I have an existing table that I'd like to use for a Rails application.
It's a simple table with only 4 columns. However it does not yet have id column. And also new data will be added periodically.
I am trying to find a way to add the id column and populate it.
I guess I have two options, but being a noob I am sure there are better ways.
Option 1: I can add the id column and populate it when I parse raw data into CSV files, and then import it to the Rails database. In this case, when I parse the data into CSV files, I need to figure out how to find the last used unique id is.
Option 2: Parse raw data into CSV files, then import to the Rails database. Then my rails application will populate the id column for the new data entries.
If Rails has a built in method or GEM that can populate the id fields for the new entries, that would be great. In that case I will go with the Option 2.
If not, I think it's easier to go with the Option 1.
So I guess the question becomes this: Can Rails automatically populate the id column of entries with blank id field?
Thanks!
Either option should work because the underlying database will automatically handle the id column since it's the primary key. So create the table using a migration, then parse, import, and add the CSV data to your database via which ever method sits best.
Related
Here is the problem:
I have Ruby on Rails project that has a table that have almost 100k rows and I have a binary column and I want to make changes in the content data on this column.
So I must iterate over those 100k rows, making changes on that row on particular column, saving it back on database.
But I must keep track of changes because these changes could fail and I should have someway to re-start data change from where I stopped.
Here is what I thought of a way of doing it:
Create a Migration to have a table MigrationTrack to track all records that have being migrated
Create a model of the above migration
Create a rake task that grabs all 100k from TableToUpdate and iterate over them, saving data back to row and save its ID on MigrationTrack. Create a logic to have a join on TableToUpdate and MigrationTrack to filter only ids that I haven't updated yet
After above migration finished create another migration to drop MigrationTrack table and remove its model.
Is there any other "Railsh way" to do that? Anyone have done such change?
Thanks
I would do it like this:
Add and deploy a migration adding a new column with the desired data type to the database table.
Add code to your model that save the value from the old column into the new column too.
Run a rake task or a simple one-liner in the console that touches all records to make sure the code introduced in step one ran on each record.
After this step, you can manually verify if all records in the database have both columns set as expected.
Switch using the new attribute instead of the old attribute in the code.
Drop the old column.
For simple cases, try running a simple view to check how it will turn out to be, for example, if your migration is
change_column :table, :boolean_field, 'integer USING CASE boolean_field THEN ...'
then you try do a simple select query with your cast, if you need more safey, you can create 'up' and 'down' methods on your migrations, then you can create a backup table on up, and on down, you can revert the values
I have existing rails app that have some tables with some data. I did the CRUD operation directly from postgresql client before using activeadmin.
I don't know whether I missed the documentation or this is a bug: activeadmin cannot detect my existing autoincrement id for table.
If I refresh the submitted form until the auto increment id surpass the existing id in my table, it works.
First think which I could think of would be that you have passed the id parameter in permit params.
Please check that and if is present then remove it.
Secondly,as mentioned in the post that there are already data in the database so there is a problem with the sequences generated, since they can be only used once.
The solution is to set the sequence for your song_artists.id column to the highest value in the table with a query like this:
SELECT setval('song_artist_id_seq', (SELECT max(id) FROM song_artists));
I am assuming that your sequence name "song_artist_id_seq", table name "song_artist", and column name "id".
To get the sequence name run the below mentioned command:
SELECT pg_get_serial_sequence('tablename', 'columname');
For Resetting the postgres sequences from rails console:
ActiveRecord::Base.connection.tables.each do |t|
ActiveRecord::Base.connection.reset_pk_sequence!(t)
end
Another solution would be to override the save() method in your song_artist class to manually set the song_artist id for new records but is not advisable.
I have a form which will be uploading a CSV file with table name. Using this table name i have to create a table in Postgresql and then i have move the data in CSV to that table.
As i understood Ruby on Rails works with model(related to a table) to write data. But when i create a table dynamically i should also create a model. But I Have searched on internet for the solution but no success.
So Can i insert the data into the temporary table without model?
Thanks in advance.
in the application i am currently creating in ruby on rails. I am trying to do some tests in rails console where i have to destroy data in the database and the database is connected to a server. I am importing an XML and parsing it and putting it into a database with scaffolding.
Now what i need: Basically what i am attempting to do is to destroy the data and replace it with a new one every week..but the problem i am getting, the userid is gone up to 700+ and there are only 50 records :S cause it doesnt reset...
To delete all records i am currently using "whatever.destroy_all" does the trick
Any help?
Btw i am using SQLITE
The ID column created in the table usually is set as unique and to increment by 1 for each new record, which is why each time you destroy and add new data the ID keeps getting higher.
The fact that the ID # is getting larger and larger is not an issue at all.
If you really want to start back at zero, I would think you could drop the table and recreate it, but that seems like overkill for a trivial issue.
Regarding the connection to the other scaffold, how are you connecting the two and what do they both represent?
Ideally the data population for testing should be done through fixtures (or easy tools such as factorygirl etc..)
The main advantage of having a fix data set is you can run your tests in any environment. But as per your requirement you can do something like this,
When you populate the date through the active records pass the id parameter as well
Ex: User.new(:id => 1, :name => "sameera").create
By this way you can have constant id's But make sure you increment the id accordingly.
What is the best way to test for an empty database in rails? I generated a model chardata and the controller, Chardatum. I want to loop through the database and extract a certain column, but I need a way to test if the database is empty first.
If you are fetching some Chardata allready you could do:
#chardata.any?
It depends on two things.
What kind of database are you using?
And by empty, do you mean the tables have not been created yet? or just that data has not been inserted yet in to the tables?
To see if the chardatas table has no rows before proceeding:
Chardata.count.zero?
Assuming you're using MySQL, you can use the following command to see if tables have been created already in your database
Chardata.count_by_sql "SELECT COUNT(DISTINCT 'table_name') FROM 'information_schema'.'columns' WHERE 'table_schema' = 'your_db_name'".zero?
You can also check if the table has been created with CharDatum.table_exists?.