AWS Lambda and Dynamo db: How to filter the result of scan by multiple parameters? - amazon-web-services

Question

I am new to AWS and dynamo. I working on my project with React.js front-end and AWS (Gateway API, Lambda, Dynamo) backend.
This is my app location:
https://www.alphaux.com
After I click "Get Hint", I receive server response. If I click on a keywords - these keywords will be added to the list of GET params for the request like:
topic=blah&keywords=blah1,blah2,blah3
Here are the details of my problem:
In my Lambda:
..
const docClient = new AWS.DynamoDB.DocumentClient({region: 'us-west-2'});
exports.handler = async (event) => { ..
from GET I am receiving the following params:
const topicName = event.queryParams.topic="React";
const keywords = event.queryParams.topic.keywords="blah1,blah2,blah3";
..some code here converts keywords string into array:
const keywordsArray = [blah1,blah2,blah3];
In dynamodb they exist in the following way:
[ { "S" : "javascript" }, { "S" : "programming" }, { "S" : "React" } ]
My Primary partition key is: id (Number)
I have tried different ways and approaches, used scan and query - nothing works. I am stuck..
I have tried the following approach:
const listToObjectMappings = () => {
let x = {};
/* keywords hardcoded for now: */
const keywords = ["javascript", "React"];
keywords.map(item => x[':' + item] = item)
return x
}
let mappings = listToObjectMappings()
let joined = Object.keys(mappings).join();
var params2 = {
TableName : "my-little-table",
FilterExpression: 'topic = :topic and #keywords IN (' + joined + ')',
ExpressionAttributeNames: {
'#keywords' : 'keywords'
},
ExpressionAttributeValues:{
":topic" : "React"
}
};
var params = {
TableName: "my-little-table",
FilterExpression: "#topic = :topic",
ExpressionAttributeNames: {
"#topic": "topic"
},
ExpressionAttributeValues: {
":topic": "React"
}
};
let result;
try {
/* scan DB */
result = await docClient.scan(params).promise();
}
catch(ex) {
result = ex;
}
When I use "scan", the result is always empty [] if I am trying to use "keywords".
It works only with bare minimum like:
const params = {
TableName : currentTable,
FilterExpression:'topic = :topic',
ExpressionAttributeValues:{
":topic" : requestedTopic
}
};
..which gives me all records based on requestedTopic.
If I am using "query" it complains that my key name ("id") is too short and has to be at least 3 chars long.
I am stuck and gracefully asking for your help!
Thank you!

Answer 1

If you're trying to match the topic and any one of the keywords then use something like this:
const params = {
TableName: 'mytable',
FilterExpression: '#tp = :tp AND (contains(#kw, :kw1) OR contains(#kw, :kw2))',
ExpressionAttributeNames: {
'#tp': 'topic',
'#kw': 'keywords',
},
ExpressionAttributeValues: {
':tp': 'React',
':kw1': 'react',
':kw2': 'react-router',
},
};
If you're trying to match the topic and all of the keywords then use something like this:
const params = {
TableName: 'mytable',
FilterExpression: '#tp = :tp AND contains(#kw, :kw1) AND contains(#kw, :kw2)',
ExpressionAttributeNames: {
'#tp': 'topic',
'#kw': 'keywords',
},
ExpressionAttributeValues: {
':tp': 'React',
':kw1': 'react',
':kw2': 'react-router',
},
};