Problems structuring and querying a table properly - DynamoDB - amazon-dynamodb

Question

I am new to dynamoDB. I am having difficulty developing a table structure. I have data that can best be thought of as a folder structure. There are folders which are nested in parent folders. Most of the time, I will be querying for all folders with a given parent folder, however, there are times when I will be querying individual folders.
If I use the parent_id (parent folder) as the partition key and the id of the individual folder as the sort key, I believe that this creates a table where all related files are stored together and I can query them efficiently. However, I have questions.
First, the query "works" in that it returns the data, but is it written so that it queries the data correctly and is not merely scrolling through the whole table?
router.get("/api/children_folders/:parent_id", (req, res, next) => {
let parent_id = req.params.parent_id;
let params = {
TableName: tableName,
KeyConditionExpression: "parent_id = :pid",
ExpressionAttributeValues: {
":pid": parent_id,
},
ScanIndexForward: false,
};
docClient.query(params, (err, data) => {
if (err) {
console.log(err);
return res.status(err.statusCode).send({
message: err.message,
status: err.statusCode,
});
} else {
return res.status(200).send(data);
}
});
});
Second, if I want to query for individual tags, do I need to pass in a combination of the parent folder ID and the actual ID, or is this OK?
router.get("/api/folder/:folder_id", (req, res, next) => {
let tag_id = req.params.folder_id;
let params = {
TableName: tableName,
KeyConditionExpression: "folder_id = :fid",
ExpressionAttributeValues: {
":fid": folder_id,
},
Limit: 1,
};
docClient.query(params, (err, data) => {
if (err) {
console.log(err);
return res.status(err.statusCode).send({
message: err.message,
status: err.statusCode,
});
} else {
if (!_.isEmpty(data.Items)) {
return res.status(200).send(data.Items[0]);
} else {
return res.status(404).send();
}
}
});
});
I just feel like I am missing some thing here and I want to make sure that I am grabbing the data correctly.

Answer 1

The PK, should be something that would divide the load equally (ideally). I don't the fully picture of your problem but assuming you can chose a good parent folder as a partition key, then you can insert every file/dir with a sort key representing its full path
For example:
PK SK
/home /username/pictures/cat.jpg
This way if you want to get a specific item you can use the get item request
var params = {
Key: {
"PK": { "S": "/home" },
"SK": { "S": "/username/pictures/cat.jpg" }
},
TableName: tableName
};
var result = await dynamodb.getItem(params).promise()
Now if you want to list all the files in "/home/username/pictures" you can use begins with query
const params = {
TableName: 'tablenName',
KeyConditionExpression: '#PK = :root_path and begins_with(#SK, :sub_path)',
ExpressionAttributeNames:{
"#user_id": "root_path",
"#user_relation": 'sub_path'
},
ExpressionAttributeValues: {
":root_path": "/home",
":sub_path": "/username/pictures"
}
}