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@UniqueConstraint annotation in Java
...rite
@Column(unique=true)
String username;
The @UniqueConstraint annotation is for annotating multiple unique keys at the table level, which is why you get an error when applying it to a field.
References (JPA TopLink):
@UniqueConstraint
@Column
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How to dismiss ViewController in Swift?
...s a ViewController in swift by calling dismissViewController in an IBAction
20 Answers
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What's the difference between QMainWindow, QWidget and QDialog?
... to be shown as a window. It will always appear in a window, and has functions to make it work well with common buttons on dialogs (accept, reject, etc.).
QMainWindow is designed around common needs for a main window to have. It has predefined places for a menu bar, a status bar, a toolbar, and o...
How do I remove a MySQL database?
You may notice from my last question that a problem caused some more problems, Reading MySQL manuals in MySQL monitor?
6 A...
Checking if a folder exists using a .bat file [closed]
...he name of your file.
For a directory look at this https://jeffpar.github.io/kbarchive/kb/065/Q65994/
C:
IF NOT EXIST C:\WIN\ GOTO NOWINDIR
CD \WIN
:NOWINDIR
trailing backslash ('\') seems to be enough to distinguish between directories and ordinary files.
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Cordova 3.5.0 Install Error- Please Install Android Target 19
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Android SDK is not your target Android version. Target Android version 19 is the API level for android Kitkat.So in you SDK manager check if you have Android 4.4.2(API 19) installed. If you want your target API version to be different then change it in ANdroidManifest...
What is Mocking?
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Prologue: If you look up the noun mock in the dictionary you will find that one of the definitions of the word is something made as an imitation.
Mocking is primarily used in unit testing. An object under test may
have dependencies on other (complex) objects. To isolate the...
Why does Apple recommend to use dispatch_once for implementing the singleton pattern under ARC?
...ync() is synchronous). The use of dispatch_once() replaces the following idiom:
+ (MyClass *)sharedInstance {
static MyClass *sharedInstance;
@synchronized(self) {
if (sharedInstance == nil) {
sharedInstance = [[MyClass alloc] init];
}
}
return sharedInst...
记一次MongoDB性能问题 - 大数据 & AI - 清泛网 - 专注C/C++及内核技术
...avoid performance problems: numactl –interleave=all mongod [other options]
当时我并不太清楚NUMA是什么东西，所以没有处理，只是把问题反馈给了运维人员，后来知道运维人员也没有理会这茬儿，所以问题的序幕就这样拉开了。
迁移工作...
“Could not find bundler” error
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if you create a new applocation - rails new and if you get this error?
– AMIC MING
Mar 19 '13 at 0:35
2
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