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Fortnightly Programming Q&A Thread

Automatically posted September 29, 2020

General Programming Q&A thread! Ask any questions about programming, answer the questions of other users, or post suggestions for future threads.

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Here is my schema:

```sql
CREATE TABLE article_to_warehouse (
  article_id   INTEGER
, warehouse_id INTEGER
)
;
```

How do I add a `UNIQUE` constraint?

1 comment

Gyrfalcon
October 13, 2020
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Hello! I've been getting back into personal projects by trying out Julia on some old Advent of Code problems and retooling some personal projects. I did a writeup of a question I have that really...
Hello! I've been getting back into personal projects by trying out Julia on some old Advent of Code problems and retooling some personal projects. I did a writeup of a question I have that really gets at moving from object oriented languages (Python/C++) to Julia, where multiple dispatch is the name of the game, along with grokking the nature of including other source files in Julia. If you know anything about that, I'd love it if you could post an answer here, or on the Julia forum. I'll also copy the post I made here for reference:

Hello! I am a newcomer to Julia and I am trying to recreate something that I worked a bit on in Python in Julia, because I think Julia will be the better language overall for numerical performance. However, I am trying to do something that I am not sure Julia is suited for before I can get to that numerical aspect.

The code needs to interact with several outside sources of data, like databases, web APIs, etc. What I would like is for a configuration file to be able to define which files to import for each of these sources. Then, the program will import those source files and use the functions within to download data, store it away, etc. In Python I would do this with an abstract base class, and dynamically import the module based on the name saved in the configuration file. In Julia, I am not so sure. It seems there are a few options possible with metaprogramming, but I am not sure they fit exactly into what I imagine. Maybe something like the following as a minimum (but not working!) example would help:
```
# Main file
include("ConfigImport.jl")

function main()
    imported_file = ConfigImport.import_config() # where imported file is a reference to OtherFile
    imported_file.do_stuff()
end

main()

# ConfigImport.jl

module ConfigImport

using TOML

function import_config()

config_data = nothing
    try
        config_data = TOML.parsefile("config/config.toml")

    catch e
        if isa(e, SystemError)
            println("It appears the config file is missing!")
        elseif isa(e, TOML.ParserError)
            println("It appears there is something wrong with the format of the config file!")
        else
            throw(e)
        end
    end

    include(config_data["OtherFile"] * ".jl")
    return Symbol(config_data["OtherFile"])
end
end

# OtherFile.jl

module OtherFile

function do_stuff()
    println("Doing some stuff!")
end

end
```
I feel like there has to be a better design pattern or a use of macros to accomplish what I am trying to do, I just have no idea what that might be.