编辑:我正在使用node v8.0.0
我刚开始学习如何使用node-postgres访问SQL数据库,但是在访问多个数据库以便以可操作的格式收集数据方面遇到了一些困难,特别是在forEach循环中执行多个查询。经过几次尝试,我正在尝试使用async/await,但是我遇到了以下错误:
await client.connect()
^^^^^^
SyntaxError: Unexpected identifier
当我尝试使用连接池或连续调用.query时,我会得到类似以下的结果:
1
[]
could not connect to postgres Error: Connection terminated
这是我的代码的简化版本:
const { Client } = require('pg');
const moment = require('moment');
const _ = require('lodash');
const turf = require('@turf/turf');
const connString = // connection string
var collected = []
const CID = 300
const snaptimes = // array of times
var counter=0;
const client = new Client(connString);
function createArray(i,j) {
// return array of i arrays of length j
}
await client.connect()
snaptimes.forEach(function(snaptime){
var info = {}; // an object of objects
// get information at given snaptime from database 1
const query1 = // parametrized query selecting two columns from database 1
const result1 = await client.query(query1, [CID,snaptime]);
var x = result1.rows;
for (var i = 0; i < x.length; i++) {
// store data from database 1 into info
// each row is an object with two fields
}
// line up subjects on the hole
const query2 = // parametrized query grabbing JSON string from database 2
const result2 = await client.query(query2, [CID,snaptime]);
const raw = result2.rows[0].JSON_col;
const line = createArray(19,0); // an array of 19 empty arrays
for (var i = 0; i < raw.length; i++) {
// parse JSON object and record data into line
}
// begin to collect data
var n = 0;
var g = 0;
// walk down the line
for (var i = 18; i > 0; i--) {
// if no subjects are found at spot i, do nothing, except maybe update g
if ((line[i] === undefined || line[i].length == 0) && g == 0){
g = i;
} else if (line[i] !== undefined && line[i].length != 0) {
// collect data for each subject if subjects are found
line[i].forEach(function(subject){
const query 3 = // parametrized query grabbing data for each subject
const result3 = await client.query(query3,[CID,subject,snaptime]);
x = result3.rows;
const y = moment(x[0].end_time).diff(moment(snaptime),'minutes');
var yhat = 0;
// the summation over info depends on g
if (g===0){
for (var j = i; j <= 18; j++){
yhat = moment.duration(info[j].field1).add(yhat,'m').asMinutes();
}
} else {
for (var j = i; j <= 18; j++){
if (i<j && j<g+1) {
yhat = moment.duration(info[j].field2).add(yhat,'m').asMinutes();
} else {
yhat = moment.duration(info[j].field1).add(yhat,'m').asMinutes();
}
}
}
collected.push([y,yhat,n,i]);
});
}
n+=line[i].length;
g=0;
}
// really rough work-around I once used for printing results after a forEach of queries
counter++;
if (counter===snaptimes.length){
console.log(counter);
console.log(collected);
client.end();
}
});
for (let snaptime of snaptimes) { ... }
而不是snaptimes.forEach(function (snaptime) { ... });
这样你就不会调用其他函数,迭代步骤的同步也更容易。 - rsp