Class: AWS::SimpleDB::ItemCollection

Inherits:
Object
  • Object
show all
Includes:
Core::Collection::WithLimitAndNextToken
Defined in:
lib/aws/simple_db/item_collection.rb

Overview

Represents a collection of items in a SimpleDB domain.

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from Core::Collection

#enum, #first, #in_groups_of, #page

Constructor Details

#initialize(domain, options = {}) ⇒ ItemCollection

Parameters:

  • domain (Domain) —

    The domain that you want an item collection for.



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# File 'lib/aws/simple_db/item_collection.rb', line 49

def initialize domain, options = {}
  @domain = domain
  @output_list = options[:output_list] || 'itemName()'
  @conditions = options[:conditions] || []
  @sort_instructions = options[:sort_instructions]
  @not_null_attribute = options[:not_null_attribute]
  @limit = options[:limit]
  super
end

Instance Attribute Details

#domain ⇒ Domain (readonly)

Returns The domain the items belong to.

Returns:

  • (Domain) —

    The domain the items belong to.



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# File 'lib/aws/simple_db/item_collection.rb', line 36

def domain
  @domain
end

Instance Method Details

#[](item_name) ⇒ Item

Note:

This does not make a request to SimpleDB.

Retuns an item with the given name.

You can ask for any item. The named item may or may not actually exist in SimpleDB.

Examples:

Get an item by symbol or string name


item = domain.items[:itemname]
item = domain.items['itemname']

Parameters:

  • item_name (String, Symbol) —

    name of the item to get.

Returns:

  • (Item) —

    Returns an item with the given name.



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# File 'lib/aws/simple_db/item_collection.rb', line 91

def [] item_name
  Item.new(domain, item_name.to_s)
end

#count(options = {}, &block) ⇒ Integer Also known as: size

Counts the items in the collection.

domain.items.count

You can specify what items to count with #where:

domain.items.where(:color => "red").count

You can also limit the number of items to count:

# count up to 500 items and then stop
domain.items.limit(500).count

Parameters:

  • options (Hash) (defaults to: {}) —

    Options for counting items.

Options Hash (options):

  • :consistent_read (Boolean) — default: false —

    Causes this method to yield the most current data in the domain when true.

  • :where (Object) —

    Restricts the item collection using #where before querying.

  • :limit (Integer) —

    The maximum number of items to count in SimpleDB.

Returns:

  • (Integer) —

    The number of items counted.



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# File 'lib/aws/simple_db/item_collection.rb', line 205

def count options = {}, &block

  handle_query_options(options) do |collection, opts|
    return collection.count(opts, &block)
  end

  options = options.merge(:output_list => "count(*)")

  count = 0
  next_token = nil

  begin

    response = select_request(options, next_token)

    if 
      domain_item = response.items.first and
      count_attribute = domain_item.attributes.first
    then
      count += count_attribute.value.to_i
    end

    break unless next_token = response[:next_token]

  end while limit.nil? || count < limit

  count

end

#create(item_name, attributes) ⇒ Item

Creates a new item in SimpleDB with the given attributes: 

domain.items.create('shirt', {
  'colors' => ['red', 'blue'],  
  'category' => 'clearance'})

Returns a reference to the object that was created.

Parameters:

  • item_name (String) —

    The name of the item as you want it stored in SimpleDB.

  • attributes (Hash) —

    A hash of attribute names and values you want to store in SimpleDB.

Returns:

  • (Item) —

    Returns a reference to the object that was created.



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# File 'lib/aws/simple_db/item_collection.rb', line 71

def create item_name, *args
  item = self[item_name]
  item.attributes.replace(*args)
  item
end

#each(options = {}) {|item| ... } ⇒ String?

Yields to the block once for each item in the collection. This method can yield two type of objects:

  • AWS::SimpleDB::Item objects (only the item name is populated)

  • AWS::SimpleDB::ItemData objects (some or all attributes populated)

The default mode of an ItemCollection is to yield Item objects with no populated attributes.

