de405480b5
rstring now has an autocast() function that returns the automatic casting for that value. The casting is cached so is really performed only once, at most, during the lifetime of the object.
541 lines
19 KiB
Python
541 lines
19 KiB
Python
# -*- coding: utf-8 -*-
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# Relational
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# Copyright (C) 2008 Salvo "LtWorf" Tomaselli
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#
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# Relational is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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#
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# author Salvo "LtWorf" Tomaselli <tiposchi@tiscali.it>
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#
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# This module provides a classes to represent relations and to perform
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# relational operations on them.
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import csv
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from relational.rtypes import *
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class relation (object):
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'''This objects defines a relation (as a group of consistent tuples) and operations
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A relation can be represented using a table
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Calling an operation and providing a non relation parameter when it is expected will
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result in a None value'''
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__hash__ = None
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def __init__(self, filename=""):
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'''Creates a relation, accepts a filename and then it will load the relation from
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that file. If no parameter is supplied an empty relation is created. Empty
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relations are used in internal operations.
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By default the file will be handled like a comma separated as described in
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RFC4180.'''
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self._readonly = False
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if len(filename) == 0: # Empty relation
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self.content = set()
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self.header = header([])
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return
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# Opening file
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fp = open(filename)
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reader = csv.reader(fp) # Creating a csv reader
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self.header = header(next(reader)) # read 1st line
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self.content = set()
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for i in reader: # Iterating rows
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self.content.add(tuple(map (rstring, i)))
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# Closing file
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fp.close()
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def _make_writable(self):
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'''If this relation is marked as readonly, this
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method will copy the content to make it writable too'''
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if self._readonly:
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self.content = set(self.content)
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self._readonly = False
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def save(self, filename):
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'''Saves the relation in a file. By default will save using the csv
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format as defined in RFC4180, but setting comma_separated to False,
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it will use the old format with space separated values.
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'''
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fp = open(filename, 'w') # Opening file in write mode
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writer = csv.writer(fp) # Creating csv writer
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# It wants an iterable containing iterables
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head = (self.header.attributes,)
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writer.writerows(head)
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# Writing content, already in the correct format
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writer.writerows(self.content)
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fp.close() # Closing file
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def _rearrange_(self, other):
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'''If two relations share the same attributes in a different order, this method
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will use projection to make them have the same attributes' order.
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It is not exactely related to relational algebra. Just a method used
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internally.
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Will return None if they don't share the same attributes'''
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if (self.__class__ != other.__class__):
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raise Exception('Expected an instance of the same class')
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if self.header.sharedAttributes(other.header) == len(self.header.attributes):
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return other.projection(list(self.header.attributes))
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raise Exception('Relations differ: [%s] [%s]' % (
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','.join(self.header.attributes) , ','.join(other.header.attributes)
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))
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def selection(self, expr):
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'''Selection, expr must be a valid boolean expression, can contain field names,
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constant, math operations and boolean ones.'''
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attributes = {}
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newt = relation()
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newt.header = header(list(self.header.attributes))
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for i in self.content:
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# Fills the attributes dictionary with the values of the tuple
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for j in range(len(self.header.attributes)):
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attributes[self.header.attributes[j]] = i[j].autocast()
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try:
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if eval(expr, attributes):
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newt.content.add(i)
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except Exception as e:
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raise Exception(
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"Failed to evaluate %s\n%s" % (expr, e.__str__()))
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return newt
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def product(self, other):
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'''Cartesian product, attributes must be different to avoid collisions
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Doing this operation on relations with colliding attributes will
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cause an exception.
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It is possible to use rename on attributes and then use the product'''
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if (self.__class__ != other.__class__)or(self.header.sharedAttributes(other.header) != 0):
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raise Exception(
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'Unable to perform product on relations with colliding attributes')
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newt = relation()
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newt.header = header(self.header.attributes + other.header.attributes)
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for i in self.content:
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for j in other.content:
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newt.content.add(i + j)
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return newt
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def projection(self, * attributes):
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'''Projection operator, takes many parameters, for each field to use.
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Can also use a single parameter with a list.
