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Adding :default => true to boolean in existing Rails column
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change_column is a method of ActiveRecord::Migration, so you can't call it like that in the console.
If you want to add a default value for this column, create a new migration:
rails g migration add_default_value_to_show_attribute
Then in the migration created:
# That's the more generic way t...
remove None value from a list without removing the 0 value
... - it's just for scientific purposes)
>>> from operator import is_not
>>> from functools import partial
>>> L = [0, 23, 234, 89, None, 0, 35, 9]
>>> filter(partial(is_not, None), L)
[0, 23, 234, 89, 0, 35, 9]
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[精华]VC++对话框程序打印及打印预览的实现 - C/C++ - 清泛网 - 专注C/C++及内核技术
...程序文件菜单中会生成两个菜单项分别是打印（标识符ID_FILE_PRINT）和打印预览(标识符：ID_FILE_PRINT_PREVIEW)，展开程序源代码，可以发现，是CVIEW类提供标准打印和打印预览菜单命令的消息处理函数：
设应用程序视图类为CMyView,展...
partial string formatting
...he advanced string formatting methods, similar to the string template safe_substitute() function?
21 Answers
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Longest line in a file
...ing for a simple way to find the length of the longest line in a file. Ideally, it would be a simple bash shell command instead of a script.
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How is the undo tree used in Vim?
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See also :h undo-redo, which lists all the commands and their usage.
There are two ways to traverse the undo tree. One is to go "back in time". g+ and g- will traverse all of the nodes in the tree in chronological or reverse-chronological order (which can...
Build Eclipse Java Project from Command Line
...ore.aptBuild
It uses the jdt apt plugin to build your workspace automatically. This is also known as a 'Headless Build'. Damn hard to figure out. If you're not using a win32 exe, you can try this:
java -cp startup.jar -noSplash -data "D:\Source\MyProject\workspace" -application org.eclipse.jdt....
How do I write the 'cd' command in a makefile?
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It is actually executing the command, changing the directory to some_directory, however, this is performed in a sub-process shell, and affects neither make nor the shell you're working from.
If you're looking to perform more tasks wit...
Facebook API - How do I get a Facebook user's profile image through the Facebook API (without requir
...m/users_unique_url ). How can I accomplish this? Is there a Faceboook API call that fetches a user's profile image URL without the user needing to Allow the application?
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Change MySQL default character set to UTF-8 in my.cnf?
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The above my.cnf settings worked for me as well. Additionally, I had to make sure the table was set properly, such as ALTER TABLE Table CONVERT TO CHARACTER SET utf8 COLLATE utf8_unicode_ci;
– Chris Livdahl
May 26 '11 at 19:26
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