Expressions

Expressions evaluate into useful objects via a query builder like interface.

Expressions provides an API for expression types. You can build your own Expression, or use expressions created via the gems below:

# Via method definition:
def method(my_var: MyType); end

# Via type() helper:
my_var = type MyType | fetch_my_object(id: 123)

my_var is now type checked to be of type MyType when assigned to.

ℹ️ Requires: LowType

def method(my_var: Dependency); end

my_var is now automatically assigned to via dependency injection.

ℹ️ Requires: LowType and Providers

The table expression inverts the usual database query logic. Instead of building a query of what we want from the database, we build the table we want and let the expression build the query.

class PostsData < LowData
  def all
    Table[:username, :title, :body]
  end
end

This expression joins the posts table with the users table without any joins from the user's perspective.

class PostsData < LowData
  def all
    Users[:username] + Posts[:title, :body]
  end
end

The above expression generates SQL to join the user table with the posts table and results in a list of posts with the user's username included in each row.

ℹ️ Requires: LowData

Inherit from Expressions::Expression and define a hook/callback:

Gems using Expressions will do this step for you, but if you'd like to build your own expression then add gem 'expressions' to your Gemfile and run:

bundle install