migration

问题 So I want to know whether we can write a new migration just to set default value of a field,which is already created. I know how to write edit the old migration and set its default value. I want to do this because I have done so many migrations and I cant roll back now and edit that file. And also, Is there any way to rollback to a particular migration? Thanks in advance 回答1: Run rails g migration add_default_value_to_table then in the migration file def up change_column :table_name, :column

问题 So apparently now I get this weird error when I want to migrate my database {"error":{"type":"Symfony\\Component\\Debug\\Exception\\FatalErrorException","message":"Class '' not found","file":"C:\\xampp\\htdocs\\l4crm\\vendor\\laravel\\framework\\src\\Illuminate\\Database\\Migrations\\Migrator.php","line":301}}[Finished in 1.3s] Everything used to work of course and it doesn't matter which files I try to migrate (I tried only migrating one table, then another, they all give the same error) Any

问题 I have a save override method in my model class, which generates a new slug each time an object is saved. def save(self, *args, **kwargs): if self.column2: self.slug = slugify(self.column1 + " " + self.column2) else: self.slug = slugify(self.column1) print slug super(MyModel, self).save(*args, **kwargs) When I try to create a new object by logging into the python shell, I see the save method is being invoked. python manage.py shell >>> MyModel(column1="test",column2="2015").save() slug is

问题 I created a model with an attribute "name" but I want to change it to "username". Everything I've read about database migrations involves creating a class or some complicated stuff. All I want to do is the equivalent of "UPDATE TABLE" in SQL. How do you run a one-time database migration to change this? I'm guessing it'd involve rails console and then some command? 回答1: First: rails g migration rename_name_column_to_username Then in the generated rename_name_column_to_username.rb migration

问题 I'm nearling completion of my first CakePHP-driven website and just saw they're already working on CakePHP 2.0 (not the stable release yet). My questions: Is it incredibly time consuming to move to a new version of CakePHP (when it becomes the "stable" release that is)? I know they have migration guides, but - I've never used a framework before, so I've never had to migrate anything. Do you migrate your code for existing projects, or leave it as is and use the new stable version for future

问题 Is there a standard way to do database schema migrations on Android? For example, user installs newer version of my Android app but the new version needs to make updates to the database schema (and wiping the user's database and starting over is not an option!). So I need to run some ALTER statements and/or copy tables the first time my new version runs. 回答1: Yes SQLiteOpenHelper has support for migrating between different versions of DB schemas. Upgrading is done by implementing public

问题 I have code from PowerBuilder 5 that can't be built. The compiler just stops before it is done without any error codes. I would like to upgrade the code to the recent version of PowerBuilder but there are some intermediate versions of PowerBuilder that have binary dependencies to an old Microsoft java dll that Microsoft no longer can distribute due to some court case. So, is there a way to get my code running in a newer environment? /johan/ 回答1: Firstly, you don't need to use "intermediate

问题 If you want to migrate Struts1 to Struts2, you can leave the JSP implementation in Struts1 and rewrite the action class in Struts2? Can you add in web.xml both configurations for Struts1 and Struts2? 回答1: You have to rewrite both action classes and JSP, however you can reuse your business services if they are exist on the service layer. The same is for persistence layer. Note, if you can leave JSP implementation, then you should replace them with something that will work on the view layer. It

问题 Hello I read Django tutorials and I have an error related to specific sha3_224 hash function during the migration process. How to solve this problem? Thank you. (venv) linuxoid@linuxoid-ThinkPad-L540:~/myprojects/myproject$ python manage.py makemigrations ERROR:root:code for hash sha3_224 was not found. Traceback (most recent call last): File "/home/linuxoid/myprojects/venv/lib/python3.6/hashlib.py", line 121, in __get_openssl_constructor f = getattr(_hashlib, 'openssl_' + name)

问题 I get the following error message: heroku db:pull --debug postgres://USERNAME:PASSWORD@localhost/test Loaded Taps v0.3.23 Warning: Data in the database 'postgres://USERNAME:PASSWORD@localhost/test' will be overwritten and will not be recoverable. Receiving schema Unable to fetch tables information from http://heroku:foo9dsfsdfsdb465ar@taps19.heroku.com. Please check the server log. The command above does not produce any messages in the log that can be viewed using 'heroku logs'. Any idea what