# only receives item names from SimpleDB
domain.items.each do |item|
  puts item.name
  puts item.class.name # => AWS::SimpleDB::Item
end

You can switch a collection into yielded AWS::SimpleDB::ItemData objects by specifying what attributes to request:

domain.items.select(:all).each do |item_data|
  puts item_data.class.name # => AWS::SimpleDB::ItemData
  puts item_data.attributes # => { 'attr-name' => 'attr-value', ... }
end

You can also pass the standard scope options to #each as well:

# output the item names of the 10 most expesive items
domain.items.each(:order => [:price, :desc], :limit => 10).each do |item|
  puts item.name
end

Parameters:

  • options (Hash) (defaults to: {})

Options Hash (options):

  • :consistent_read (Boolean) — default: false —

    Causes this method to yield the most current data in the domain.

  • :select (Mixed) —

    If select is provided, then each will yield AWS::SimpleDB::ItemData objects instead of empty AWS::SimpleDB::Item. The :select option may be:

    • :all - Specifies that all attributes should requested.

    • A single or array of attribute names (as strings or symbols). This causes the named attribute(s) to be requested.

  • :where (Object) —

    Restricts the item collection using #where before querying (see #where).

  • :order (Object) —

    Changes the order in which the items will be yielded (see #order).

  • :limit (Integer) —

    The maximum number of items to fetch from SimpleDB.

  • :batch_size (Object) —

    Specifies a maximum number of records to fetch from SimpleDB in a single request. SimpleDB may return fewer items than :batch_size per request, but never more. Generally you should not need to specify this option.

Yields:

  • (item) —

    Yields once for every item in the #domain.

Yield Parameters:

  • item (Item, ItemData) —

    If the item collection has been scoped by chaining #select or by passing the :select option then AWS::SimpleDB::ItemData objects (that contain a hash of attrbiutes) are yielded. If no list of attributes has been provided, then# AWS::SimpleDB::Item objects (with no populated data) are yielded.

Returns:

  • (String, nil) —

    Returns a next token that can be used with the exact same SimpleDB select expression to get more results. A next token is returned ONLY if there was a limit on the expression, otherwise all items will be enumerated and nil is returned.



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# File 'lib/aws/simple_db/item_collection.rb', line 167

def each options = {}, &block
  super
end

#limit ⇒ Integer #limit(value) ⇒ ItemCollection Also known as: _limit

Limits the number of items that are returned or yielded. For example, to get the 100 most popular item names:

domain.items.
  order(:popularity, :desc).
  limit(100).
  map(&:name)

Overloads:

  • #limit ⇒ Integer

    Returns the current limit for the collection.

    Returns:

    • (Integer) —

      Returns the current limit for the collection.

  • #limit(value) ⇒ ItemCollection

    Returns a collection with the given limit.

    Returns:



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# File 'lib/aws/simple_db/item_collection.rb', line 446

def limit *args
  return @limit if args.empty?
  collection_with(:limit => Integer(args.first))
end

#order(attribute, order = nil) ⇒ ItemCollection

Changes the order in which results are returned or yielded. For example, to get item names in descending order of popularity, you can do:

domain.items.order(:popularity, :desc).map(&:name)

Parameters:

  • attribute (String or Symbol) —

    The attribute name to order by.

  • order (String or Symbol) (defaults to: nil) —

    The desired order, which may be:

    • asc or ascending (the default)

    • desc or descending

Returns:

  • (ItemCollection) —

    Returns a new item collection with the given ordering logic.



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# File 'lib/aws/simple_db/item_collection.rb', line 424

def order(attribute, order = nil)
  sort = coerce_attribute(attribute)
  sort += " DESC" if order.to_s =~ /^desc(ending)?$/
  sort += " ASC" if order.to_s =~ /^asc(ending)?$/
  collection_with(:sort_instructions => sort,
                  :not_null_attribute => attribute.to_s)
end

#select(*attributes, &block) ⇒ ItemCollection

Specifies a list of attributes select from SimpleDB.

domain.items.select('size', 'color').each do |item_data|
  puts item_data.attributes # => { 'size' => ..., :color => ... }
end

You can select all attributes by passing :all or ‘*’:

domain.items.select('*').each {|item_data| ... }

domain.items.select(:all).each {|item_data| ... }

Calling #select causes #each to yield AWS::SimpleDB::ItemData objects with #attribute hashes, instead of AWS::SimpleDB::Item objects with an item name.