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Will delete duplicate items
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If an empty list or no parameters are provided, returns None'''
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# Parameters are supplied in a list, instead with multiple parameters
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if isinstance(attributes[0], list):
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attributes = attributes[0]
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# Avoiding duplicated attributes
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attributes1 = []
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for i in attributes:
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if i not in attributes1:
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attributes1.append(i)
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attributes = attributes1
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ids = self.header.getAttributesId(attributes)
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if len(ids) == 0 or len(ids) != len(attributes):
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raise Exception('Invalid attributes for projection')
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newt = relation()
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# Create the header
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h = []
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for i in ids:
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h.append(self.header.attributes[i])
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newt.header = header(h)
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# Create the body
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for i in self.content:
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row = []
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for j in ids:
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row.append(i[j])
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newt.content.add(tuple(row))
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return newt
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def rename(self, params):
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'''Operation rename. Takes a dictionary
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Will replace the itmem with its content.
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For example if you want to rename a to b, provide {"a":"b"}
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'''
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result = []
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newt = relation()
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newt.header = header(list(self.header.attributes))
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for old, new in params.items():
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newt.header.rename(old, new)
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newt.content = self.content
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newt._readonly = True
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self._readonly = True
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return newt
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def intersection(self, other):
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'''Intersection operation. The result will contain items present in both
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operands.
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Will return an empty one if there are no common items.
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Will return None if headers are different.
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It is possible to use projection and rename to make headers match.'''
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other = self._rearrange_(other) # Rearranges attributes' order
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newt = relation()
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newt.header = header(list(self.header.attributes))
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newt.content = self.content.intersection(other.content)
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return newt
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def difference(self, other):
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'''Difference operation. The result will contain items present in first
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operand but not in second one.
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Will return an empty one if the second is a superset of first.
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Will return None if headers are different.
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It is possible to use projection and rename to make headers match.'''
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other = self._rearrange_(other) # Rearranges attributes' order
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newt = relation()
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newt.header = header(list(self.header.attributes))
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newt.content = self.content.difference(other.content)
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return newt
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def division(self, other):
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'''Division operator
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The division is a binary operation that is written as R ÷ S. The
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result consists of the restrictions of tuples in R to the
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attribute names unique to R, i.e., in the header of R but not in the
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header of S, for which it holds that all their combinations with tuples
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in S are present in R.
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'''
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# d_headers are the headers from self that aren't also headers in other
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d_headers = list(
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set(self.header.attributes) - set(other.header.attributes))
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'''
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Wikipedia defines the division as follows:
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a1,....,an are the d_headers
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T := πa1,...,an(R) × S
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U := T - R
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V := πa1,...,an(U)
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W := πa1,...,an(R) - V
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W is the result that we want
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'''
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t = self.projection(d_headers).product(other)
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return self.projection(d_headers).difference(t.difference(self).projection(d_headers))
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def union(self, other):
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'''Union operation. The result will contain items present in first
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and second operands.
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Will return an empty one if both are empty.
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Will not insert tuplicated items.
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Will return None if headers are different.
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It is possible to use projection and rename to make headers match.'''
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other = self._rearrange_(other) # Rearranges attributes' order
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newt = relation()
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newt.header = header(list(self.header.attributes))
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newt.content = self.content.union(other.content)
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return newt
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def thetajoin(self, other, expr):
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'''Defined as product and then selection with the given expression.'''
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return self.product(other).selection(expr)
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def outer(self, other):
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'''Does a left and a right outer join and returns their union.'''
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a = self.outer_right(other)
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b = self.outer_left(other)
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return a.union(b)
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def outer_right(self, other):
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'''Outer right join. Considers self as left and param as right. If the
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tuple has no corrispondence, empy attributes are filled with a "---"
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string. This is due to the fact that empty string or a space would cause
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problems when saving the relation.
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Just like natural join, it works considering shared attributes.'''
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return other.outer_left(self)
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def outer_left(self, other, swap=False):
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'''Outer left join. Considers self as left and param as right. If the
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tuple has no corrispondence, empty attributes are filled with a "---"
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string. This is due to the fact that empty string or a space would cause
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problems when saving the relation.
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Just like natural join, it works considering shared attributes.'''
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||
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shared = []
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for i in self.header.attributes:
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if i in other.header.attributes:
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shared.append(i)
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newt = relation() # Creates the new relation
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# Adds all the attributes of the 1st relation
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newt.header = header(list(self.header.attributes))
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# Adds all the attributes of the 2nd, when non shared
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for i in other.header.attributes:
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if i not in shared:
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newt.header.attributes.append(i)
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# Shared ids of self
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sid = self.header.getAttributesId(shared)
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# Shared ids of the other relation
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oid = other.header.getAttributesId(shared)
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# Non shared ids of the other relation
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noid = []
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for i in range(len(other.header.attributes)):
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if i not in oid:
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noid.append(i)
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for i in self.content:
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# Tuple partecipated to the join?
