, reject) => {
      try {
        await knex_ln(tableName).insert(tableData)
        console.log("Inserting Data: ", tableData.length)
        resolve()
      } catch (error) {
        console.log("Error inserting data: ", err)
        reject(err)
      }
    })

這是輸出的示例

Importing DI_ORDER_TYPE into table ln_order_type
Importing DI_DATES into table ln_dates
Importing WHINR140_INVENTORY into table ln_inventory
Importing WHWMD210_WAREHOUSE_ITEM_DATA into table ln_warehouse_item_data
Importing TDIPU010_ITEM_BUY_FROM_BP_INFORMATION into table ln_item_buy_from_bp_information
Importing TDIPU001_ITEM_PURCHASE_DATA into table ln_item_purchase_data
Importing TDPCG031_PRICE_BOOKS into table ln_price_books
Importing TDPUR300_PURCHASE_CONTRACTS into table ln_purchase_contracts
Importing TDPUR301_PURCHASE_CONTRACT_LINES into table ln_purchase_contract_lines
Inserted 72 records into table ln_order_type
Inserted 217 records into table ln_purchase_contracts
inserting 10000 records into table ln_inventory
Inserted 4694 records into table ln_purchase_contract_lines
inserting 10000 records into table ln_item_buy_from_bp_information
inserting 10000 records into table ln_dates
inserting 10000 records into table ln_inventory
inserting 10000 records into table ln_price_books
inserting 10000 records into table ln_item_purchase_data
inserting 10000 records into table ln_inventory
inserting 10000 records into table ln_price_books
inserting 10000 records into table ln_dates
inserting 10000 records into table ln_inventory
inserting 10000 records into table ln_price_books
inserting 10000 records into table ln_item_purchase_data

Answer 1

我實現了自己的 Writable 實現。 我可以在回調函數的幫助下按順序控制調用。只有從上一次迭代收到回調時，才會處理下一次迭代。 我無法使用事件流映射回調來實現這一點

參考https://nodejs.org/api/stream.html#stream_simplified_construction

      readStream.pipe(eventStream.split())
            .pipe(
                 new Writable({
                    write : async (record, encoding,callback)=>{
                               await saveToDatabase(record);
                               callback();
                        }
                })
            )

Answer 2

您只在等待map的內部函數，而不是頂級函數。

您需要在頂級函數中添加一個 await：

await Promise.all(dataSources.map(async (ds)=> {
  console.log(`Importing ${ds.resource} into table ${ds.tableName}`)
  await get_all_data(ds.tableName, ds.resource)
}));

否則，您只是在內部函數中等待，而不是在路由處理程序本身中等待。

Answer 3

我的解決方案是使用 bluebird Promise.each

這將處理數組 dataSources 中的每個項目，並在處理列表中的下一個項目之前等待 promise 返回。

Promise.each(dataSources, function(ds){
     ....
    }).then(()=>{
     ....
    })

http://bluebirdjs.com/docs/api/promise.each.html