大约有 30,000 项符合查询结果（耗时：0.0462秒） [XML]
What does inverse_of do? What SQL does it generate?
...the documentation, it seems like the :inverse_of option is a method for avoiding SQL queries, not generating them. It's a hint to ActiveRecord to use already loaded data instead of fetching it again through a relationship.
Their example:
class Dungeon < ActiveRecord::Base
has_many :traps, :in...
How do I iterate over a JSON structure? [duplicate]
... four:4, five:5 };
jQuery.each(arr, function() {
$("#" + this).text("My id is " + this + ".");
return (this != "four"); // will stop running to skip "five"
});
jQuery.each(obj, function(i, val) {
$("#" + i).append(document.createTextNode(" - " + val));
});
...
jQuery get selected option value (not the text, but the attribute 'value')
...he option.
$('select[name=selector] option').filter(':selected').val()
Side note: Using filter is better then using :selected selector directly in the first query.
If inside a change handler, you could use simply this.value to get the selected option value. See demo for more options.
//ways...
JavaScript null check
... in JavaScript. However, it's always safe to test if the typeof(x) is the string "undefined", even if "x" is not a declared variable:
alert(typeof(x) === 'undefined'); // true
Also, variables can have the "undefined value" if they are not initialized:
var y;
alert(typeof(y) === 'undefined'); //...
What are the differences between Generics in C# and Java… and Templates in C++? [closed]
... either hard-coding the actual class in, or using interfaces. For example:
string addNames<T>( T first, T second ) { return first.Name() + second.Name(); }
That code won't compile in C# or Java, because it doesn't know that the type T actually provides a method called Name(). You have to tell...
The relationship could not be changed because one or more of the foreign-key properties is non-nulla
I am getting this error when I GetById() on an entity and then set the collection of child entities to my new list which comes from the MVC view.
...
SQL Add foreign key to existing column
...
Error indicates that there is no UserID column in your Employees table. Try adding the column first and then re-run the statement.
ALTER TABLE Employees
ADD CONSTRAINT FK_ActiveDirectories_UserID FOREIGN KEY (UserID)
REFERENCES ActiveDirectories(id);
...
How to enter in a Docker container already running with a new TTY
...le to access the container from another shell in order to "poke around" inside it and examine the files. At the moment, if I attach to the container, I am left looking at the Apache daemon and cannot run any commands.
...
When NOT to use yield (return) [duplicate]
...eason
// (a new state machine needs to be generated)
public IEnumerable<string> GetKeys()
{
foreach(string key in _someDictionary.Keys)
yield return key;
}
// DO this
public IEnumerable<string> GetKeys()
{
return _someDictionary.Keys;
}
Avoid using yield return when yo...
When to use %r instead of %s in Python? [duplicate]
...
An important difference when using these in string formatting is that %r will also include the delimiting quotes. print('Text: %r' % 'Hello') -> Text: 'Hello', print('Text: %s' % 'Hello') -> Text Hello
– Markus
Jan 10 '18 at...