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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...
How to include jar files with java file and compile in command prompt
...r your dependency jar files as shown below:
set classpath=C:\Users\sarath_sivan\Desktop\jars\servlet-api.jar; C:\Users\sarath_sivan\Desktop\jars\spring-jdbc-3.0.2.RELEASE; C:\Users\sarath_sivan\Desktop\jars\spring-aop-3.0.2.RELEASE;
Now, you may compile your java file. (command: javac YourJavaFile...
Print multiple arguments in Python
... isn't a function in Python 2. You can, however, import this behavior from __future__:
from __future__ import print_function
Use the new f-string formatting in Python 3.6:
print(f'Total score for {name} is {score}')
sha...
Checking if a double (or float) is NaN in C++
...d portable solution. You can even test for -ffast-math by testing for the __FAST_MATH__ macro and switch to a different implementation in that case (e.g. use unions and bit twiddling).
– Adam Rosenfield
Mar 27 '11 at 23:45
...
Can Objective-C switch on NSString?
... @abbood For more information about enum, see the posting NS_ENUM & NS_OPTIONS by Mattt Thompson.
– Basil Bourque
Oct 21 '13 at 21:32
...
How do you add a Dictionary of items into another Dictionary
...
@animal_chin Because we have to implement half of the language ourselves? Yes. Impressed. Don't get me wrong I love operator overloading. I just don't love having to use it for basic features that should be built in.
...
How to determine whether a given Linux is 32 bit or 64 bit?
...
Try uname -m. Which is short of uname --machine and it outputs:
x86_64 ==> 64-bit kernel
i686 ==> 32-bit kernel
Otherwise, not for the Linux kernel, but for the CPU, you type:
cat /proc/cpuinfo
or:
grep flags /proc/cpuinfo
Under "flags" parameter, you will see various value...
Python circular importing?
...if you set them up correctly.
The easiest way to do so is to use import my_module syntax, rather than from my_module import some_object. The former will almost always work, even if my_module included imports us back. The latter only works if my_object is already defined in my_module, which in a cir...
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...
Generate JSON string from NSDictionary in iOS
...ke easier to read).
@interface NSDictionary (BVJSONString)
-(NSString*) bv_jsonStringWithPrettyPrint:(BOOL) prettyPrint;
@end
.
@implementation NSDictionary (BVJSONString)
-(NSString*) bv_jsonStringWithPrettyPrint:(BOOL) prettyPrint {
NSError *error;
NSData *jsonData = [NSJSONSerial...