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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...
Setting CSS pseudo-class rules from JavaScript
... can do it by altering the stylesheet, for example by adding the rule:
#elid:hover { background: red; }
assuming each element you want to affect has a unique ID to allow it to be selected.
In theory the document you want is http://www.w3.org/TR/DOM-Level-2-Style/Overview.html which means you can...
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 ...
convert ArrayList to JSONArray
...NArray(list);
References:
jsonarray constructor:
http://developer.android.com/reference/org/json/JSONArray.html#JSONArray%28java.util.Collection%29
collection:
http://developer.android.com/reference/java/util/Collection.html
...
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...
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 ...
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
...
What is a “slug” in Django?
...
A "slug" is a way of generating a valid URL, generally using data already obtained. For instance, a slug uses the title of an article to generate a URL. I advise to generate the slug by means of a function, given the title (or another piece of data), rather than...
How to use ArrayAdapter
...iew;
}
public MyClassAdapter(Context context, int textViewResourceId, ArrayList<MyClass> items) {
super(context, textViewResourceId, items);
}
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
conve...