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Run a callback only if an attribute has changed in Rails
...eRecord::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/16ae3db5a5c6a08383b974ae6c96faac5b4a3c81
Here is a blog post on these change...
With MySQL, how can I generate a column containing the record index in a table?
... @smhnaji MySQL requires that every "derived table" is given a name. I decided to call it "r" :) ... It has little purpose in this case, but you'd normally use it to reference attributes of the derived table, as if it was a real table.
– Daniel Vassallo
Feb 27...
How do I invert BooleanToVisibilityConverter?
... }
if (parameter != null)
{
if (bool.Parse((string)parameter))
{
flag = !flag;
}
}
if (flag)
{
return Visibility.Visible;
}
else
{
return Visibility.Collapse...
What does $@ mean in a shell script?
... join all arguments by single spaces as well and
# will then split the string as the shell does on the command
# line, thus it will split an argument containing spaces into
# several arguments.
Example: Calling
wrapper "one two three" four five "six seven"
will result in:
"$@": ...
JavaScript property access: dot notation vs. brackets?
...n the obvious fact that the first form could use a variable and not just a string literal, is there any reason to use one over the other, and if so under which cases?
...
How do I concatenate two arrays in C#?
...ys instead of lists. eg System.IO.Directory.GetFiles() returns an array of strings.
– orion elenzil
Jan 7 '16 at 17:55
4
...
Can you create nested WITH clauses for Common Table Expressions?
... Stating that this is not nested, just because query 2 is not inside the parenthesis of query 1, sounds like a weak argument. I think it's nested (not recursively nested), because query 2 uses the result of query 1, which occurs with nesting too. Is defined that nesting can only be when a ...
Why is this jQuery click function not working?
...tion() {
$("#clicker").click(function () {
alert("Hello!");
$(".hide_div").hide();
});
});
As jQuery documentation states: "A page can't be manipulated safely until the document is "ready." jQuery detects this state of readiness for you. Code included inside $( document ).ready() will ...
What's the difference between lists and tuples?
... tuples being immutable there is also a semantic distinction that should guide their usage. Tuples are heterogeneous data structures (i.e., their entries have different meanings), while lists are homogeneous sequences. Tuples have structure, lists have order.
Using this distinction makes code more...
How To Save Canvas As An Image With canvas.toDataURL()?
...
This works great... But in Android (Default browser in Galaxy S3) it just doesn't download the image, but i get the message "Downloading..." forever.
– Habrashat
Jul 28 '14 at 6:05
...