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differentiate null=True, blank=True in django
When we add a database field in django we generally write:
18 Answers
18
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How do I use jQuery's form.serialize but exclude empty fields
...tween #myForm and :input as it is the descendant operator.
:input matches all input, textarea, select and button elements.
[value!=''] is an attribute not equal filter. The weird (and helpful) thing is that all :input element types have value attributes even selects and checkboxes etc.
Finally to...
Java: how do I get a class literal from a generic type?
Typically, I've seen people use the class literal like this:
8 Answers
8
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CHECK constraint in MySQL is not working
...ySQL Reference Manual says:
The CHECK clause is parsed but ignored by all storage engines.
Try a trigger...
mysql> delimiter //
mysql> CREATE TRIGGER trig_sd_check BEFORE INSERT ON Customer
-> FOR EACH ROW
-> BEGIN
-> IF NEW.SD<0 THEN
-> SET NEW.SD=0;...
How to add a primary key to a MySQL table?
... Column
If you want to add a primary key constraint to an existing column all of the previously listed syntax will fail.
To add a primary key constraint to an existing column use the form:
ALTER TABLE `goods`
MODIFY COLUMN `id` INT(10) UNSIGNED PRIMARY KEY AUTO_INCREMENT;
...
Extracting the last n characters from a string in R
... @mdsumner points out. Consider:
x <- c("some text in a string", "I really need to learn how to count")
substrRight(x, 6)
[1] "string" " count"
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Finding all objects that have a given property inside a collection [duplicate]
...
// put this in some class
public static <T> Collection<T> findAll(Collection<T> coll, Checker<T> chk) {
LinkedList<T> l = new LinkedList<T>();
for (T obj : coll) {
if (chk.check(obj))
l.add(obj);
}
return l;
}
Of course, li...
Printing the last column of a line in a file
...ile | awk '/A1/ {print $NF}'
or without tail, showing the last column of all lines containing A1
awk '/A1/ {print $NF}' file
Thanks to @MitchellTracy's comment, tail might miss the record containing A1 and thus you get no output at all. This may be solved by switching tail and awk, searching ...
Why does this C++ snippet compile (non-void function does not return a value) [duplicate]
...means that the compiler is not obligated provide an error nor a warning usually because it can be difficult to diagnose in all cases. We can see this from the definition of undefined behavior in the draft standard in section 1.3.24 which says:
[...]Permissible undefined behavior ranges from igno...
How to remove text from a string?
...eplace('data-','');
console.log(ret); //prints: 123
Docs.
For all occurrences to be discarded use:
var ret = "data-123".replace(/data-/g,'');
PS: The replace function returns a new string and leaves the original string unchanged, so use the function return value after the replace() c...