We Keep Coding

How to create an item with an index in DynamoDB?

I have been looking everywhere on AWS docs for any information on this and can find absolutely none. The only answer I keep getting everywhere I look is how to query or scan using a secondary index, on already-indexed data. But how do you add a value to the index-attribute of an item in the first place? I am using AWS SDK for JavaScript so JS-specific info would be most helpful, but any info on this would be so much better than what AWS has provided.
I tried to add an item with params like the following, where I simply used the names of indexes as attributes (date and timestamp):
const params = {
TableName: 'Posts_Table',
Item: {
'username' : user,
'image_id' : uuid(),
'date' : date,
'timestamp' : timestamp
}
}
But what ended up happening is date and timestamp were simply added as normal attributes that aren't able to be queried.

You've got some fundamental misunderstanding going on. You don't give enough code or examples for me to guess what you're really attempting. For example, I don't know what your table's keys are. So here's a primer:
You only write items to the base table (never directly to an index). Items can have a variety of attributes. Each item must have unique key attributes in the base table.
You can create a GSI against the table, including after the table has data. When constructing the GSI you select what its key attributes will be.
When you want to use the GSI you must specify it in the query as your Scan or Query target.
Are you trying to write to the index? You can't.
Are you trying to query the index by pointing at the base table? You can't.
Are you trying to write an item to the base table without specifying its primary keys? You can't.

How to create an item with an index in DynamoDB?
You can not create an item without an index in DynamoDB.
When you create a table, you specify the Primary Key which is your index.
When you add an item, you have to provide the Primary Key.
You can also make use of Global Secondary Indexes which technically create a new table with that index under the hood.
But what ended up happening is date and timestamp were simply added as normal attributes that aren't able to be queried.
If you want to be able to query an attribute, that attribute has to be a Primary Key (Partition or Composite) or a Global Secondary Index.

How to update primary key and it's references to other tables at the same time

I have a main table with primary key as 'main_id'.
This 'main_id' is being used a foreign key in two tables : 'sub_table1', 'sub_table2'
I have a requirement where I need to change the 'main_id' and it's references in 'sub_table1' and 'sub_table2'.
I am on Nodejs and using Bookshelf and Knex.
So far I tried updating the sub_tables first and then tried updating the main_table.
But it threw error 'Foreign_key constraint being violated'.
I'm new at using Bookshelf.
Please help

Foreign keys are absolutely constant and this might not be what you actually want to do. I mean, there is no real reason why you would like to change the id as it's an identification for you as a developer to work with, not something that should be able to be overwritten. If for some reason you need the user to have something similar to an identification that they can overwrite, you can simply create a new column called for example 'code' or 'customId' (or whatever, you got the point) and make it unique.

Relay: fetch for recursive data returns null

I have a recursive data structure to be fetched and displayed. I have a graph ql type as follow:
human {
name,
children: [human]
}
Now I wanted to incrementally fetch data and hence used to react classes HumanList and HumanItem, where I've used relay to fetch children only when a item is clicked. In my actual code relay gives children a null on very click i.e. on rendering very first set of children. I tried test code on relay playground and found similar issue. Here is the link to gist. Playground.js contains the code part and Playground.gql.js contains schema part. Clicking on each number open children under it. After 3 or 4 level it starts showing Found children as null. For me it happens on 1.1.2.2. If it doesn't happens so for you then try adding more levels in SCHEMA code and the bug would pop in.
I've already checked relay issues #246 and #536 but none of them helped.
Any help is very much welcome.

This was a bug. Given a plural field, when the time came to make a query for new data, we would diff what we have in the store with what the application wants. The bug was that we would assume that all records of a plural field have the same shape in the store, and only use the first store record in any plural field against which to diff. This was of course not true in your case, where some records in a plural field might be expanded and some might be collapsed.
This has been fixed as part of https://github.com/facebook/relay/issues/1243 and will be released in the version after Relay 0.9.1.

Parse.com relations count

I want to query object from Parse DB through javascript, that has only 1 of some specific relation object. How can this criteria be achieved?
So I tried something like this, the equalTo() acts as a "contains" and it's not what I'm looking for, my code so far, which doesn't work:
var query = new Parse.Query("Item");
query.equalTo("relatedItems", someItem);
query.lessThan("relatedItems", 2);

