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 44

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 27

def connection
  @connection
end

#count ⇒ Object (readonly)

Returns the value of attribute count.



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# File 'lib/postgresql_cursor/cursor.rb', line 27

def count
  @count
end

#options ⇒ Object (readonly)

Returns the value of attribute options.



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# File 'lib/postgresql_cursor/cursor.rb', line 27

def options
  @options
end

#result ⇒ Object (readonly)

Returns the value of attribute result.



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# File 'lib/postgresql_cursor/cursor.rb', line 27

def result
  @result
end

#sql ⇒ Object (readonly)

Returns the value of attribute sql.



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# File 'lib/postgresql_cursor/cursor.rb', line 27

def sql
  @sql
end

Instance Method Details

#cast_types(row) ⇒ Object 



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# File 'lib/postgresql_cursor/cursor.rb', line 221

def cast_types(row)
  row
end

#close ⇒ Object

Public: Closes the cursor



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# File 'lib/postgresql_cursor/cursor.rb', line 278

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

#column_types ⇒ Object 



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# File 'lib/postgresql_cursor/cursor.rb', line 225

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)

    # From @netrusov 2023-01-18. This is the same call used in the PostgreSQL Adapter
    types[fname] = @connection.send(:get_oid_type, ftype, fmod, fname)

    # # From @simi 2023-01-18 (Works as well, used old calling method)
    # types[fname] = @connection.get_type_map.fetch(ftype)
  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 80

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

#each_array(&block) ⇒ Object 



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

def each_array(&block)
  old_iterate = @iterate
  @iterate = :each_array
  begin
    rv = 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 130

def each_array_batch(&block)
  old_iterate = @iterate
  @iterate = :each_array
  begin
    rv = 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 201

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
    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 && connection.active?
  end
  @count
end

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



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# File 'lib/postgresql_cursor/cursor.rb', line 110

def each_instance(klass = nil, &block)
  klass ||= @type
  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 143

def each_instance_batch(klass = nil, &block)
  klass ||= @type
  each_batch do |batch|
    models = batch.map do |row|
      if ::ActiveRecord::VERSION::MAJOR < 4
        klass.send(:instantiate, row)
      else
        @column_types ||= column_types
        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 90

def each_row(&block)
  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 123

def each_row_batch(&block)
  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 179

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
    open
    while (row = fetch)
      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 => e
    raise e
  ensure
    close if @block && connection.active?
  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 257

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 266

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

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

#iterate_batched(batched = true) ⇒ Object 



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# File 'lib/postgresql_cursor/cursor.rb', line 69

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.

Explicitly check for type class to prevent calling equality operator on active record relation, which will load it.



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# File 'lib/postgresql_cursor/cursor.rb', line 57

def iterate_type(type = nil)
  if type.nil? || (type.instance_of?(Class) && type == Hash)
    @iterate = :each_row
  elsif type.instance_of?(Class) && 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 246

def open
  set_cursor_tuple_fraction
  @cursor = @options[:cursor_name] || ("cursor_" + SecureRandom.uuid.delete("-"))
  hold = @options[:with_hold] ? "with hold " : ""
  @result = @connection.execute("declare #{@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 162

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

  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 295

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 283

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