I am trying to query Dynomo DB table and I want to go through over the resulting items in a function in my AWS Lambda. I am not able to extract result from Dynamo DB query. It is inside the closure, I am able to console log it, but I am not able to assign it for any variable in the scope of outer function.
What should I do to get it outside?
function check(id) {
//build params
let params = {
TableName: 'demo_table',
KeyConditionExpression: #key =: id,
Limit: 5,
ScanIndexForward: false,
ExpressionAttributeNames: {
#key: process.env.PRIMARYKEY
},
ExpressionAttributeValues: {
: id: id
}
};
//query ddb
let result = {};
ddb.query(params, function(err, data) {
if (err) {
console.log("AN ERROR OCCURED\n");
console.log(err);
} else {
//How to copy the data from here to outside??
//I can console log and see the data
result = data;
}
});
console.log(result); //returns {}
}
const check = async (id) => {
//build params
let params = {
TableName: 'demo_table',
KeyConditionExpression: #key =: id,
Limit: 5,
ScanIndexForward: false,
ExpressionAttributeNames: {
#
key: process.env.PRIMARYKEY
},
ExpressionAttributeValues: {
: id: id
}
};
let result = await new Promise((resolve, rejects) => {
ddb.query(params, function (err, data) {
if (err) rejects(err)
resolve(data)
});
})
console.log(result); //returns {}
}
By using promises you can get the data. database read is an asyncronous operation.
Related
I have this request in server.js file.
app.post("/insertRowtoMain", (req, res) => {
const {nodeid, maintenancetype, personnel, process, date} = req.body;
//console.log("description",description)
let insertQuery = `insert into maintenance(nodeid,maintenancetype, personnel, process, date)
values(${nodeid},'${maintenancetype}',${personnel},'${process}', '${date}') returning id`
pool.query(insertQuery, (err, result) => {
if (!err) {
console.log("insertRowtoMain", result.rows);
res.status(200).send(result.rows);
} else {
res.status(404).json(err.message)
console.log("insertRowtoMain error", err.message)
}
})
})
And I am calling this request function in front-end with this code:
const addNewMainTypes = async () => {
try {
await axios.post(`${serverBaseUrl}/insertRowtoMain`, {
nodeid: newMaintenance.nodeid,
maintenancetype: newMaintenance.maintenancetype,
personnel: newMaintenance.personnel,
process: newMaintenance.process,
date: newMaintenance.date,
});
} catch (err) {
throw err;
}
const maintenance = await getMain();
// console.log("main list", maintenanceList);
setMaintenance(maintenance);
const maintenanceList = await getMainTypes();
// console.log("main list", maintenanceList);
setMaintenanceList(maintenanceList);
};
When I insert a new row to this function, I got the returning id in server.js terminal.
How can I use that Id in front-end?
Save the response of the POST request in a variable and access the data property
// Here, "data" will be a variable with the response data
const { data } = await axios.post(`${serverBaseUrl}/insertRowtoMain`, {
nodeid: newMaintenance.nodeid,
maintenancetype: newMaintenance.maintenancetype,
personnel: newMaintenance.personnel,
process: newMaintenance.process,
date: newMaintenance.date,
});
/* Seems like your API is returning an array of objects with "id" property, so, for example... */
// The following should console.log the first element's id of the array
console.log(data[0]?.id);
I have a sqlite3 database request in my main.js, that is triggered by button click in renderer.js.
The request reaches my main.js. However, I cannot manage to await the results from the database. The issue occurs already in main.js, so I'm stuck even before anything is passed back to the renderer.js.
I hope someone can tell me what I am missing.
Here is my code:
renderer.js
$(document).on('click','#mybtn',function(e){
let query = "SELECT id, name FROM table1"
// send (here is the issue)
window.api.send("db-query", query)
// (next step: receive, might be wrong but not yet my problem)
window.api.receive(channel="receive-db-data", (data) => {
console.log(data);
});
});
main.js
ipcMain.on(channel='db-query', async (e, query) => {
console.log('query received: ' + query);
let data = await db_request(query).then(
function(value) {
console.log('value: ' + value);
return value;
},
function(error) {
console.log('error fetching data from db on query:' + query);
}
)
console.log("response ready: " + data); //returns undefined if 'return value' is used (otherwise nothing)
// to send back to renderer.js later
e.sender.send("db-data", data)
})
let db_request = async (query) => {
let data = []
var sqlite3 = require('sqlite3').verbose();
var dbPath = require('path').resolve(__dirname, '../../Fin.db')
var db = new sqlite3.Database(dbPath)
db.serialize(function(){
db.each(query, function(err, row) {
console.log(row)
data.push({"id": row.id, "name": row.name})
});
});
db.close();
console.log('db_request:' + data)
return data
}
And this is how my terminal looks like:
query received: SELECT id, type, name FROM table1
db_request:
value:
response ready: undefined
{ id: 1, name: 'a' }
{ id: 2, name: 'b' }
{ id: 3, name: 'c' }
You have to convert db_request result to a Promise, and the promise will be resolved when all rows are pushed to the data. When you use the await keyword, there is no need to handle a promise with .then chain.
main.js will look like this:
const sqlite3 = require('sqlite3').verbose();
const dbPath = require('path').resolve(__dirname, '../../Fin.db')
ipcMain.on(channel='db-query', async (e, query) => {
console.log('query received: ' + query)
try {
const data = await db_request(query); // remove .then
console.log('value: ' + data)
// to send back to renderer.js later
e.sender.send("db-data", data)
} catch (error) {
console.log('error fetching data from db on query:' + query);
e.sender.send("db-data", []) // send empty data or error ???