Parameters:

  • attributes (Symbol, String, or Array) —

    The attributes to retrieve. This can be:

    • :all or ‘*’ to request all attributes for each item

    • A list or array of attribute names as strinsg or symbols

      Attribute names may contain any characters that are valid in a SimpleDB attribute name; this method will handle escaping them for inclusion in the query. Note that you cannot use this method to select the number of items; use #count instead.

Returns:

  • (ItemCollection) —

    Returns a new item collection with the specified list of attributes to select.



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# File 'lib/aws/simple_db/item_collection.rb', line 282

def select *attributes, &block

  # Before select was morphed into a chainable method, it accepted
  # a hash of options (e.g. :where, :order, :limit) that no longer
  # make sense, but to maintain backwards compatability we still
  # consume those.
  #
  # TODO : it would be a good idea to add a deprecation warning for
  #        passing options to #select
  #
  handle_query_options(*attributes) do |collection, *args|
    return collection.select(*args, &block)
  end

  options = attributes.last.is_a?(Hash) ? attributes.pop : {}

  output_list = case attributes.flatten
  when []     then '*'
  when ['*']  then '*'
  when [:all] then '*'
  else attributes.flatten.map{|attr| coerce_attribute(attr) }.join(', ')
  end

  collection = collection_with(:output_list => output_list)

  if block_given?
    # previously select accepted a block and it would enumerate items
    # this is for backwards compatability
    collection.each(options, &block)
    nil
  else
    collection
  end

end

#where(conditions, *substitutions) ⇒ ItemCollection

Returns an item collection defined by the given conditions in addition to any conditions defined on this collection. For example:

items = domain.items.where(:color => 'blue').
  where('engine_type is not null')

# does SELECT itemName() FROM `mydomain`
#      WHERE color = "blue" AND engine_type is not null
items.each { |i| ... }

Hash Conditions

When conditions is a hash, each entry produces a condition on the attribute named in the hash key. For example:

# produces "WHERE `foo` = 'bar'"
domain.items.where(:foo => 'bar')

You can pass an array value to use an “IN” operator instead of “=”:

# produces "WHERE `foo` IN ('bar', 'baz')"
domain.items.where(:foo => ['bar', 'baz'])

You can also pass a range value to use a “BETWEEN” operator:

# produces "WHERE `foo` BETWEEN 'bar' AND 'baz'
domain.items.where(:foo => 'bar'..'baz')

# produces "WHERE (`foo` >= 'bar' AND `foo` < 'baz')"
domain.items.where(:foo => 'bar'...'baz')

Placeholders

If conditions is a string and “?” appears outside of any quoted part of the expression, placeholers is expected to contain a value for each of the “?” characters in the expression. For example:

# produces "WHERE foo like 'fred''s % value'"
domain.items.where("foo like ?", "fred's % value")

Array values are surrounded with parentheses when they are substituted for a placeholder:

# produces "WHERE foo in ('1', '2')"
domain.items.where("foo in ?", [1, 2])

Note that no substitutions are made within a quoted region of the query:

# produces "WHERE `foo?` = 'red'"
domain.items.where("`foo?` = ?", "red")

# produces "WHERE foo = 'fuzz?' AND bar = 'zap'"
domain.items.where("foo = 'fuzz?' AND bar = ?", "zap")

Also note that no attempt is made to correct for syntax:

# produces "WHERE 'foo' = 'bar'", which is invalid
domain.items.where("? = 'bar'", "foo")

Returns:

  • (ItemCollection) —

    Returns a new item collection with the additional conditions.



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# File 'lib/aws/simple_db/item_collection.rb', line 384

def where conditions, *substitutions
  case conditions
  when String
    conditions = [replace_placeholders(conditions, *substitutions)]
  when Hash
    conditions = conditions.map do |name, value|
      name = coerce_attribute(name)
      case value
      when Array
        "#{name} IN " + coerce_substitution(value)
      when Range
        if value.exclude_end?
          "(#{name} >= #{coerce_substitution(value.begin)} AND " +
            "#{name} < #{coerce_substitution(value.end)})"
        else
          "#{name} BETWEEN #{coerce_substitution(value.begin)} AND " +
            coerce_substitution(value.end)
        end
      else
        "#{name} = " + coerce_substitution(value)
      end
    end
  end

  collection_with(:conditions => self.conditions + conditions)
end