Class: PostgreSQLCursor::Cursor

Inherits:
Object
  • Object
show all
Includes:
Enumerable
Defined in:
lib/postgresql_cursor/cursor.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(sql, options = {}) ⇒ Cursor

Public: Start a new PostgreSQL cursor query sql - The SQL statement with interpolated values options - hash of processing controls

while: value    - Exits loop when block does not return this value.
until: value    - Exits loop when block returns this value.
fraction: 0.1..1.0    - The cursor_tuple_fraction (default 1.0)
block_size: 1..n      - The number of rows to fetch per db block fetch
                        Defaults to 1000
with_hold       - Allows the query to remain open across commit points.

Examples

PostgreSQLCursor::Cursor.new("select ....")

Returns the cursor object when called with new.



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# File 'lib/postgresql_cursor/cursor.rb', line 40

def initialize(sql, options={})
  @sql        = sql
  @options    = options
  @connection = @options.fetch(:connection) { ::ActiveRecord::Base.connection }
  @count      = 0
  @iterate    = options[:instances] ? :each_instance : :each_row
end

Instance Attribute Details

#connection ⇒ Object (readonly)

Returns the value of attribute connection.



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# File 'lib/postgresql_cursor/cursor.rb', line 23

def connection
  @connection
end

#count ⇒ Object (readonly)

Returns the value of attribute count.



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# File 'lib/postgresql_cursor/cursor.rb', line 23

def count
  @count
end

#options ⇒ Object (readonly)

Returns the value of attribute options.



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# File 'lib/postgresql_cursor/cursor.rb', line 23

def options
  @options
end

#result ⇒ Object (readonly)

Returns the value of attribute result.



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# File 'lib/postgresql_cursor/cursor.rb', line 23

def result
  @result
end

#sql ⇒ Object (readonly)

Returns the value of attribute sql.



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# File 'lib/postgresql_cursor/cursor.rb', line 23

def sql
  @sql
end

Instance Method Details

#cast_types(row) ⇒ Object 



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# File 'lib/postgresql_cursor/cursor.rb', line 155

def cast_types(row)
  row
end

#close ⇒ Object

Public: Closes the cursor



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# File 'lib/postgresql_cursor/cursor.rb', line 211

def close
  @connection.execute("close cursor_#{@cursor}")
end

#column_types ⇒ Object 



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# File 'lib/postgresql_cursor/cursor.rb', line 159

def column_types
  return nil if ::ActiveRecord::VERSION::MAJOR < 4
  return @column_types if @column_types

  types = {}
  fields = @result.fields
  fields.each_with_index do |fname, i|
    ftype = @result.ftype i
    fmod  = @result.fmod i
    types[fname] = @connection.get_type_map.fetch(ftype, fmod) { |oid, mod|
      warn "unknown OID: #{fname}(#{oid}) (#{sql})"
      OID::Identity.new
    }
  end

  @column_types = types
end

#each(&block) ⇒ Object

Public: Yields each row of the result set to the passed block

Yields the row to the block. The row is a hash with symbolized keys.

{colname: value, ....}

Returns the count of rows processed



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# File 'lib/postgresql_cursor/cursor.rb', line 67

def each(&block)
  if @iterate == :each_row
    self.each_row(&block)
  elsif @iterate == :each_array
    self.each_array(&block)
  else
    self.each_instance(@type, &block)
  end
end

#each_array(&block) ⇒ Object 



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# File 'lib/postgresql_cursor/cursor.rb', line 84

def each_array(&block)
  old_iterate = @iterate
  @iterate = :each_array
  begin
    rv = self.each_tuple do |row|
      block.call(row)
    end
  ensure
    @iterate = old_iterate
  end
  rv
end

#each_instance(klass = nil, &block) ⇒ Object 



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# File 'lib/postgresql_cursor/cursor.rb', line 97

def each_instance(klass=nil, &block)
  klass ||= @type
  self.each_tuple do |row|
    if ::ActiveRecord::VERSION::MAJOR < 4
      model = klass.send(:instantiate,row)
    else
      @column_types ||= column_types
      model = klass.send(:instantiate, row, @column_types)
    end
    block.call(model)
  end
end

#each_row(&block) ⇒ Object 



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# File 'lib/postgresql_cursor/cursor.rb', line 77

def each_row(&block)
  self.each_tuple do |row|
    row = row.symbolize_keys if @options[:symbolize_keys]
    block.call(row)
  end
end

