Class: ActiveRecord::PostgreSQLCursor

Inherits:
Object
  • Object
show all
Includes:
Enumerable
Defined in:
lib/activerecord-postgresql-cursors.rb

Overview

PostgreSQLCursor is an Enumerable class so you can use each, map, any? and all of those nice Enumerable methods.

At the moment, cursors aren’t scrollable and are fetch forward-only and read-only.

Instance Method Summary collapse

Constructor Details

#initialize(model, cursor_name, relation, join_dependency = nil) ⇒ PostgreSQLCursor

Returns a new instance of PostgreSQLCursor.



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# File 'lib/activerecord-postgresql-cursors.rb', line 15

def initialize(model, cursor_name, relation, join_dependency = nil)
  @model = model
  @relation = relation
  @join_dependency = join_dependency

  @cursor_name = if cursor_name
    @model.connection.quote_table_name(cursor_name.gsub(/"/, '\"'))
  end

  @query = model.connection.unprepared_statement do
    relation.to_sql
  end
end

Instance Method Details

#each ⇒ Object

Calls block once for each record in the cursor, passing that record as a parameter.



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# File 'lib/activerecord-postgresql-cursors.rb', line 35

def each
  @model.transaction do
    begin
      declare_cursor
      if @join_dependency
        rows = Array.new
        last_id = nil

        while row = fetch_forward
          instantiated_row = @join_dependency.instantiate([row], @join_dependency.aliases).first

          current_id = instantiated_row[@join_dependency.join_root.primary_key]
          last_id ||= current_id
          if last_id == current_id
            rows << row
            last_id = current_id
          else
            yield @join_dependency.instantiate(rows, @join_dependency.aliases).first
            rows = [ row ]
          end
          last_id = current_id
        end

        if !rows.empty?
          yield @join_dependency.instantiate(rows, @join_dependency.aliases).first
        end
      else
        while row = fetch_forward
          yield @model.instantiate(row)
        end
      end
    ensure
      close_cursor
    end
  end
  nil
end

#inspect ⇒ Object 



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# File 'lib/activerecord-postgresql-cursors.rb', line 29

def inspect
  %{#<ActiveRecord::PostgreSQLCursor cursor_name: "#{cursor_name}", query: "#{@query}">}
end