It seems Parse do not provide a easy way to do this.
Without any other fields, if you know all the items then you could do the following:
var innerQuery = new Parse.Query('Item');
innerQuery.containedIn('relatedItems', [all items except someItem]);
var query = new Parse.Query('Item');
query.equalTo('relatedItems', someItem);
query.doesNotMatchKeyInQuery('objectId', 'objectId', innerQuery);
...
Otherwise, you might need to get all records and do filtering.
Update
Because of the data type relation, there are no ways to include the relation content into the results, you need to do another query to get the relation content.
The workaround might add a itemCount column and keep it updated whenever the item relation is modified and do:
query.equalTo('relatedItems', someItem);
query.equalTo('itemCount', 1);

There are a couple of ways you could do this.
I'm working on a project now where I have cells composed of users.
I currently have an afterSave trigger that does this:
const count = await cell.relation("members").query().count();
cell.put("memberCount",count);
This works pretty well.
There are other ways that I've considered in theory, but I've not used
them yet.
The right way would be to hack the ability to use select with dot
notation to grab a virtual field called relatedItems.length in the
query, but that would probably only work for me because I use PostGres
... mongo seems to be extremely limited in its ability to do this sort
of thing, which is why I would never make a database out of blobs of
json in the first place.
You could do a similar thing with an afterFind trigger. I'm experimenting with that now. I'm not sure if it will confuse
parse to get an attribute back which does not exist in its schema, but
I'll find out, by the end of today. I have found that if I jam an artificial attribute into the objects in the trigger, they are returned
along with the other data. What I'm not sure about is whether Parse will decide that the object is dirty, or, worse, decide that I'm creating a new attribute and store it to the database ... which could be filtered out with a beforeSave trigger, but not until after the data had all been sent to the cloud.
There is also a place where i had to do several queries from several
tables, and would have ended up with a lot of redundant data. So I wrote a cloud function which did the queries, and then returned a couple of lists of objects, and a few lists of objectId strings which
served as indexes. This worked pretty well for me. And tracking the
last load time and sending it back when I needed up update my data allowed me to limit myself to objects which had changed since my last query.

Identifying filtered rows with DataTables

I have some issues with a project I inherited that is using DataTables and it's filter functionality.
The issue is that in the main function which populates the table, it has the following code:
var rowPos = mainTable.fnAddData(tableData, false)[0];
var rowData = mainTable.fnSettings().aoData[rowPos];
$(rowData.nTr).attr("id", "UID" + id); // Since the id doesn't always match the row
rowData.ID = id;
Now I know that the 3rd line is pretty much useless unless the 'false' argument of the fnAddData is set to 'true'. This is because the HTML elements don't actually exist in the DOM when set to 'false' so there is no way of setting the 'id' attribute.
I can't use 'true' because it will render the table in about 4 seconds when adding several hundred rows to the table. But when I use 'false' it renders the table almost instantaneously (less than a second). So using the 'true' flag in 'fnAddData()' is not even an option.
I see the last line seems to be doing something, but I've tried to find documentation for that on the DataTables web site but can't seem to find anything of value. I'm assuming it allows someone to bind a UID (unique record ID) to the actual row number, which is essential what is wanted.
The code I have also makes use of the 'fnRowCallback', which tries to set the 'id' attribute at this time, such as:
var id = mainTable.fnSettings().aoData[tablePos].ID;
$(row).attr("id", "UID" + id); // Since the id doesn't always match the row
The main problem is that it does not seem to work! If I apply a table filter and purposely filter out all records except the record which should be 'UID' 3, in the 'fnRowCallback', my 'id' variable is set to 0. So the attribute set is always 'UID0' and causes all sorts of bad references.
Is there a way to properly assign my database record ID to table row's? And then refer them later on, such as in the 'fnRowCallback' function? Or is there some other trick someone has managed to figure out?
Thanks in advance for your time and responses!
Update: 2012.11.01 12:33 - I've added an answer below based on various findings so far!

I've been doing a bit of digging and here are my conclusions so far...
Using a JavaScript object inspection that I found on this SO page (by 'goreSplatter') I was able to dump various DataTables objects.
I realized that my 'rowData' object was a tiny container, as expected. And realized that the 'rowData.ID' property did not originally exist in this data structure. I guess the application developer inserted it himself and it makes sense.
From the 'fnRowCallback()' function, I did the same object inspection to try and find the initial 'rowData' that I initialized my 'ID' on. I found it as follows:
var rowData = mainTable.fnSettings().aoData[tablePos];
And when I dump the value of 'rowData.ID' I realized that my 'ID' value was properly set as expected.
The problem occurs when I do my filter! The 'rowData.ID' seems to always be '0' for some reason. It seems like the DataTables takes a copy of the object but does not set any properties it does not know and thus results in '0'.
So it is definitely a bug (at least, in my opinion)! I will contact the DataTables people to see how they would expect users to bind custom application data to their rows and see if they can also set these properties during a filtering process.
I will report any further findings later on.