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Database Structure for Tree Data Structure
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Have a look at Managing Hierarchical Data in MySQL. It discusses two approaches for storing and managing hierarchical (tree-like) data in a relational database.
The first approach is the adjacency list model, which is what you essentially describe: having a foreign key...
How can I merge properties of two JavaScript objects dynamically?
...d use object spread:
let merged = {...obj1, ...obj2};
merged is now the union of obj1 and obj2. Properties in obj2 will overwrite those in obj1.
/** There's no limit to the number of objects you can merge.
* Later properties overwrite earlier properties with the same name. */
const allRules = ...
Why should I capitalize my SQL keywords? [duplicate]
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So does MySQL, and for good and for bad (mostly bad:-), many developers first exposure to SQL is through MySQL.
– Paul Tomblin
Mar 4 '09 at 13:41
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How to ignore xargs commands if stdin input is empty?
...t;#args>, -i, and -I <string>:
ls /empty_dir/ | xargs -n10 chown root # chown executed every 10 args or fewer
ls /empty_dir/ | xargs -L10 chown root # chown executed every 10 lines or fewer
ls /empty_dir/ | xargs -i cp {} {}.bak # every {} is replaced with the args from one input line
ls /...
ASP.NET 2.0 - How to use app_offline.htm
I've read about the app_offline.htm file which can be placed within the root of a .NET 2.0 application which will in essence shut down the application and disable any other pages from being requested.
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How to pass arguments to a Button command in Tkinter?
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Example GUI:
Let's say I have the GUI:
import tkinter as tk
root = tk.Tk()
btn = tk.Button(root, text="Press")
btn.pack()
root.mainloop()
What Happens When a Button Is Pressed
See that when btn is pressed it calls its own function which is very similar to button_press_handle in t...
AWS ssh access 'Permission denied (publickey)' issue [closed]
...ec2-user instead of ubuntu.
Most EC2 Linux images I've used only have the root user created by default.
See also: http://www.youtube.com/watch?v=WBro0TEAd7g
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CocoaPods Errors on Project Build
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However, when I go to the target's User-Defined Build Settings, the PODS_ROOT entry is either entirely missing or is empty for one or more configurations. Which causes the following error on build:
The simplest fix is to close the project in Xcode and reopen it.
If you go to the target's Build...
Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign
...ords can generate duplicate primary keys which will cause this error.
SQL unions can spell trouble. I modified one table adapter by adding a ‘please select an employee’ record preceding the others. For the other fields I provided dummy data including, for example, strings of length one. The DAL...
Does a UNIQUE constraint automatically create an INDEX on the field(s)?
...email, user_id) is enough, you don't need a separate index on email only - MySQL can use leftmost parts of a composite index. There may be some border cases where the size of an index can slow down your queries, but you should not worry about them until you actually run into them.
As for testing in...