Sometime in my life, I want to share something stupid anonymously, somewhere to store data anonymously. Imgur is good, but I am not that bad to abuse the Imgur, last year, they close the api to share image anonymously and I dont want to do some shit crawling stuffs or playing around with their website.I write my own image data storage. The project written in elixir with phoenix web framework supporting and foundation. You can access the projet at http://image.hexalink.xyz
This small web application which helps you to share your images easily and quickly. Those uploading images might be stored on the system until my server storage getting full. If the server’s full, images will be removed to save space.
It’s general and popular to find min/max value of a column in tables with aggregate functions such as min and max.
However, I would like to use vanila way to solve this problem, in addition to explain how does it work with join.
The explaination can help you get a abstract of join and how does it work in processing.
Issue
To help you understand how join can help you approach min and max, we need a good example. Now let start. We got
alot of people in a company, each of them has more then one assessment during their work time. The question is how to
get the latest, newest assessment and the first, oldest assessment. The big question is how to get the latest
and the first assessment answers filter by that person and assessment, remember that an assessment can be done many times. Our table will look like:
table named: assessment_answers;
|-------------+-----------+---------------+--------------------+-------------|
| id | person_id | assessment_id | assessment_answers | inserted_at |
|-------------+-----------+---------------+--------------------+-------------|
| integer, fk | int | int | jsonb | datetime |
|-------------+-----------+---------------+--------------------+-------------|
Thinking approach
To find min/max value of inserted_at value filtered by the person_id and assessment_id, first we need to find all record filtered by person_id and assessment_id, then we must find a min/value of inserted_at via a loop to comparing one to others inserted_at siblings, one which is smaller than others is the smallest and one which is greater than all others is the greatest. This also can be understand in this way.
If you can find a group named A from a fixed set filtered by some conditions, all elements in this group A can find a greater element from a fix set. On the other hands, other elements which does not belong to the group A cannot find any element which is greater than itself, which also means that those other element are the greatest.
If you can find a group named B from a fixed set filtered by some conditions, all elemments in this group B can find a smaller element from a fix set. On the other hands, other elements which does not belong to the group B cannot find any element which is smaller than itself, which also mean that those elements are the smallest.
Solution
I would like to find the latest/newest assessments of all people. Let do it step by step and analyze:
The over all data set of a person who own id is 1. As you can see, for a single person, there are many assessments has been done by him/her. We have to find out the latest assessment answers of each assessment id. For example: assessment answers with id: 1, 7, 8, 9; the person has finished this assessment_id 2 four times.
The fixed set we are talking about is starting from id 1 -> 12, however, our group contain 1, 7, 8, 10. 1, 7, 8, 10 can find greater element for instance:
The inserted_at(id_1) is smaller than inserted_at(id_7). For those elements which does not belong to this group cannot find greater element, because they are greatest ones. The other elements should include 2, 3, 4, 5, 6, 9, 11, 12. The previous query used join phrase as a consequence, it remove all unsatisfied element for condition aa.insrted_at < ab.inserted_at. On the other hands, left join takes satisfied and unsatisfied records.
Q: Can we place the condition aa.inserted_at < ab.inserted_at under where phrase instead of under lelft join on phrase, and why?
A: No, if we put the condition aa.inserted_at < ab.inserted_at under the where phrase, we can only get a group of not-greatest elements
Q: If I use left join in this query, why dont I get a combine of satisfied and unsatisfied records:
A: This is how the query look like and its result set.
The condition I am talking here is aa.person_id = ab.person_id and aa.assessment_id = ab.assessment_id
Satisfied condition is aa.person_id == ab.person_id and aa.assessment_id == ab.assessment_id
Unsatisfied condition is aa.person_id != ab.person_id or aa.assessment_id != ab.assessment_id
Why the record that are not satisfied exist in the result set. Hmm, that’s a question I am think about. Personally, I think the developers of postgres did make an exception, hardcode perhap if people use equal in the join expression.
Since the documentation of Opera has been out of date, this article is all about installing flash plugin manually, I strongly believe that this can help you in any version of Opera or any operating system. In my free time, I have spent time researching on the resouce files of Opera and trace the directory that Opera use to read the flashplayer.so.
As you can guess, we gonna download flash plugin from its official site then extract into any of these directory such as /usr/lib/adobe-flashplugin/. You need to extract two files including libpepflashplayer.so and manifiest.json, it’s a must to copy manifest.json along with the libpepflashplayer.so. Remember to set extracted files with appropriate permission (chmod command).
1. How to specify the layout when render() in controllers
There is an option in render/3 method, source
In the below example, I did specify the layout, the layout will be located at @conn.assigns[:layout], so as :id
And then, within scope, add the pipeline via pipe_through. Here is an example.
scope"/",ImageQuickSharedopipe_through[:browser,:empty_layout]# Use the default browser stackget"/",PageController,:indexget"/image",ImageController,:showend
This post is all about how to change redirect url after devise update password
(or any?). By default, devise after change password successfully, it will
redirect to the root url. There are step you have to do to change the redirect
path.
Make devise controllers Or generate using command rails g
devise:controllers user
After generating, because I want to change the redirect url after changing
password. The only file I concern is passwords_controller.rb, the method you
have to override is after_resetting_password_path_for, within this method, you
have to declare your favorite redirect url.
In Phoenix web framework, there is a share directory /priv. By default, it
will only public css,js,images,fonts directory. However, If you want to share
a new directory to save upload image for example, you have to end_point file at
/lib/app_name/end_point.ex . Look at plug Plug.Static, the only: macro
declares which directory, files could be public. Simply, you have to append your
directory name at only:line.
This is my configuration to add a directory named avatar public. This directory
is under /priv/static.
plugPlug.Static,at:"/",from::blog_phoenix,gzip:false,only:~w(avatars css fonts images js favicon.ico robots.txt)### Other no need configurationend
defexport_search_resultrequire'spreadsheet'require'stringio'Spreadsheet.client_encoding='UTF-8'book=Spreadsheet::Workbook.newsheet1=book.create_worksheet#YOUR DATA PROCESSOR HEREfile_name="abc.xls"spreadsheet=StringIO.newbook.writespreadsheetsend_data(spreadsheet.string,:filename=>file_name,:type=>"application/vnd.ms-excel")end