Class: BigRecord::ConnectionAdapters::View

Inherits:
Object
  • Object
show all
Defined in:
lib/big_record/connection_adapters/view.rb

Overview

Named Views

To use column-oriented databases more efficiently, it helps to know exactly which specific columns are required for a query.

For example, supposing we’re designing two queries: (A) used on the front page of a website. (B) used on the summary page for a particular item.

Since we know these two queries will be serving up different information, we can also figure out which columns are needed by each. In general, query (A) would only require a subset of columns of (B). This functionality is analogous to the SQL command "SELECT column1,column2 …" for defining specific columns to query for.

Named views are defined in models by using the BigRecord::Base.view macro like in the following example: 

  class Book < BigRecord::Base
    column :title,   :string
    column :author,             :string
    column :description,        :string
    column :links,              :string,  :collection => true

    view :front_page, :title, :author
    view :summary_page, :title, :author, :description

    # Override default if you don't want all columns returned
    view :default, :title, :author, :description
  end

Now, whenever you work with a Book record, it will only returned the columns you specify according to the view option you pass. i.e. 

  >> Book.find(:first, :view => :front_page)
  => #<Book id: "2e13f182-1085-495e-9841-fe5c84ae9992", attribute:title: "Hello Thar", attribute:author: "Greg">

  >> Book.find(:first, :view => :summary_page)
  => #<Book id: "2e13f182-1085-495e-9841-fe5c84ae9992", attribute:description: "Masterpiece!", attribute:title: "Hello Thar", attribute:author: "Greg">

  >> Book.find(:first, :view => :default)
  => #<Book id: "2e13f182-1085-495e-9841-fe5c84ae9992", attribute:description: "Masterpiece!", attribute:title: "Hello Thar", attribute:links: ["link1", "link2", "link3", "link4"], attribute:author: "Greg">

Any attributes that were not loaded in as part of the view will be lazy-loaded on request. This is very inefficient and should be avoided at all costs! It’s better to load more columns in, than to have any attributes lazy-loaded afterwards.

Note: A Bigrecord model will return all the columns within the default column family (when :view option is left blank, for example). You can override the :default name view to change this behaviour.

It’s also possible to define specific columns to load at query time. To do this, you can just pass an array of columns to the :columns option of the find method and it will return only those attributes: 

  >> Book.find(:first, :columns => [:author, :description])
  => #<Book id: "2e13f182-1085-495e-9841-fe5c84ae9992", attribute:description: "Masterpiece!", attribute:author: "Greg">

Once again, any attributes not loaded during query time will be lazy-loaded on request.

Instance Attribute Summary

Instance Method Summary

Constructor Details

- (View) initialize(name, column_names, owner)

A new instance of View 



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# File 'lib/big_record/connection_adapters/view.rb', line 69

def initialize(name, column_names, owner)
  @name = name.to_s
  @column_names = column_names ? column_names.collect{|c| c.to_s} : nil
  @owner = owner
end

Instance Attribute Details

- (Object) name (readonly)

Returns the value of attribute name 



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# File 'lib/big_record/connection_adapters/view.rb', line 67

def name
  @name
end

- (Object) owner (readonly)

Returns the value of attribute owner 



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# File 'lib/big_record/connection_adapters/view.rb', line 67

def owner
  @owner
end

Instance Method Details

- (Object) column_names

Return the name of the column objects associated with this view. By default the views ‘all’ and ‘default’ return every column. 



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# File 'lib/big_record/connection_adapters/view.rb', line 97

def column_names
  @column_names || owner.column_names
end

- (Object) columns

Return the column objects associated with this view. By default the views ‘all’ and ‘default’ return every column. 



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# File 'lib/big_record/connection_adapters/view.rb', line 76

def columns
  if @column_names
    columns = []

    # First match against fully named columns, e.g. 'attribute:name'
    @column_names.each{|cn| columns << owner.columns_hash[cn] if owner.columns_hash.has_key?(cn)}

    # Now match against aliases if the number of columns found previously do not
    # match the expected @columns_names size, i.e. there's still some missing.
    if columns.size != @column_names.size
      columns_left = @column_names - columns.map{|column| column.name}
      owner.columns_hash.each { |name,column| columns << column if columns_left.include?(column.alias) }
    end

    columns
  else
    owner.columns
  end
end