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@tdharmon tdharmon/example-query.js
Last active Jun 5, 2019

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Query JSON with S3 Select in Node.js
// See tth.im/s3json for a full explanation of this code
const AWS = require('aws-sdk');
const S3 = new AWS.S3();
exports.handler = async (_, context) => {
try {
const query = 'SELECT * FROM s3object[*].results[*] r;';
// test query is against data from https://swapi.co/api/planets/?page=2
const bucket = 'test-bucket-for-s3-select-tutorial';
const key = 'planets.json';
const params = {
Bucket: bucket,
Key: key,
ExpressionType: 'SQL',
Expression: query,
InputSerialization: {
JSON: {
Type: 'DOCUMENT',
}
},
OutputSerialization: {
JSON: {
RecordDelimiter: ','
}
}
}
const data = await getDataUsingS3Select(params);
context.succeed(data);
} catch (error) {
context.fail(error);
}
};
const getDataUsingS3Select = async (params) => {
return new Promise((resolve, reject) => {
S3.selectObjectContent(params, (err, data) => {
if (err) { reject(err); }
if (!data) {
reject('Empty data object');
}
// This will be an array of bytes of data, to be converted
// to a buffer
const records = []
// This is a stream of events
data.Payload.on('data', (event) => {
// There are multiple events in the eventStream, but all we
// care about are Records events. If the event is a Records
// event, there is data inside it
if (event.Records) {
records.push(event.Records.Payload);
}
})
.on('error', (err) => {
reject(err);
})
.on('end', () => {
// Convert the array of bytes into a buffer, and then
// convert that to a string
let planetString = Buffer.concat(records).toString('utf8');
// remove any trailing commas
planetString = planetString.replace(/\,$/, '');
// Add into JSON 'array'
planetString = `[${planetString}]`;
try {
const planetData = JSON.parse(planetString);
resolve(planetData);
} catch (e) {
reject(new Error(`Unable to convert S3 data to JSON object. S3 Select Query: ${params.Expression}`));
}
});
});
})
}
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