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Run a callback only if an attribute has changed in Rails
...
Rails 5.1+
class Page < ActiveRecord::Base
before_save :do_something, if: :will_save_change_to_status_id?
private
def do_something
# ...
end
end
The commit that changed ActiveRecord::Dirty is here: https://github.com/rails/rails/commit/16ae3db5a5c6a08383b974ae...
Zip lists in Python
...x. list, string, tuple, dictionary)
Output (list)
1st tuple = (element_1 of numbers, element_1 of letters)
2nd tuple = (e_2 numbers, e_2 letters)
…
n-th tuple = (e_n numbers, e_n letters)
List of n tuples: n is the length of the shortest argument (input)
len(numbers) =...
What is the purpose of the word 'self'?
...
But in __init__(self) method, it accepts self, then even without creating the object, how does it refer to itself?
– saurav
Jan 28 '18 at 10:10
...
When to use dynamic vs. static libraries
...t virtual address. DLL certainly supports this.
– dma_k
Oct 2 '10 at 12:35
21
@dma_k: Windows DLL...
How can I get the MAC and the IP address of a connected client in PHP?
...
Server IP
You can get the server IP address from $_SERVER['SERVER_ADDR'].
Server MAC address
For the MAC address, you could parse the output of netstat -ie in Linux, or ipconfig /all in Windows.
Client IP address
You can get the client IP from $_SERVER['REMOTE_ADDR']
C...
ObservableCollection not noticing when Item in it changes (even with INotifyPropertyChanged)
...leCollection<EntityViewModel> ContentList
{
get { return _contentList; }
}
public CollectionViewModel()
{
_contentList = new ObservableCollection<EntityViewModel>();
_contentList.CollectionChanged += ContentCollectionChanged;
}
public v...
Programmatically retrieve memory usage on iPhone
...icture of usage over-all.
#import <mach/mach.h>
// ...
void report_memory(void) {
struct task_basic_info info;
mach_msg_type_number_t size = TASK_BASIC_INFO_COUNT;
kern_return_t kerr = task_info(mach_task_self(),
TASK_BASIC_INFO,
...
Why is it impossible to override a getter-only property and add a setter? [closed]
... derivation, my code may break. e.g.
public class BarProvider
{ BaseClass _source;
Bar _currentBar;
public void setSource(BaseClass b)
{
_source = b;
_currentBar = b.Bar;
}
public Bar getBar()
{ return _currentBar; }
}
Since Bar cannot be set as per the BaseClass interface,...
Python Dictionary Comprehension
...a subclass of dict which works somewhat like a defaultdict if you override __missing__:
>>> class KeyDict(dict):
... def __missing__(self, key):
... #self[key] = key # Maybe add this also?
... return key
...
>>> d = KeyDict()
>>> d[1]
1
>>> d[2]
...
How to send multiple data fields via Ajax? [closed]
...ries[0] = 'ga';
countries[1] = 'cd';
after that you can do like:
var new_countries = countries.join(',')
after:
$.ajax({
type: "POST",
url: "Concessions.aspx/GetConcessions",
data: new_countries,
...
This thing work as JSON string format.
...