Adding a where clause to AWS DynamoDB - amazon-web-services

Question

I am trying to create a getItem request in AWS Lambda to access DynamoDB like so:
dynamodb.getItem({
TableName: "DataTable",
Key: {
user: {
S: user
},
deleted: {
BOOL: false
}
}
}, function(err, data) {
if (err) return fn(err);
else {
if ('Item' in data) {
fn(null, user);
} else {
fn(null, null); // User not found
}
}
});
It worked fine when I passed the user in as that was the primary key on the table. I added a deleted boolean to create a soft delete on users. But one I added that in the schema errors started to happen as deleted isn't part of the primary key. I want a way to add it as a where clause coming from the relational DB world. How is this done? Thanks. :o)

Answer 1

The getItem cannot be used if the data has to be filtered by any non-key attributes.
I think in the above case, the 'deleted'attribute is a non-key attribute. So, the Query API should be used to filter the data along with key attribute.
Please refer the FilterExpression in the below example.
FilterExpression : 'deleted = :createdate'
(AWS.Request) query(params = {}, callback)
Sample code:-
var params = {
TableName : table,
KeyConditionExpression : 'yearkey = :hkey and title = :rkey',
FilterExpression : 'deleted = :deleted',
ExpressionAttributeValues : {
':hkey' : year_val,
':rkey' : title,
':deleted' : {BOOL : false}
}
};
docClient.query(params, function(err, data) {
if (err) {
console.error("Unable to read item. Error JSON:", JSON.stringify(err,
null, 2));
} else {
console.log("GetItem succeeded:", JSON.stringify(data, null, 2));
}
});
For your use case, the key, filter condition and expression attribute value should be as mentioned below:-
KeyConditionExpression : 'user = :user',
FilterExpression : 'deleted = :deleted',
ExpressionAttributeValues : {
':user' : 'John',
':deleted' : {BOOL : false}
}