I need to mark the first(earliest) 10 entries in my table as '1'. How to do this?
I read about query.setRange(0,10) option. I just want to confirm whether this setRange option without any sort applied retrieves the earliest 10 entities of a table?
I don't want to save any date and time to measure this.
If you have some other simpler way to do this, please advise.
Thanks,
Karthick.
You should never count on a database (no matter which one) to sort results without explicitly requesting a specific order. Even if datastore returns the earliest entities, it might change in the future and your software will stop working.
Related
I am working on a reminder app with FLutter. Is the first time I am working with Firestore. I have checked on google but I could not find the way to do it.
I want to have the option that the reminder can be set on specific date but or multiple days. Like Monday, Saturday and Sunday.
How should I setup the database? I tried with timestamp, but is not what I want. Should be ARRAY?
Cheers
Usually you should write your answer more precise. It' hard to help you because we don't even know what you want to do with your app and the solutions depends on that.
If you need to filter the entries a lot according to those days (Mo, To, Fri) you could save them in an array to filter easy on them. Also if you want to get them together with the document you save in Firestore I would recommended to use an array. That way you won't need to call on a different collection with the days to get them. The bad side of saving in an array is that you can't just update it. You would need to download the whole array, edit it and save the whole array again. But if you just save up to 7 days of a week that won't be a big deal.
On the other side if there is no need to filter on the days and to get them together with the document you could save them in a separate collection or subcollection of your document. With this approach each day of the week would be a document and you could update each of them very easy and even add additional data very easy. The bad side of this approach is that you would need to call that collection of days separately of your event document and cause more reads on Firestore.
As you can see it all depends how you want your app to work and that is the reason you could not find anything on the web. Those kind of questions are to unprecise to be answered as you expect it to be. There is no silver bullet for such kind of database structures and even the same apps with same purpose could have completely different structures and work as expected.
I hope I could at least guide you to a direction so you can go the next step.
There's any way to list the kinds that are not being used in google's datastore by our app engine app without having to look into our code and/or logic? : )
I'm not talking about indexes, which I can list by issuing an
gcloud datastore indexes list
and then compare with the datastore-indexes.xml or index.yaml.
I tried to check datastore kinds statistics and other metadata but I could not find anything useful to help me on this matter.
Should I give up to find ways of datastore providing me useful stats and code something to keep collecting datastore statistics(like data size), during a huge period to have at least a clue of which kinds are not being used and then, only after this research, take a look into our app code to see if the kind Model was removed?
Example:
select bytes from __Stat_Kind__
Store it somewhere and keep updating for a period. If the Kind bytes size does not change than probably the kind is not being used anymore.
The idea is to do some cleaning in datastore.
I would like to find which kinds are not being used anymore, maybe for a long time or were created manually to be used once... You know, like a table in oracle that no one knows what is used for and then if we look into the statistics of that table we would see that this table was only used once 5 years ago. I'm trying to achieve the same in datastore, I want to know which kinds are not being used anymore or were used a while ago, then ask around and backup/delete it if no owner was found.
It's an interesting question.
I think you would be best-placed to audit your code and instill organizational practice that requires this documentation to be performed in future as a business|technical pre-prod requirement.
IIRC, Datastore doesn't automatically timestamp Entities and keys (rightly) aren't incremental. So there appears no intrinsic mechanism to track changes short of taking a snapshot (expensive) and comparing your in-flight and backup copies for changes (also expensive and inconclusive).
One challenge with identifying a Kind that appears to be non-changing is that it could be referenced (rarely) by another Kind and so, while it does not change, it is required.
Auditing your code and documenting it for posterity should not only provide you with a definitive answer (and identify owners) but it pays off a significant technical debt that has been incurred and avoids this and probably future problems (e.g. GDPR-like) requirements that will arise in the future.
Assuming you are referring to records being created/updated, then I can think of the following options
Via the Cloud Console (Datastore > Dashboard) - This lists all your 'Kinds' and the number of records in each Kind. Theoretically, you can take a screen shot and compare the counts so that you know which one has experienced an increase or not.
Use of Created/LastModified Date columns - I usually add these 2 columns to most of my datastore tables. If you have them, then you can have a stored function that queries them. For example, you run a query to sort all of your Kinds in descending order of creation (or last modified date) and you only pull the first record from each one. This tells you the last time a record was created or modified.
I would write a function as part of my App, put it behind a page which requires admin privilege (only app creator can run it) and then just clicking a link on my App would give me the information.
We are new to DynamoDB and struggling with what seems like it would be a simple task.
It is not actually related to stocks (it's about recording machine results over time) but the stock example is the simplest I can think of that illustrates the goal and problems we're facing.
The two query scenarios are:
All historical values of given stock symbol <= We think we have this figured out
The latest value of all stock symbols <= We do not have a good solution here!
Assume that updates are not synchronized, e.g. the moment of the last update record for TSLA maybe different than for AMZN.
The 3 attributes are just { Symbol, Moment, Value }. We could make the hash_key Symbol, range_key Moment, and believe we could achieve the first query easily/efficiently.
We also assume could get the latest value for a single, specified Symbol following https://stackoverflow.com/a/12008398
The SQL solution for getting the latest value for each Symbol would look a lot like https://stackoverflow.com/a/6841644
But... we can't come up with anything efficient for DynamoDB.
Is it possible to do this without either retrieving everything or making multiple round trips?
The best idea we have so far is to somehow use update triggers or streams to track the latest record per Symbol and essentially keep that cached. That could be in a separate table or the same table with extra info like a column IsLatestForMachineKey (effectively a bool). With every insert, you'd grab the one where IsLatestForMachineKey=1, compare the Moment and if the insertion is newer, set the new one to 1 and the older one to 0.