}
})
let db_request = (query) => {
const db = new sqlite3.Database(dbPath)
return new Promise((resolve, reject) => { // return a promise
// I think you dont need serialize for this case
const data = []
db.each(query, (err, row) => {
console.log(err, row)
if (!err) {
data.push({"id": row.id, "name": row.name})
}
}, (error) => {
if (error) {
reject(error)
} else {
resolve(data)
}
});
})
}
Below is the piece of code i have written , to get the result but null in response
I am using selectObjectContent api to get the results with the simple SQL query
const bucket = 'myBucketname'
const key = 'file.json.gz'
const query = "SELECT * FROM s3object "
const params = {
Bucket: bucket,
Key: key,
ExpressionType: "SQL",
Expression: query,
InputSerialization: {
CompressionType: "GZIP",
JSON: {
Type: "LINES"
},
},
OutputSerialization: {
JSON: {
RecordDelimiter: ","
}
}
}
s3.selectObjectContent(params,(err, data) => {
if (err) {
console.log(data)
} else {
console.log(err)
}
})
I have found the solution to it. was logging error when getting successfull result/data , so corrected it below. Also i have found the way to read stream buffer data
s3.selectObjectContent(params,(err, data) => {
if (err) {
console.log(err)
} else {
console.log(data)
}
})
const eventStream = data.Payload;
// Read events as they are available
eventStream.on('data', (event) => {
if (event.Records) {
// event.Records.Payload is a buffer containing
// a single record, partial records, or multiple records
var records = event.Records.Payload.toString();
console.log( records )
} else if (event.Stats) {
console.log(`Processed ${event.Stats.Details.BytesProcessed} bytes`);
} else if (event.End) {
console.log('SelectObjectContent completed');
}
I am currently using the JavaScript AWS SDK for DynamoDB and I am trying to parse the data I get from a DynamoDB call, but it always returns undefined. It does print the result successfully, but trying to store that data in a variable is unsuccessful. Below is how I am attempting to do it.
const AWS = require("aws-sdk");
AWS.config.update({ region: "us-east-1" });
const dynamoDb = new AWS.DynamoDB({ apiVersion: "2012-08-10" });
const promisify = foo =>
new Promise((resolve, reject) => {
foo((error, result) => {
if (error) {
reject(error);
} else {
resolve(result);
}
});
});
const params2 = {
TableName: "Users",
Key: {
userID: { S: "123456789" },
},
};
const test = params => {
dynamoDb.getItem(params, function(err, data) {
if (err) {
console.log("Error", err);
} else {
console.log("Success", data.Item);
return data.Item;
}
});
};
let user = test(params2);
console.log("User:", user);
I believe it has to do with getItem being asynchronous and I have researched how to implement a promise into this code, but I cannot get the correct syntax. Any and all help is greatly appreciated. Thank you.
The problem you have is that you are not returning anything from your test function. So it is expected that you get undefined outside.
Try to do it like this:
// used aws promise api https://docs.aws.amazon.com/sdk-for-javascript/v2/developer-guide/using-promises.html
function test(params) {
return dynamoDb.getItem(params).promise();
}
test(params2).then(
user => {
console.log('User:', user);
},
error => {
console.log('Error:', error);
},
);
Some further read:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function
My problem is, I want to make INSERT query for every object from JSON using some loop, but I almost always got an error "Cannot set headers after they are sent to the client".Can someone help?Tnx
const connection = require('./config');
module.exports.excel = function (req, res) {
var _query = 'INSERT INTO excel (id, first_name, last_name) values ?';
var jsonData = req.body;
var values = [];
function database() {
return new Promise((resolve, reject) => {
jsonData.forEach((value) => {
values.push([value.id, value.first_name, value.last_name]);
connection.query(_query, [values], (error, results) => {
if (error) {
reject(
res.json({
status: false,
message: error.message
}))
} else {
resolve(
res.json({
status: true,
data: results,
message: 'Excel file successfully created in database'
}))
}
});
});
})
}
async function write() {
await database();
}
write();
}
After I got JSON from my Angular 6 front I put req.body into jsonData and try with forEach to put every object("value" in this case) into query and write that into Excel file.
You will have to wrap each query in a Promise and wait for all to complete before sending the response using Promise.all
Not that database() is going to throw when one of the queries fail and you won't have any access to the resolved promises.
const connection = require('./config');
module.exports.excel = function(req, res) {
const _query = 'INSERT INTO excel (id, first_name, last_name) values ?';
const jsonData = req.body;
function database() {
return Promise.all(
jsonData.map(
value =>
new Promise((resolve, reject) => {
const values = [value.id, value.first_name, value.last_name]
connection.query(_query, [values], (error, results) => {
if (error) {
reject(error.message);
return;
}
resolve(results);
});
})
)
);
}
async function write() {
try {
const results = await database();
res.json({
status: true,
data: results,
message: 'Excel file successfully created in database'
});
} catch (e) {
res.json({
status: false,
message: e.message
});
}
}
write();
};