I created a migration in my development to change the column type from integer to date in my client table.
Migration:
class UpdateGradToDate < ActiveRecord::Migration
def change
change_column :clients, :grad_id, :date
end
end
Which worked fine in development. However, once I push it to Heroku, I got the following error message.
PG::DatatypeMismatch: ERROR: column "grad_id" cannot be cast automatically to type date
HINT: You might need to specify "USING grad_id::date".
: ALTER TABLE "clients" ALTER COLUMN "grad_id" TYPE date
I'm not sure how to correct this problem. I'm thinking perhaps using rails console and changing the column type there but I'm not sure if that's the best solution.
I also tried creating a new migration using using this syntax as well
class ChangeDateFormatInMyTable < ActiveRecord::Migration
def up
change_column :clients, :grad_id, :integer
end
def down
change_column :clients, :grad_id, :date
end
end
I'm not really sure what to do at this point.
The issue here is clearly explained by the PostgreSQL error:
column "grad_id" cannot be cast automatically to type date
You are trying to convert a field that stores an integer, into a Date. The field could contain anything, including a value such as 10, 0 or -200. How those value could ever be converted into a Date?
What PostgreSQL is telling you is that you need to help him with the conversion.
Your best way is:
rename grad_id into grad_id_legacy
create a new grad_id Date field
run a script that reads each value from grad_id_legacy and stores the corresponding, converted Date value into grad_id
Related
I initially created a Task model, including a completed_at field set as a time type, with the following migration:
class CreateTasks < ActiveRecord::Migration[7.0]
def change
create_table :tasks do |t|
...
t.time :completed_at
...
t.timestamps
end
end
end
As the project evolved, I converted the completed_at field into a timestamp column, with the following migration:
class ChangeCompletedAtToBeTimestampInTasks < ActiveRecord::Migration[7.0]
def change
change_column :tasks, :completed_at, :timestamp
end
end
The app was working fine locally, with SQLite3, but when I tried to create a build for Heroku with PostgreSQL, with the heroku run rails db:migrate --app my_app_name command, I ran into the following error:
INFO -- : Migrating to ChangeCompletedAtToBeTimestampInTasks (20220713141025)
== 20220713141025 ChangeCompletedAtToBeTimestampInTasks: migrating ============
-- change_column(:tasks, :completed_at, :timestamp)
rails aborted!
StandardError: An error has occurred, this and all later migrations canceled:
PG::DatatypeMismatch: ERROR: column "completed_at" cannot be cast automatically to type timestamp without time zone
HINT: You might need to specify "USING completed_at::timestamp without time zone".
Plus:
Caused by:
ActiveRecord::StatementInvalid: PG::DatatypeMismatch: ERROR: column "completed_at" cannot be cast automatically to type timestamp without time zone
HINT: You might need to specify "USING completed_at::timestamp without time zone".
And:
Caused by:
PG::DatatypeMismatch: ERROR: column "completed_at" cannot be cast automatically to type timestamp without time zone
HINT: You might need to specify "USING completed_at::timestamp without time zone".
Inspired by this 11-year-old thread, I tried to modify the migration that changes the type of the completed_at column from time to timestamp by adding the without time zone option, but it did not solve the issue:
class ChangeCompletedAtToBeTimestampInTasks < ActiveRecord::Migration[7.0]
def change
change_column :tasks, :completed_at, :timestamp without time zone
end
end
Worth mentioning:
I am unsure whether fixing the problem actually requires to set the timestamp column as with time zone or without time zone.
I was not able to find documentation online showing how to apply the without time zone option in a Rails migration, so the code above may be incorrect.
Any thoughts on how to fix this and make the build pass?
Go to pgadmin and try this query it is worked for me.
ALTER TABLE shop_orders ALTER COLUMN appointment_datetime TYPE TIMESTAMP USING appointment_datetime::TIMESTAMP;
Thanks
I am upgrading my rails 3 application to rails 4. And according to the guide I removed this line from my model
serialize :my_serialized_column, ActiveRecord::Coders::Hstore.new({})
but now I am getting the error while looping over :my_serialized_column which was previously hash
undefined method `each' for "":String
Now my question is how do I change the data_type of my column without losing the data I already have
So you can just change the data type of the column from string to hstore.
One thing to keep in mind is you need to cast the data to hstore or you will get the following error
PG::DatatypeMismatch: ERROR: column "my_serialized_column" cannot be cast automatically to type hstore
HINT: You might need to specify "USING my_serialized_column::hstore".
To avoid the error you can specify the casting
class ChangeMySerializedColumnTypeToHstore < ActiveRecord::Migration
def up
change_column_null :my_table, :my_serialized_column, ''
change_column :my_table, :my_serialized_column, "hstore USING my_serialized_column::hstore"
end
def down
change_column :my_table, :my_serialized_column, :string, default: ''
end
end
I am trying to run a rails migration where in I am changing just the column name. So, this rails takes care of keeping the same data type as the old column or tries to make a guess based on the column content?
def change
rename_column :marks, :percent, :percentage
end
The old type was decimal and after migration it still remains decimal.
