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Add Foreign Key to existing table
...
To add a foreign key (grade_id) to an existing table (users), follow the following steps:
ALTER TABLE users ADD grade_id SMALLINT UNSIGNED NOT NULL DEFAULT 0;
ALTER TABLE users ADD CONSTRAINT fk_grade_id FOREIGN KEY (grade_id) REFERENCES grades(id);
...
How to check if an int is a null
...er to be able to be null, you need to use Integer instead of int.
Integer id;
String name;
public Integer getId() { return id; }
Besides the statement if(person.equals(null)) can't be true, because if person is null, then a NullPointerException will be thrown. So the correct expression is if (pe...
how to break the _.each function in underscore.js
...s the native forEach method's behavior, and the native forEach doesn't provide to escape the loop (other than throwing an exception).
However, all hope is not lost! You can use the Array.every method. :)
From that link:
every executes the provided callback function once for each element presen...
Selecting all text in HTML text input when clicked
...ument for the click handler. Better yet, you could eliminate the getElementById entirely and pass this as an argument.
– Asad Saeeduddin
Dec 14 '12 at 23:05
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CSS opacity only to background color, not the text on it? [duplicate]
...ppens when you need your #block opac background placement to be determined by your text? For instance: hovering over a promo block brings up text half the size of the promo block. The #block layer won't respond to the text height.
– Ben Sewards
Oct 23 '14 at 21...
How does inline Javascript (in HTML) work?
...lick Me</a>
<script type="text/javascript">
document.getElementById('click_me').addEventListener("click", function(event) {
(function(event) {
alert(this);
}).call(document.getElementById('click_me'), event);
});
</script>
Inline event handlers set this equal to t...
Transparent ARGB hex value
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Transparency is controlled by the alpha channel (AA in #AARRGGBB). Maximal value (255 dec, FF hex) means fully opaque. Minimum value (0 dec, 00 hex) means fully transparent. Values in between are semi-transparent, i.e. the color is mixed with the backg...
What are the differences between vector and list data types in R?
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As someone who's just gotten into R, but comes from a C/Java/Ruby/PHP/Python background, here's how I think of it.
A list is really an array + a hashmap. It's a PHP associative array.
> foo = list(bar='baz')
> foo[1]
'baz'
> foo$bar
'baz'
> foo[['bar']]
'baz'
A vector is ...
怎么往SetTimer的回调函数传递参数 - C/C++ - 清泛网 - 专注C/C++及内核技术
...Proc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
int wmId, wmEvent;
PAINTSTRUCT ps;
HDC hdc;
switch (message)//message就是消息号
{
case WM_COMMAND:
...
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;...
Django Reverse with arguments '()' and keyword arguments '{}' not found
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You have to specify project_id:
reverse('edit_project', kwargs={'project_id':4})
Doc here
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