Info

Rails db adapter for Impala layer over Kudu database.

Usage

Requirements

Active connection to Impala host and port 21000.

Config database.yml

We need to config our yml like:

default: &default
  adapter: kudu
  host: 'localhost'
  port: 21000
  user: 'test'
  password: 'test'
  timeout: 5000

User and password not required.

Supported migration functionality

With our adapter almost all migration functionality is supported, such as:

create_table
remove_table
rename_table
add_column
remove_column
rename_column
and so on...

Current limitations

Creating any indexes (KUDU supports only primary key fields)

Examples

Here is some examples...

Create table

Because Kudu does not support AUTO INCREMENT INT fields we must ensure any primary key field is created as string field.

class CreateUsers < ActiveRecord::Migration[5.1]
  def change
    create_table :users, id: false do |t|
      t.string :id, primary_key: true
      t.string :account_id, null: false
      t.string :name, null: false
      t.string :email, null: false
      t.string :company_id, null: false
      t.string :company_name
      t.timestamps
    end
  end
end

In example above we have only 1 primary key field and our model will work fully functionally when we using update(), delete() methods.

We can set additional primary key field, like

create_table :users, id: false do |t|
      t.string :id, primary_key: true
      t.string :account_id, primary_key: true

Here, we have two fields in primary key (id, account_id) and with KUDU table will be created with those 2 primary keys, but due to limitation of Rails will not be possible to use model delete(), update() methods.

Add new column

Basic case:

class AddZipCodeToUsers < ActiveRecord::Migration[5.1]
  def change
    add_column :users, :zip_code, :string
  end
end

In case of adding new primary key field, like:

class AddCompanyToUsers < ActiveRecord::Migration[5.1]
  def up
    add_column :users, :company_id, :string, primary_key: true
    reload_table_data :users, :company_id, default: '#company-id'
  end
  def down
    remove_column :users, :company_id
  end
end

we will initialize specialized method at migration side, and basically this will happen:

New table "table_name_redefined" will be created based on original table name (ex. users -> users_redefined) with included new field, new primary key field.
Old table "users" will be renamed to "users_temp"
Data will be copied from users_temp => users with additional new field and default value
Old temporary table "users_temp" will be deleted

Delete column

Basic case:

class RemoveZipCodeFromUsers < ActiveRecord::Migration[5.1]
  def change
    remove_column :users, :zip_code
  end
end

In case of deleting primary key field (existing) procedure is same like for adding new column with primary key.

Model associations

Model associations will work without foreign keys, like:

class CreateAccounts < ActiveRecord::Migration[5.1]
  def change
    create_table :accounts, id: false do |t|
      t.string :id, primary_key: true
      t.boolean :is_active, default: true
      t.timestamps
    end
  end
end

class Account < ApplicationRecord
  has_many :users, foreign_key: 'account_id'
end

and table Users with following construct...

class CreateUsers < ActiveRecord::Migration[5.1]
  def change
    create_table :users, id: false do |t|
      t.string :id, primary_key: true
      t.string :account_id, null: false
      t.string :name, null: false
      t.string :email, null: false
      t.string :company_id, null: false
      t.string :company_name
      t.timestamps
    end
  end
end

class User < ApplicationRecord
  belongs_to :account, primary_key: 'id'
end

This way we're able to do

Account.first.users => [#User, #User, ...]

User.first.account => #Account

kudu_adapter

Development

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