Just I wanted to know the type was preserved because the existing values were decimal or it was because of the old data type.
rename_column is meant for only simply changing the name of the column without thinking about the datatype.
In the given migration you are changing only the name from percent to percentage so rails doesn't care about the datatype and only changes the name of the column. There is no change in the datatype, it will intact as it is. whether it is decimal, float, string etc.
Yes, rename_column is only renaming the name of column with 3 parameters. change_column would change the type
def change
change_column :marks, :percent, :text
end
I have a Rails 3.2 app that stores zip codes in a user_profiles table. I originally used integer as the data type for zip codes; however, this is obviously wrong since you can't use numbers that start with zero (and some US zip codes do start with zero). Therefore, I need to convert the zip code column AND my production data to string instead. I think this is done with a simple change_column migration, but I don't know the exact code to use when using Postgres. Any help would be much appreciated! My original migration to add the zip code column is below:
class AddZipCodeToUserProfiles < ActiveRecord::Migration
def change
add_column :user_profiles, :zip_code, :integer
end
end
class ChangeZipCodeToString < ActiveRecord::Migration
def change
change_column :user_profiles, :zip_code, :string
end
end
Have you tried that?
At the first migration, I declared on a column content to be string
Activerecord made it to be string(255) according to annotate gem.
After I push the app to heroku, which uses postgres, if I enter in the form in content a string longer than 255 I get the error
PGError: ERROR: value too long for type character varying(255)
Problem is I need that content to contain a string that is extremely long perhaps (free text, could be thousands of chars)
What variable (is string is not appropriate for this) would pg accept?
How do I create a migration to replace the type of that column
thanks
You should use text with Rails if you want a string with no length limit. A migration like this:
def up
change_column :your_table, :your_column, :text
end
def down
# This might cause trouble if you have strings longer
# than 255 characters.
change_column :your_table, :your_column, :string
end
should sort things out. You might want :null => false or some other options on the end of that too.
When you use a string column without an explicit limit, Rails will add an implicit :limit => 255. But if you use text, you'll get whatever arbitrary length string type the database supports. PostgreSQL allows you to use a varchar column without a length but most databases use a separate type for that and Rails doesn't know about varchar without a length. You have to use text in Rails to get a text column in PostgreSQL. There's no difference in PostgreSQL between a column of type text and one of type varchar (but varchar(n) is different). Furthermore, if you're deploying on top of PostgreSQL, there's no reason to use :string (AKA varchar) at all, the database treats text and varchar(n) the same internally except for the extra length constraints for varchar(n); you should only use varchar(n) (AKA :string) if you have an external constraint (such as a government form that says that field 432 on form 897/B will be 23 characters long) on the column size.
As an aside, if you are using a string column anywhere, you should always specify the :limit as a reminder to yourself that there is a limit and you should have a validation in the model to ensure that the limit is not exceeded. If you exceed the limit, PostgreSQL will complain and raise an exception, MySQL will quietly truncate the string or complain (depending on the server configuration), SQLite will let it pass as-is, and other databases will do something else (probably complain).
Also, you should also be developing, testing, and deploying on top of the same database (which will usually be PostgreSQL at Heroku), you should even use the same versions of the database server. There are other differences between databases (such as the behavior of GROUP BY) that ActiveRecord won't insulate you from. You might be doing this already but I thought I'd mention it anyway.
Update: Newer versions of ActiveRecord do understand varchar without a limit so, with PostgreSQL at least, you can say:
change_column :your_table, :your_column, :string, limit: nil
to change a varchar(n) column to varchar. text and varchar are still the same thing as far as PostgreSQL is concerned but some form builders will treat them differently: varchar gets an <input type="text"> whereas text gets a multi-line <textarea>.
While the accepted answer is excellent, I wanted to add an answer here that hopefully better deals with the original posters question part 2, for non experts like myself.
How do I create a migration to replace the type of that column
generating scaffold migration
You can generate a migration to hold your change by typing in your console (just replace the table for your tables name, and column for you column name)
rails generate migration change_table_column
This will generate skeleton migration inside you Rails application /db/migrate/ folder. This migration is a placeholder for your migration code.
For example I want to create a migration to change the type of a column from string to text, in a table called TodoItems:
class ChangeTodoItemsDescription < ActiveRecord::Migration
def change
# enter code here
change_column :todo_items, :description, :text
end
end
Running your migration
Once you've entered the code to change the column just run:
rake db:migrate
To apply your migration. If you make an error you can always revert the change with:
rake db:rollack
Up and Down methods
The accepted answer references Up and Down methods, instead of the newer Change method. Since rails 3.2 old style Up and Down Methods presented a few advantages over the newer Change method. 'Up and Down' avoid ActiveRecord::IrreversibleMigration exception. Since the release of Rails 4 you can use reversible to avoid this error:
class ChangeProductsPrice < ActiveRecord::Migration
def change
reversible do |dir|
change_table :products do |t|
dir.up { t.change :price, :string }
dir.down { t.change :price, :integer }
end
end
end
end
Enjoy Rails :)