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What's wrong with nullable columns in composite primary keys?
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Primary keys are for uniquely identifying rows. This is done by comparing all parts of a key to the input.
Per definition, NULL cannot be part of a successful comparison. Even a comparison to itself (NULL = NULL) will fail. This means a key containing NULL would not work.
Additonally, NULL is al...
How do I use reflection to invoke a private method?
There are a group of private methods in my class, and I need to call one dynamically based on an input value. Both the invoking code and the target methods are in the same instance. The code looks like this:
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Impossible to Install PG gem on my mac with Mavericks
I'm trying to install the pg gem in order to work again with my rails projects. But I get this error:
26 Answers
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What does numpy.random.seed(0) do?
... I'm not very familiar with NumPy's random state generator stuff, so I'd really appreciate a layman's terms explanation of this.
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Calling closure assigned to object property directly
...sn't work on a StdClass.
Before PHP7, you'd have to implement the magic __call method to intercept the call and invoke the callback (which is not possible for StdClass of course, because you cannot add the __call method)
class Foo
{
public function __call($method, $args)
{
if(is_...
App Inventor 2 倒计时与计时器教程 - Clock组件详解 · App Inventor 2 中文网
...tantInTime（时间瞬间）对象。
when Screen1.Initialize() {
标签_时间.Text = 计时器1.FormatDateTime(计时器1.Now(), "yyyy-MM-dd HH:mm:ss")
}
常用日期时间格式模式：
模式
示例输出
说明
yyyy-MM-dd
2025-01-15
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How to add http:// if it doesn't exist in the URL?
...hat went on a swim and came back as a fish with the mindset to stop you at all costs from doing and things that might hurt you. There are so many people in the world, and you know, you have this incredible ideas and what you think is missing is motivation, But that is not true. because the way that ...
App Inventor 2 LLMAI2Ext 自研拓展：接入DeepSeek、Kimi、通义千问...等国...
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when Screen1.Initialize() {
DeepSeek1.StreamMode = false
}
when 按钮_发送.Click() {
标签_回答.Text = "思考中…"
DeepSeek1.Chat(文本输入框_提问.Text)
}
when DeepSeek1.GotText(text) {
标签_回答.Text = text
}
2. 流式输出，边生成边显示
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How do I fix PyDev “Undefined variable from import” errors?
...ncing the same issue with latest Eclipse and PyDev. I can navigate between all modules, so why code-analysis can't do the same?
– Adam
Sep 3 '14 at 11:41
3
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What does = +_ mean in JavaScript
I was wondering what the = +_ operator means in JavaScript. It looks like it does assignments.
12 Answers
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