I'm working on a side project right now for an email client. I'm using a library to handle the retrieval of the messages from the server. However, I have a question on caching.
I don't want to fetch the entire list of headers everytime I load the client. Ideally, what I'd like to do is cache them and then update the list with what is on the server.
What's the best way to go about this? Should I store all the header information (including the server's message ID #) in a database, load the headers from that DB. Then as a background task sync up with the server...
Or is there a better way?
Look at the webmail sample of this open source project that use local caching:
http://mailsystem.codeplex.com/
If I remember well, he used a combination of local RFC822 plain text email storing with the message id as the filename and an index file with high level data.
Maybe the message itself where zipped to save disc space.
That's just a sample for the library, so don't expect code art there, but that's a start.
Related
I'm a little new to GraphQL and this question falls under "It cannot possibly be this hard. I have to be missing something."
I have a fairly standard GraphQL/Apollo/React application split into client and server. Everything is working well with the client making API calls and getting data back from the server. The client is even able to upload files to the server. However, I now need the server to stream back files saved on disk. That's it.
This is the "I have to be missing something" part. Everything I've seen in the docs and on Stackoverflow is some variation of pushing the file back from the server and through the GraphQL query as a base64-endocded string and then doing some very hacky stuff on the client, often involving a hidden href tag and a simulated click. To this I say, "What???"
Seriously. There are files on disk that the server knows how to find. The client needs to show a button to the user that they can click on to download the file. That's it. Every other framework in every other language has an easy way to do this. Can someone show me the incredibly simple thing that I'm missing here?
Thanks,
Alex
What you're missing is that GraphQL really shouldn't be used for this purpose.
While GraphQL itself does not specify a specific format for serializing responses, the de facto format is JSON. And the only way to get the file inside a JSON response is if it's serialized as a string.
If you want to serve static content, you should set up Nginx, Apache or another web server that's been built with that in mind. Alternatively, if you're already using some existing web server library like Express, it most likely has tools for serving static content as well.
Just because you have a GraphQL endpoint does not necessarily mean it should be the only way your client communicates with your backend.
I'm trying to scheme how I'm going to accomplish this and so far I have the following:
I grab a file in the front end and on submit send the file name and type to the back end where it generates a presigned URL. I send that to the FE. I then send the file on the front end.
The issue here is that when I generate the presign, I want to commit my UUID filename going to S3 in my database via the back end. I don't know if the front end will successfully complete this task. I can think of some janky ways to garbage collect this - but I'm wondering, is there a typically prescribed way to do this that doesn't introduce the possibility of failures the BE isn't aware of?
Yes there's an alternate way. You can configure your bucket so that it sends an event whenever an object is created/updated. You can either send this event to a SNS topic or AWS Lambda.
From there you can make a request to your Phoenix app webhook, that can insert it into the database.
The advantage is that the event will come only when the file has been created.
For more info, you can read the following: https://docs.aws.amazon.com/AmazonS3/latest/dev/NotificationHowTo.html
The way I'm currently handling this is as such:
Compress the image client side.
Send the image to the backend application server.
Create a UUID on the backend.
Send the image from s3 to the backend, using the UUID as the key.
On success, put the UUID into the database.
Respond to the client with the UUID so it can display the image.
By following these steps, you don't introduce error into your database.
Please presume that I do not know anything about any of the things I will be mentioning because I really do not.
Most OpenData sites have the possibility of exporting the presented file either in for example .csv or .json formats (Example). They also always have an API tab (Example API).
I presume using the API would mean that if the data is updated you would receive the change whereas exporting it as .csv would mean the content will not be changed anymore.
My questions is: how does one use this API code to display the same table one would get when exporting a .csv file.
Would you use a database to extract this information? What kind of database and how do you link the API to the database?
I presume using the API would mean that if the data is updated you
would receive the change whereas exporting it as .csv would mean the
content will not be changed anymore.
You are correct in the sense that, if you download the csv to your computer, that csv file won't be updated any more.
An API is something you would call - in this case, you can call the API, saying "Hey, do you have the latest data on xxx?", and you will be given back the latest information about what you have asked. This does not mean though, that this site will notify you when there's a new update - you will have to keep calling the API (every hour, every day etc) to see if there are any changes.
My questions is: how does one use this API code to display the same
table one would get when exporting a .csv file.
You would:
Call the API from a server code, or a cloud service
Let the server code or cloud service decipher (or "Parse") the response
Use the deciphered response to create a table made out of HTML, or to place it into a database
Would you use a database to extract this information? What kind of
database and how do you link the API to the database?
You wouldn't necessarily need a database to extract information, although a database would be nice to place the final data inside.
You would first need some sort of way to "call the REST API". There are many ways to do this - using Shell Script, using Python, using Excel VBA etc.
