Rails Arel Complex Multi Join Query

gistfile1.txt

  def self.get_docs(some_input, required_docs, optional_docs, base_id = nil)
    base_req = self.get_parameters_from_request(some_input)
    user_department_id = some_input.user_department.try("id") || -1

    doc = Document.arel_table
    dept = Department.arel_table
    dept_rule = DepartmentRule.arel_table
    dept_code = DepartmentRuleCode.arel_table
    debt_state = DepartmentRuleState.arel_table

    scope :base_scope, -> { 
      joins(:rules,:codes, :states, :documents)
      .includes(:line_of_business)
      .where(doc[:parent_document_id].eq(nil)
         .or(doc[:parent_document_id].eq(doc[:id])))
      .where(doc[:deparment_id].eq(some_input.managing_department.id))
      .where(dept_rule[:user_department_id].eq(nil)
        .or(dept_rule[:user_department_id].eq(some_input.department &&
          some_input.department.id)))
      .where(doc[:user_id].eq(nil)
        .or(doc[:user_department_id].eq(some_input.department &&
          some_input.department.id)))
      .where(lob[:code].in(doc[:line_of_businesses])
        .or(dept_rule[:line_of_business_id].eq(nil)))
      .where(dept_code[:classcode].in(doc[:class_code])
         .or(dept_code[:classcode].eq(nil)))
      .where(dept_state[:state].in(doc[:state])
         .or(dept_state[:state].eq(nil)))
      .where(dept_rule[:effective_date].lteq(some_input.effective_date)
        .or(dept_rule[:effective_date].eq(nil)))
      .where(dept_rule[:expiration_date].gteq(some_input.effective_date)
         .or(dept_rule[:expiration_date].eq(nil))) }

    if base_id
      Base = Base.find(base_id)
      if Base 
        if Base.is_a? DepartmentBase
          scope :base_condition, -> {
            where(dept_rule[:base_id].eq(base_id))
            .where(dept_rule[:user_department_id].eq(nil)
               .or(dept_rule[:user_department_id].eq(department_id))) }
        else
          scope :base_condition, -> {
            where(dept_rule[:base_id].eq(base_id)
              .or(dept_rule[:optional_for_all_departments].eq(1)))
            .where(dept_rule[:user_department_id].eq(nil)
               .or(debt_rule[:user_department_id].eq(department_id))) }
        end
      end
    else
      scope :base_condition, -> { 
        where(dept_rule[:base_id].eq(nil))
        .where(debt_rule[:optional_for_all_departments].eq(0)) }
    end

    results = self.base_scope.base_condition.uniq.order(:sequence)

  end

another option for multiple joins:
Document.joins(:departments => [:rules, :codes, :states])

where departments has association with document, but :rules, :codes, and :states are have association with department and not document.
Produces the following:
SELECT documents.* FROM documents INNER JOIN departments ON departments.document_id = documents.id INNER JOIN rules ON rules.department_id = departments.id INNER JOIN codes ON codes.department_id = departments.id INNER JOIN states ON states.department_id = department.id