This is starting to feel complicated enough that I question whether we're taking the right approach at all, or maybe DynamoDB itself is a bad fit for this, even though the use case seems so simple and common.
There is a way that is fairly straightforward, in my opinion.
Rather than using a GSI, just use two tables with (almost) the exact same schema. The hash key of both should be symbol. They should both have moment and value. Pick one of the tables to be stocks-current and the other to be stocks-historical. stocks-current has no range key. stocks-historical uses moment as a range key.
Whenever you write an item, write it to both tables. If you need strong consistency between the two tables, use the TransactWriteItems api.
If your data might arrive out of order, you can add a ConditionExpression to prevent newer data in stocks-current from being overwritten by out of order data.
The read operations are pretty straightforward, but I’ll state them anyway. To get the latest value for everything, scan the stocks-current table. To get historical data for a stock, query the stocks-historical table with no range key condition.
My table is (device, type, value, timestamp), where (device,type,timestamp) makes a unique combination ( a candidate for composite key in non-DynamoDB DBMS).
My queries can range between any of these three attributes, such as
GET (value)s from (device) with (type) having (timestamp) greater than <some-timestamp>
I'm using dynamoosejs/dynamoose. And from most of the searches, I believe I'm supposed to use a combination of the three fields (as a single field ; device-type-timestamp) as id. However the set: function of Schema doesn't let me use the object properties (such as this.device) and due to some reasons, I cannot do it externally.
The closest I got (id:uuidv4:hashKey, device:string:GlobalSecIndex, type:string:LocalSecIndex, timestamp:Date:LocalSecIndex)
and
(id:uuidv4:rangeKey, device:string:hashKey, type:string:LocalSecIndex, timestamp:Date:LocalSecIndex)
and so on..
However, while using a Query, it becomes difficult to fetch results of particular device,type as the id, (hashKey or rangeKey) keeps missing from the scene.
So the question. How would you do it for such kind of table?
And point to be noted, this table is meant to gather content from IoT devices, which is generated every 5 mins by each device on an average.
I'm curious why you are choosing DynamoDB for this task. Advanced queries like this seem to be much better suited for a SQL based database as opposed to a NoSQL database. Due to the advanced nature of SQL queries, this task in my experience is a lot easier in SQL databases. So I would encourage you to think about if DynamoDB is truly the right system for what you are trying to do here.
If you determine it is, you might have to restructure your data a little bit. You could do something like having a property that is device-type and that will be the device and type values combined. Then set that as an index, and query based on that and sort by the timestamp, and filter out the results that are not greater than the value you want.
You are correct that currently, Dynamoose does not pass in the entire object into the set function. This is something that personally I'm open to exploring. I'm a member on the GitHub project, and if you would like to submit a PR adding that feature I would be more than happy to help explore that option with you and get that into the codebase.
The other thing you might want to explore is having a DynamoDB stream, that will set that device-type property whenever it gets added to your DynamoDB table. That would abstract that logic out of DynamoDB and your application. I'm not sure if it's necessary for what you are doing to decouple it to that level, but it might be something you want to explore.
Finally, depending on your setup, you could figure out which item will be more unique, device or type, and setup an index on that property. Then just query based on that, and filter out the results of the other property that you don't want. I'm not sure if that is what you are looking for, it will of course work, but I'm not sure how many items you will have in your table, and there get to be questions about scalability at a certain level. One way to solve some of those scalability questions might be to set the TTL of your items if you know that you the timestamp you are querying for is constant, or predictable ahead of time.
Overall there are a lot of ways to achieve what you are looking to do. Without more detail about how many items, what exactly those properties will be doing, the amount of scalability you require, which of those properties will be most unique, etc. it's hard to give a good solution. I would highly encourage you to think about if NoSQL is truly the best way to go. That query you are looking to do seems a LOT more like a SQL query. Not saying it's impossible in DynamoDB, but it will require some thought about how you want to structure your data model, and such.
Considering opinion of #charlie-fish, I decided to jump into Dynamoose and improvise the code to pass the model to the set function of the attribute. However, I discovered that the model is already being passed to default parameter of the attribute. So I changed my Schema to the following:
id:hashKey;default: function(model){ return model.device + "" + model.type; }
timestamp:rangeKey
For anyone landing here on this answer, please note that the default & set functions can access attribute options & schema instance using this . However both those functions should be regular functions, rather than arrow functions.
Keeping this here as an answer, but I won't accept it as an answer to my question for sometime, as I want to wait for someone else to hit out a better approach.
I also want to make sure that if a value is passed for id field, it shouldn't be set. For this I can use set to ignore the actual incoming value, which I don't know how, as of yet.
I need to manage the acquisition of many record at hour. About 1000000 records. And I need to get every second the last insert value for every primary key. It works quit well with sharding. I was thinking to try the use os capped collection to get only the last record for every primary key. In order to do this, I made two separated insert, there is a way, into mongodb, to make some kind of trigger to propagate the insert into a collection to another collection?
MongoDB does not have any support for triggers or similar behavior.
The only way to do this is to make it happen in your code. So the code that writes the first entry should also write the second.
People have definitely requested triggers. If they are necessary for your solution, please cast a vote on the feature request.
I disagree with "triggers is needed". People, MongoDB was created to be very fast and to provide as basic functionalities as can be. This is a power of this solution.
I think that here the best think is to create triggers inside Your application as a part of Data Access layer.