I understand this is hard to visualize, so here is an example of step 1, where you can retrieve information.
Try placing in the below URL (taken from the site you showed us) in your address bar of your Chrome browser, and hit enter
http://opendata.brussels.be/api/records/1.0/search/?dataset=associations-clubs-sportifs
See how it gives back a lot of text with many brackets and commas? You've basically asked the site to give you some data, and this is the response they gave back (different browsers work differently - IE asks you to download the response as a .json file). You've basically called an API.
To see this data more cleanly, open your developer tools of your Chrome browser, and enter the following JavaScript code
var url = 'http://opendata.brussels.be/api/records/1.0/search/?dataset=associations-clubs-sportifs';
var xhr = new XMLHttpRequest();
xhr.open('GET', url);
xhr.setRequestHeader('X-Requested-With', 'XMLHttpRequest');
xhr.onload = function() {
if (xhr.status === 200) {
// success
console.log(JSON.parse(xhr.responseText));
} else {
// error
console.log(JSON.parse(xhr.responseText));
}
};
xhr.send();
When you hit enter, a response will come back, stating "Object". If you click through the arrows, you can see this is a cleaner version of the data we just saw - more human readable.
In this case, I used JavaScript to retrieve the data, but you can use whatever code you want. You could proceed to use JavaScript to decipher the data, manipulate it, and push it into a database.
kintone is an online cloud database where you can customize it to run JavaScript codes, and have it store the data in their database, so you'll have the data stored online like in the below image. This is just one example of a database you can use.
There are other cloud services which allow you to connect API end points of different services with each other, like IFTTT and Zapier, but I'm not sure if they connect with open data.
The page you linked to shows that the API returns values as a JSON object. To access the data you can just send an appropriate http request and the response will be the requested data as a JSON. You can send requests like that over your browser if you want to.
Most languages allow JSON objects to be manipulated pro grammatically if you need to do work on the data.
Restful APIs publish model is "request and publish". Wen you request data via an API endpoint, you would receive response strings in JSON objects, CSV tables or XML.
The publisher, in this case Opendata.brussel.be would update their database on regular basis and publish the results via an API endpoint.
If you want to download the table as a relational data table in a CSV file, you'd need to parse the JSON objects into relational tables. This can be tricky since each JSON response string can vary in their paths.
There're several ways to do it. You can either write scripts to flatten the JSON objects or use a tool to parse and flatten the objects for you.
I use a tool called Acho to turn API endpoints into CSV files. It would parse almost all API endpoints through the parameters and even configure for multiple requests, such as iterative and recursive requests.
Acho API parser
What design is used to store file objects that gets loaded from a website. For instance if I have a website that accepts documents or images. So
Use Case 1.
Users logs in and selects a MS word file on his machine and uploads to the website.
Use Case 2.
User logs in and selects a image on his machine and uploads to the website.
How do I store these file objects in the database
The first step is just getting the file from the AngularJS application to the server. This page talks about sending request to the server from the client and should get you started.
Once you have done that, (assuming you are using PHP) you will need to save the resulting file to the database. This post will get you started with saving files to PostgreSQL, but the details will end up being very specific to your situation:
If you have more questions after reading through those resources please add specific details about your setup to your question.
I am building a website (probably in Wordpress) which takes data from a number of different sources for display on various pages.
The sources:
A Twitter feed
A Flickr feed
A database on a remote server
A local database
From each source I will mainly retrieve
A short string, e.g. for Twitter, the Tweet, and from the local database the title of a blog page.
An associated image, if one exists
A link identifying the content at its source
My question is:
What is the best way to a) store the data and b) retrieve the data
My thinking is:
i) Write a script that is run every 2 or so minutes on a cron job
ii) the script retrieves data from all sources and stores it in the local database
iii) application code can then retrieve all data from the one source, the local database
This should make application code easier to manage - we only ever draw data from one source in application code - and that's the main appeal. But is it overkill for a relatively small site?
I would recommend putting the twitter feed and flickr feed in JavaScript. Both flickr and twitter have REST APIs. By putting it on the client you free up resources on your server, create less complexity, your users won't be waiting around for your server to fetch the data, and you can let twitter and flickr cache the data for you.
This assumes you know JavaScript. Once you get past JavaScript quirks, it's not a bad language. Give Jquery a try. JQuery Twitter plugin Flickery JQuery plugin. There are others, that's just the first results from Google.
As for your data on the local server and remote server, that will depend more on the data that is being fetched. I would go with whatever you can develop the fastest and gives acceptable results. If that means making a REST call from server to sever, then go for it. IF the remote server is slow to respond, I would go the AJAX REST API method.
And for the local database, you are going to have to write server side code for that, so I would do that inside the Wordpress "framework".
Hope that helps.