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How to create and handle composite primary key in JPA
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You can make an Embedded class, which contains your two keys, and then have a reference to that class as EmbeddedId in your Entity.
You would need the @EmbeddedId and @Embeddable annotations.
@Entity
public class YourEntity {
@EmbeddedId
private MyKey myKey;
@Column(name ...
Why is 128==128 false but 127==127 is true when comparing Integer wrappers in Java?
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When you compile a number literal in Java and assign it to a Integer (capital I) the compiler emits:
Integer b2 =Integer.valueOf(127)
This line of code is also generated when you use autoboxing.
valueOf is implemented such that certain numbers are "pooled", and i...
insert a NOT NULL column to an existing table
...Null-able column, then update your table column with valid not null values and finally ALTER column to set NOT NULL constraint:
ALTER TABLE MY_TABLE ADD STAGE INT NULL
GO
UPDATE MY_TABLE SET <a valid not null values for your column>
GO
ALTER TABLE MY_TABLE ALTER COLUMN STAGE INT NOT NULL
GO
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Creating a daemon in Linux
In Linux I want to add a daemon that cannot be stopped and which monitors filesystem changes.
If any changes are detected, it should write the path to the console where it was started plus a newline.
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Android: Scale a Drawable or background image?
... like this:
<?xml version="1.0" encoding="utf-8"?>
<bitmap xmlns:android="http://schemas.android.com/apk/res/android"
android:gravity="center"
android:src="@drawable/list_bkgnd" />
Then it will be centered in the view if used as background. There are also other flags: http://d...
Formatting code in Notepad++
... Delete to start of line
Ctrl-Shft-Delete Delete to end of line
Ctrl-U Convert to lower case
Ctrl-Shft-U Convert to UPPER CASE
Ctrl-B Go to matching brace
Ctrl-Shft-R Start to record /Stop recording the macro
Ctrl-Shft-P Play recorded macro
Ctrl-Q Block comment/uncomment
Ctrl-Shft-Q Stream com...
How to capitalize the first letter in a String in Ruby
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Thank you just what I was looking for, useful for converting headings to 'sentence case'
– Good Lux
Sep 23 '17 at 11:12
2
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How to fix “Incorrect string value” errors?
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The table and fields have the wrong encoding; however, you can convert them to UTF-8.
ALTER TABLE logtest CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_ci;
ALTER TABLE logtest DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;
ALTER TABLE logtest CHANGE title title VARCHAR(100) ...
boost多索引容器multi_index_container实战 - C/C++ - 清泛网 - 专注C/C++及内核技术
...创建一些结构：
// 课程
struct Course
{
unsigned int course_num; // 课程编号
unsigned int course_hour; // 课时
std::string course_name; // 课程名
// 课程枚举
enum CourseNum_Enum
{
Cours...
Generate a random alphanumeric string in Cocoa
I want to call a method, pass it the length and have it generate a random alphanumeric string.
20 Answers
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