I have a use case where I am using multiple flutter engines (my flutter app is embeded in Android), each engine has it's own app instance.
I am sharing common data across engines with Hive.
But one problem is, I want to achieve concurrency as multiple writes (which are async, so in case many engines try to write once) can lead to issues.
I tried exploring 'synchronized' package but it doesn't support mutex for multiple isolates.
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The problem I'm dealing with is performance issues when needing to perform multiple Firestore queries in order to reach a result similar to to joins in SQL.
In my Flutter app, which uses Firebase and Firestore, I use Cloud Functions for serving my REST API. My API is the only thing that actually interacts with the Firestore database, not the Flutter app itself. I was always taught to design apps like this (not allowing the client to interact directly with the database) and so continued with that approach.
A potential solution I've seen are the official Firestore plugins for Flutter and have seen people designing their clients to interact directly with Firebase, however I haven't found any official documentation explicitly saying this design is preferred or even ok, and since it goes against when have been taught I haven't tried it yet. Can anyone confirm this or point me to documentation confirming this?
Edit
Perhaps it's worth noting that the reasons I've been told not to have the client connect directly to the database are 1. Security and 2. It would require business logic for managing data to be in the client and that should be handled server-side.
I am a student and very new in flutter app development and still trying to learn flutter. If I have more than one flutter application (As Backend in php, mysqli) and I want to merge in a single application so what I need to do, I researched so much on google but I didn't get any better solution, I want know:
is it possible?
is it very difficult?
what is the requirement?
It depends. You can do it as long as the resources don't conflict.
Everything is a widget in Flutter. An app itself is also a widget. You can take your whole app and put it inside of another widget. The problem is dependencies. Widgets are just lightweight representations of render objects, they declare how the UI looks (size, layout, hittest etc.). The data that populates them comes from business logic. So the answer depends on the business logic of the apps. It is possible if they don't conflict.
For example if there are two apps that creates a TCP socket with the same port, they will conflict. Another example can be Firebase. An app can not be integrated with multiple Firebase projects.
A working example could be multiple RESTful apps. Two apps that makes HTTP request to get data from the backend will not conflict. They will make seperate requests and have seperate states. It is just like having two pages that fetches different data from the backend.
I‘m rather new to distributed databases, though I have already studied related literature (e.g. CAP theorem, CRDT) and implemented some POC to allow scaling my application horizontally.
Now I however face a challenging problem. In ordere to scale the app horizontally, communication between services is done via a distributed queue. As a background here, I do require a custom CRDT method to keep the data eventually consistent, and I do require my application to work like a cache (remotely related to REDIS).
The challenge is now that I also need to persist the data. That requires me to keep the data within the application cache and database eventually consistent. I‘ve checked Cassandra, I saw a ticket [1] where somebody tried to add functionality for custom CRDT merge functionality (which as I mentioned do require for a reason). That never made it into Cassandra, and seems to have a few issues to resolve.
What are my options, either in form of a concrete distributed database engine allowing custom merging, or an algorithm that could help solve the problem (e.g. in form of a db trigger or something like this).
[1] https://issues.apache.org/jira/browse/CASSANDRA-6412
As far as I know, there are very few databases that allow you to specify your own custom conflict resolution algorithms. Tbh. the only one I really found - disclaimer: I'm not a Microsoft Advocate - is Azure CosmosDB. It has MongoDB-compatible API and can be configured to use master-master replication strategy, where you need to specify your own conflict resolution algorithm (using JavaScript). You can use it to define your own merge operation.
If you'll take a look outside of database-native solutions into application-level ones, there are several tools, like ie. Akka (available in both JVM or .NET version) which enables you to write custom CRDTs inside of distributed-data module. JVM version additionally supports multi-datacenter persistence, which is conceptually closer to how commutative CRDTs work and can be integrated with Cassandra backend.
I've implemented a MerkleClock CRDT at my merkle-crdt repository.
You could use an approach that when you update the database record column, you fetch the column's value and then you merge it with your CRDT of your current state and then when you save, you serialise the CRDT as JSON and store it in the database.
Sometimes I need to run maintenance queries, like backfilling data of a new field I just created. How do I do this easily?
Firebase Functions seems targeted towards triggering on certain keywords or on certain schedules.
Basically, whatever I would do in MongoDB's terminal at will, I'd like to do in Firestore easily (even if I have to deploy code).
There is no set of "best practices" per se, but you can easily write programs to access Firebase and Google Cloud resources from your desktop. Just do some web searches for the server SDKs that provide access (there are many for different languages), and initialize them with a service account that has access to write data in the project.
So, I am trying to create a project where I am supposed to Call Web API and store the data in my local storage. Which should still have even if the app is killed and then re-opened.
FYI, data will be large and I will require a significant amount of space in the mobile device.
i will be using firebase for login, the payment transaction and etc.
this is my first answer, I hope to help you.
BloC & Moor are not synonyms, BloC is a reactive state management solution that allows you to better manage the interaction between logic and widgets in a reactive way. Moor is a layer between sqlite and your application, it allows you to deal with sqlite using dart code by reacting to database changes through Streams and Futures
I think you do not need to choose one of the two, if your application is going to handle large amounts of data and will grow exponentially I recommend that you implement both as they complement each other, by designing a SOLID structure.