Querying single item in DynamoDB using Lambda - node.js

Question

I have a table in DynamoDB that stores some data, the partition key - username - gets stored as the CognitoUser name along with a sort key provided by the user (Sort key is "Code") - these make up the primary key.
I want to query a single Item in DynamoDB that matches the primary key. 
Here is my Lambda function;
exports.handler = (event, context, callback) => {
    const type = event.type;
    if (type === 'all'){
        const params = {
            TableName: 'test-record'
        };
        dynamodb.scan(params,function(err,data){
            if(err){
                console.log(err);
                callback(err);
            }else{
                console.log(data);
                const items = data.Items.map(
                    (dataField) =>{
                       return{
                           Date: dataField.Date.S,
                           Code: dataField.Code.S,
                           TelNumber: +dataField.TelNumber.N,
                           NameOfPerson: dataField.NameOfPerson.S,
                           FileNum: dataField.FileNum.S,
                           Purpose: dataField.Purpose.S,
                       };
                    }
                    );
                callback(null,items);
            }
        });
    }else if(type == 'single'){
        const params = {
            Key: {
                "username": {
                    S: dataField.username.S,
                },
                "Code": {
                    S: dataField.Code.S
                }
            },
            TableName: "test-record"  
        };
        dynamodb.getItem(params, function(err,data){
            if(err){
                console.log(err);
                callback(err);
            }else{
                console.log(data);
                callback(null, data);
            }
        });
    }else{
        callback('Something went wrong');
    } };
If i hardcode "username" and "Code" in this function, it works and returns the correct data, but using the above pasted code gives me an error saying;
{ "errorMessage": "RequestId: c410e493-b774-11e7-a528-37d94b51b57b Process exited before completing request" }
Any ideas how to get items from DynamoDB  without having to hard them into Lambda?

Answer 1

One thing, I don't see how datafield is being initialized in the if(type == 'single') if statement outside of the map function...
But aside from that, I think you should try using Expression Attributes names and values. I haven't tested this with getItem but it works for query:
I made the variable i used to get query the table from the my event body like:
const queryVariable = eval(JSON.stringify(e.body));
Then I used Expression Attributes and Expression Values in my params to make the query.
var params = {
TableName: 'tablename',
KeyConditionExpression: '#hkn = :v and begins_with(#sk, :skv)',
ExpressionAttributeNames: {
"#hkn": "Hash_Key_Name",
"#sk": "SortKeyName"
},
ExpressionAttributeValues: {
":qv": queryValue,
":skv": sortKeyValue
}
}
Then you can make your call to docClient.query(params, function(err, data) so on and so forth. Maybe you can use this instead of getItem.
But if you don't need to grab a single item and want to query your database for some variable keys, try this.
but a very simple Lambda function I've written to get data from DDB into a React Native Application goes like this:
const AWS = require('aws-sdk');
const docClient = new AWS.DynamoDB.DocumentClient({region: 'us-west-2'});
exports.handle = function(e, ctx, cb) {
var params = { TableName: 'TableName' };
docClient.scan(params, function(err, data) {
if(err) {
cb(err, null);
} else {
cb(null, data.Items);
}
});
}
Make sure the role being used to execute the lambda function include Dynamodb read access (at least)