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 50

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

Instance Attribute Details

#connection ⇒ Object (readonly)

Returns the value of attribute connection.



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# File 'lib/postgresql_cursor/cursor.rb', line 33

def connection
  @connection
end

#count ⇒ Object (readonly)

Returns the value of attribute count.



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# File 'lib/postgresql_cursor/cursor.rb', line 33

def count
  @count
end

#options ⇒ Object (readonly)

Returns the value of attribute options.



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# File 'lib/postgresql_cursor/cursor.rb', line 33

def options
  @options
end

#result ⇒ Object (readonly)

Returns the value of attribute result.



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# File 'lib/postgresql_cursor/cursor.rb', line 33

def result
  @result
end

#sql ⇒ Object (readonly)

Returns the value of attribute sql.



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# File 'lib/postgresql_cursor/cursor.rb', line 33

def sql
  @sql
end

Instance Method Details

#cast_types(row) ⇒ Object 



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

def cast_types(row)
  row
end

#close ⇒ Object

Public: Closes the cursor



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# File 'lib/postgresql_cursor/cursor.rb', line 283

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

#column_types ⇒ Object 



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# File 'lib/postgresql_cursor/cursor.rb', line 232

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 83

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

#each_array(&block) ⇒ Object 



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# File 'lib/postgresql_cursor/cursor.rb', line 100

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_array_batch(&block) ⇒ Object 



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# File 'lib/postgresql_cursor/cursor.rb', line 133

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

#each_batch(&block) ⇒ Object

:nodoc:



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# File 'lib/postgresql_cursor/cursor.rb', line 206

def each_batch(&block) #:nodoc:
  has_do_until = @options.key?(:until)
  has_do_while = @options.key?(:while)
  @count = 0
  @column_types = nil
  with_optional_transaction do
    begin
      open
      while (batch = fetch_block)
        break if batch.empty?
        @count += 1
        rc = block.call(batch)
        break if has_do_until && rc == @options[:until]
        break if has_do_while && rc != @options[:while]
      end
    ensure
      close if @block
    end
  end
  @count
end

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



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# File 'lib/postgresql_cursor/cursor.rb', line 113

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_instance_batch(klass = nil, &block) ⇒ Object 



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# File 'lib/postgresql_cursor/cursor.rb', line 146

def each_instance_batch(klass=nil, &block)
  klass ||= @type
  self.each_batch do |batch|
    models = batch.map 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
    end
    block.call(models)
  end
end

#each_row(&block) ⇒ Object 



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# File 'lib/postgresql_cursor/cursor.rb', line 93

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

#each_row_batch(&block) ⇒ Object 



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# File 'lib/postgresql_cursor/cursor.rb', line 126

def each_row_batch(&block)
  self.each_batch do |batch|
    batch.map!(&:symbolize_keys) if @options[:symbolize_keys]
    block.call(batch)
  end
end

#each_tuple(&block) ⇒ Object

:nodoc:



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# File 'lib/postgresql_cursor/cursor.rb', line 182

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 262

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 271

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_batched(batched = true) ⇒ Object 



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# File 'lib/postgresql_cursor/cursor.rb', line 72

def iterate_batched(batched=true)
  @batched = batched
  self
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 60

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 251

def open
  set_cursor_tuple_fraction
  @cursor = SecureRandom.uuid.gsub("-","")
  hold = @options[:with_hold] ? 'with hold ' : ''
  @result = @connection.execute("declare cursor_#{@cursor} no scroll 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 165

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 300

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 288

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