#each_tuple(&block) ⇒ Object

:nodoc:



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# File 'lib/postgresql_cursor/cursor.rb', line 131

def each_tuple(&block) #:nodoc:
  has_do_until  = @options.has_key?(:until)
  has_do_while  = @options.has_key?(:while)
  @count        = 0
  @column_types = nil
  with_optional_transaction do
    begin
      open
      while (row = fetch) do
        break if row.size==0
        @count += 1
        rc = block.call(row)
        break if has_do_until && rc == @options[:until]
        break if has_do_while && rc != @options[:while]
      end
    rescue Exception => e
      raise e
    ensure
      close if @block
    end
  end
  @count
end

#fetch(options = {}) ⇒ Object

Public: Returns the next row from the cursor, or empty hash if end of results

Returns a row as a hash of ‘colname’=>value,…



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# File 'lib/postgresql_cursor/cursor.rb', line 190

def fetch(options={})
  open unless @block
  fetch_block if @block.size==0
  row = @block.shift
  row = row.symbolize_keys if row && options[:symbolize_keys]
  row
end

#fetch_block(block_size = nil) ⇒ Object

Private: Fetches the next block of rows into @block



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# File 'lib/postgresql_cursor/cursor.rb', line 199

def fetch_block(block_size=nil)
  block_size ||= @block_size ||= @options.fetch(:block_size) { 1000 }
  @result = @connection.execute("fetch #{block_size} from cursor_#{@cursor}")

  if @iterate == :each_array
    @block = @result.each_row.collect {|row| row }
  else
    @block = @result.collect {|row| row }
  end
end

#iterate_type(type = nil) ⇒ Object

Specify the type to instantiate, or reset to return a Hash



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# File 'lib/postgresql_cursor/cursor.rb', line 49

def iterate_type(type=nil)
  if type.nil? || type == Hash
    @iterate = :each_row
  elsif type == Array
    @iterate = :each_array
  else
    @iterate = :each_instance
    @type    = type
  end
  self
end

#open ⇒ Object

Public: Opens (actually, “declares”) the cursor. Call this before fetching



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# File 'lib/postgresql_cursor/cursor.rb', line 178

def open
  set_cursor_tuple_fraction
  #@cursor = Digest::MD5.hexdigest(@sql)
  @cursor = SecureRandom.uuid.gsub("-","")
  hold = @options[:with_hold] ? 'with hold ' : ''
  @result = @connection.execute("declare cursor_#{@cursor} cursor #{hold}for #{@sql}")
  @block = []
end

#pluck(*cols) ⇒ Object

Returns an array of columns plucked from the result rows. Experimental function, as this could still use too much memory and negate the purpose of this libarary. Should this return a lazy enumerator instead?



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# File 'lib/postgresql_cursor/cursor.rb', line 114

def pluck(*cols)
  options = cols.last.is_a?(Hash) ? cols.pop : {}
  @options.merge!(options)
  @options[:symbolize_keys] = true
  self.iterate_type(options[:class]) if options[:class]
  cols    = cols.map {|c| c.to_sym }
  result  = []

  self.each() do |row|
    row = row.symbolize_keys if row.is_a?(Hash)
    result << cols.map { |c| row[c] }
  end

  result.flatten! if cols.size == 1
  result
end

#set_cursor_tuple_fraction(frac = 1.0) ⇒ Object

Private: Sets the PostgreSQL cursor_tuple_fraction value = 1.0 to assume all rows will be fetched This is a value between 0.1 and 1.0 (PostgreSQL defaults to 0.1, this library defaults to 1.0) used to determine the expected fraction (percent) of result rows returned the the caller. This value determines the access path by the query planner.



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# File 'lib/postgresql_cursor/cursor.rb', line 228

def set_cursor_tuple_fraction(frac=1.0)
  @cursor_tuple_fraction ||= @options.fetch(:fraction) { 1.0 }
  return @cursor_tuple_fraction if frac == @cursor_tuple_fraction
  @cursor_tuple_fraction = frac
  @result = @connection.execute("set cursor_tuple_fraction to  #{frac}")
  frac
end

#with_optional_transaction ⇒ Object

Private: Open transaction unless with_hold option, specified



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# File 'lib/postgresql_cursor/cursor.rb', line 216

def with_optional_transaction
  if @options[:with_hold]
    yield
  else
    @connection.transaction { yield }
  end
end