Rails migration file can't access models - mysql

Question

I have an Enrollment model with a status column that is populated by a (poorly formed) seed file. Currently, all of these status values are found in the EnrollmentState column stateId (which contains negative values and is not meant to be the typical index column of a table). Here are the relevant schema tables:
db/schema.rb
create_table "enrollment_states", force: :cascade do |t|
t.integer "stateId", limit: 1, default: 0, null: false
t.string "Name", limit: 20
t.boolean "Display", limit: 1, default: false
end
create_table "enrollments", force: :cascade do |t|
t.integer "status", limit: 1, default: 0
t.integer "project_id", limit: 2, default: 0, null: false
t.integer "subjId", limit: 4, null: false
t.integer "homeId", limit: 4, null: false
t.datetime "startDate"
t.integer "RAId", limit: 4, default: 0
t.integer "eligibility_state_id", limit: 1, default: 0, null: false
t.integer "secondary", limit: 1, default: 0, null: false
t.integer "idx", limit: 4, default: 0, null: false
t.integer "enrollment_state_id", limit: 4
end
I have created the enrollment_state_id column in the Enrollment model to create an association and was hoping to populate it with the Enrollment_State id that corresponds to the status column.
I have tried to do this with the following migration:
class UpdateColumnValues < ActiveRecord::Migration
def change
Enrollment.connection.schema_cache.clear!
Enrollment.reset_column_information
Enrollment.all.each do |e|
e.update_attribute(enrollment_state_id: EnrollmentState.find_by(stateId: e.status).id)
end
end
end
However, the migration file cannot find the Enrollment data in the database! I get this error in my console after running rake db:migrate:
rake aborted!
StandardError: An error has occurred, all later migrations canceled:
Mysql2::Error: Table 'enrollment.enrollment' doesn't exist: SELECT `enrollment`.* FROM `enrollment`/Users/ben/Desktop/enrollment_app/db/migrate/20150711175101_update_column_values.rb:6:in `change'
ActiveRecord::StatementInvalid: Mysql2::Error: Table 'enrollment.enrollment' doesn't exist: SELECT `enrollment`.* FROM `enrollment`
/Users/ben/Desktop/enrollment_app/db/migrate/20150711175101_update_column_values.rb:6:in `change'
Mysql2::Error: Table 'enrollment.enrollment' doesn't exist
/Users/ben/Desktop/enrollment_app/db/migrate/20150711175101_update_column_values.rb:6:in `change'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)
Any ideas why my migration file can't access my Enrollment or EnrollmentState models? Or how to do this another way maybe?

Answer 1

Rails can find the model fine but it is looking in the wrong table for your enrollments. As you already have discovered this is due setting the table_name of your Enrollment model.
Rails is built around strong conventions, follow them and everything tends to go pretty smoothly. Break them and you end up like a drag queen in a nazi convention.
The ActiveRecord convention is that models have a singular name (User) which corresponds to a table in the plural users. Columns which end with _id are foreign keys.
Since Rails is so strongly built on convention than the first step if you have to use an existing database structure from somewhere else should be writing migrations to beat the database into conformity. Rename columns to snake_case. Make sure any columns that reference other tables have indexes and foreign keys. This avoid stupid time consuming errors because you have done ’status_id’ (which is correct) instead of statusId.
And you will be able to pass your work to other developers without feeling ashamed.