algebra_db

AlgebraDB

This is a database library for Ruby based on relational expressions. Most other database libraries, like the excellent sequel or activerecord are based on some idea of a scoped dataset, which is essentially an object that you can chain methods on to do further filtering, ordering, or what have you. AlgebraDB is instead based on a sort of typed query builder. Your queries return arrays of structs, custom-made for whatever query you're doing. This encourages us to use the full functionality of our database, resulting in faster and more correct queries.

An example is probably illustrative...

Example

Let's say I have two tables. One is a users table, defined like this:

CREATE TABLE users(
  id BIGINT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
  first_name TEXT NOT NULL,
  last_name TEXT NOT NULL
);

-- Probably some sort of "What did the user do" thing.
CREATE TABLE user_audits(
  id BIGINT GENERATED ALWAYS AS IDENTITY PRIAMRY KEY,
  user_id BIGINT REFERENCES users(id) NOT NULL,
  scoped_granted TEXT[] NOT NULL,
  values_changes JSONB DEFAULT '{}'::jsonb
);

Now, these two tables are relatively nice to work with. But, what if I wanted to run a query that gave me all the audit logs performed under similar scopes, and what users performed those? This is already a bit of an annoying query, but it gets worse if I want to include the users' full names as well.

With AlgebraDB, we would define some classes like this:

##
# Basic user table
class User < AlgebraDB::Table
  self.table_name = :users

  column :id, :Integer
  column :first_name, :Text
  column :last_name, :Text

end

##
# Audit log for users
class UserAudit < AlgebraDB::Table
  self.table_name = :user_audits

  column :id, :Integer
  column :user_id, :Integer
  column :scopes_granted, AlgebraDB::Value::Array::Text
  column :changes, AlgebraDB::Value::JSONB
end

We could then run a query like this:

query = AlgebraDB::Statement::Select.run_syntax do
  parent_audits = all(UserAudit)
  parent_audit_users = joins(User) do |user|
    user.id.eq(parent_audits.user_id)
  end
  child_audits = joins(UserAudit) do |other_audit|
    other_audit.scopes_granted.overlaps(parent_audits.scopes_granted).and(
      other_audits.id.neq(parent_audits.id)
    )
  end
  child_audit_users = joins(User) do |user|
    user.id.eq(child_audits.user_id)
  end
  select(
    parent_audit_id: parent_audits.id,
    parent_audit_user: parent_audit_users.first_name.append(raw_param(' ')).append(parent_audit_users.last_name),
    child_audit_id: child_audits.id,
    child_audit_user: child_audit_users.first_name.append(raw_param(' ')).append(child_audit_users.last_name)
  )
end

This, of course, is not the best code. We're doing a lot of repetition. However, since AlgebraDB operates on tables instead of records, we can define some cleanup easily:

##
# Basic user table
class User < AlgebraDB::Table
  self.table_name = :users

  column :id, :Integer
  column :first_name, :Text
  column :last_name, :Text

  ##
  # Instances are a *table in a query*, so this works!
  def full_name
    first_name.concat(AlgebraDB::Build.param(' ')).concat(last_name)
  end
end

##
# Audit log for users
class UserAudit < AlgebraDB::Table
  self.table_name = :user_audits

  column :id, :Integer
  column :user_id, :Integer
  column :scopes_granted, AlgebraDB::Value::Array::Text
  column :changes, AlgebraDB::Value::JSONB

  relationship :user, User do |user|
    user.id.eq(user_id)
  end

  relationship :similar_audits, UserAudit do |other_audit|
    other_audit.scopes_granted.overlaps(scopes_granted).and(
      other_audit.id.neq(id)
    )
  end
end

Now we only need to write:

AlgebraDB::Statement::Select.run_syntax do
  parent_audits = all(UserAudit)
  parent_audit_users = join_relationship(parent_audits.user)
  child_audits = join_relationship(parent_audits.similar_audits)
  child_audit_users = join_relationship(child_audits.user)
  select(
    parent_audit_id: parent_audits.id,
    parent_audit_user: parent_audit_users.full_name,
    child_audit_id: child_audits.id,
    child_audit_user: child_audit_users.full_name
  )
end

Notice a few things we did here that make this moderately magic:

1. We joined in the same table multiple times very, very easily. These tables have different aliases in the query, so if we wanted only child audits by a user with a name like "bob", we could have just added a where(child_audit_users.full_name.ilike(raw_param('Bob')))
2. All of the user-supplied data happens via postgres parameters. We're not putting raw SQL strings anywhere: even the space in the full_name method is parameterized!
3. We wrote an ad-hoc aliased select list, which will be converted at runtime to ruby Struct instances with the right keys. That means we can sort those records, use them as keys in a hash, or do whatever we want, easily.

In the future this will make way for powerful aggregation functionality. Postgres already has ARRAY_AGG and JSONB_AGG. Instead of making multiple queries to do eager-loading, or making one big query and then performing reassociation yourself, you'll be able to let the database (which is a hell of a lot faster than Ruby) do it for you!

Installation

Add this line to your application's Gemfile:

gem 'algebra_db'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install algebra_db

Usage

TODO: Write usage instructions here

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/algebra_db.

License

The gem is available as open source under the terms of the MIT License.