大约有 43,000 项符合查询结果（耗时：0.0585秒） [XML]
Ruby on Rails Callback, what is difference between :before_save and :before_create?
Could you explain in detail what the :before_save and :before_create Ruby on Rails callbacks are, and what they have to do with Rails validations? Does validation occur after :before_save or :before_create ?
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How to add 'ON DELETE CASCADE' in ALTER TABLE statement
...ON DELETE CASCADE to an already existing constraint. You will have to drop and re-create the constraint. The documentation shows that the MODIFY CONSTRAINT clause can only modify the state of a constraint (i-e: ENABLED/DISABLED...).
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What is the fundamental difference between WebSockets and pure TCP?
I've read about WebSockets and I wonder why browser couldn't simply open trivial TCP connection and communicate with server like any other desktop application. And why this communication is possible via websockets?
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Amazon EC2, mysql aborting start because InnoDB: mmap (x bytes) failed; errno 12
.... Since Micro instances have only 613MB of memory, MySQL crashed every now and then. After a long search about MySQL, Micro Instance and Memory Managment I found out there is no default SWAP space for Micro instance. So if you want to avoid the crash you may need to setup a swap space for your micro...
'float' vs. 'double' precision
... in C use IEEE 754 encoding.
This type of encoding uses a sign, a significand, and an exponent.
Because of this encoding, many numbers will have small changes to allow them to be stored.
Also, the number of significant digits can change slightly since it is a binary representation, not a decimal ...
JavaScript: What are .extend and .prototype used for?
I am relatively new to JavaScript and keep seeing .extend and .prototype in third party libraries I am using. I thought it had to do with the Prototype javascript library, but I am beginning to think that is not the case. What are these used for?
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Failed to load resource: net::ERR_INSECURE_RESPONSE
...uming your frame's URL is https://www.domain.com, open a new tab in chrome and go to https://www.domain.com.
Chrome will ask you to accept the SSL certificate. Accept it.
Then, if you reload your page with your frame, you could see that now it works
The problem as you can guess, is that each visit...
How to order citations by appearance using BibTeX?
...erwise
Use the makebst (link) tool to design your own bibliography style
And my personal recommendation:
Use the biblatex package (link). It's the most complete and flexible bibliography tool in the LaTeX world.
Using biblatex, you'd write something like
\documentclass[12pt]{article}
\usepack...
Compare two MySQL databases [closed]
...es I've found running mysqldump on both databases with the --skip-comments and --skip-extended-insert options to generate SQL scripts, then running diff on the SQL scripts works pretty well.
By skipping comments you avoid meaningless differences such as the time you ran the mysqldump command. By us...
Are there any free Xml Diff/Merge tools available? [closed]
...Diff3 is not XML specific, but it is free. It does a nice job of comparing and merging text files.
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