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added = False
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for j in other.content:
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match = True
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for k in range(len(sid)):
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match = match and (i[sid[k]] == j[oid[k]])
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if match:
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item = list(i)
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for l in noid:
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item.append(j[l])
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newt.content.add(tuple(item))
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added = True
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# If it didn't partecipate, adds it
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if not added:
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item = list(i)
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for l in range(len(noid)):
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item.append("---")
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newt.content.add(tuple(item))
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return newt
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def join(self, other):
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||
'''Natural join, joins on shared attributes (one or more). If there are no
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shared attributes, it will behave as cartesian product.'''
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||
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# List of attributes in common between the relations
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shared = list(set(self.header.attributes)
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.intersection(set(other.header.attributes)))
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newt = relation() # Creates the new relation
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||
|
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# Adding to the headers all the fields, done like that because order is
|
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# needed
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||
newt.header = header(list(self.header.attributes))
|
||
for i in other.header.attributes:
|
||
if i not in shared:
|
||
newt.header.attributes.append(i)
|
||
|
||
# Shared ids of self
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||
sid = self.header.getAttributesId(shared)
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||
# Shared ids of the other relation
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oid = other.header.getAttributesId(shared)
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||
|
||
# Non shared ids of the other relation
|
||
noid = []
|
||
for i in range(len(other.header.attributes)):
|
||
if i not in oid:
|
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noid.append(i)
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||
|
||
for i in self.content:
|
||
for j in other.content:
|
||
match = True
|
||
for k in range(len(sid)):
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||
match = match and (i[sid[k]] == j[oid[k]])
|
||
|
||
if match:
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||
item = list(i)
|
||
for l in noid:
|
||
item.append(j[l])
|
||
|
||
newt.content.add(tuple(item))
|
||
|
||
return newt
|
||
|
||
def __eq__(self, other):
|
||
'''Returns true if the relations are the same, ignoring order of items.
|
||
This operation is rather heavy, since it requires sorting and comparing.'''
|
||
if self.__class__ != other.__class__:
|
||
return False
|
||
|
||
if set(self.header.attributes) != set(other.header.attributes):
|
||
return False
|
||
|
||
# Rearranges attributes' order so can compare tuples directly
|
||
other = self._rearrange_(other)
|
||
|
||
# comparing content
|
||
return self.content == other.content
|
||
|
||
def __str__(self):
|
||
'''Returns a string representation of the relation, can be printed with
|
||
monospaced fonts'''
|
||
m_len = [] # Maximum lenght string
|
||
for f in self.header.attributes:
|
||
m_len.append(len(f))
|
||
|
||
for f in self.content:
|
||
col = 0
|
||
for i in f:
|
||
if len(i) > m_len[col]:
|
||
m_len[col] = len(i)
|
||
col += 1
|
||
|
||
res = ""
|
||
for f in range(len(self.header.attributes)):
|
||
res += "%s" % (self.header.attributes[f].ljust(2 + m_len[f]))
|
||
|
||
for r in self.content:
|
||
col = 0
|
||
res += "\n"
|
||
for i in r:
|
||
res += "%s" % (i.ljust(2 + m_len[col]))
|
||
col += 1
|
||
|
||
return res
|
||
|
||
def update(self, expr, dic):
|
||
'''Update, expr must be a valid boolean expression, can contain field names,
|
||
constant, math operations and boolean ones.
|
||
This operation will change the relation itself instead of generating a new one,
|
||
updating all the tuples that make expr true.
|
||
Dic must be a dictionary that has the form field name:value. Every kind of value
|
||
will be converted into a string.
|
||
Returns the number of affected rows.'''
|
||
self._make_writable()
|
||
affected = 0
|
||
attributes = {}
|
||
keys = dic.keys() # List of headers to modify
|
||
f_ids = self.header.getAttributesId(
|
||
keys) # List of indexes corresponding to keys
|
||
|
||
# new_content=[] #New content of the relation
|
||
for i in self.content:
|
||
for j in range(len(self.header.attributes)):
|
||
attributes[self.header.attributes[j]] = i[j].autocast()
|
||
|
||
if eval(expr, attributes): # If expr is true, changing the tuple
|
||
affected += 1
|
||
new_tuple = list(i)
|
||
# Deleting the tuple, instead of changing it, so other
|
||
# relations can still point to the same list without
|
||
# being affected.
|
||
self.content.remove(i)
|
||
for k in range(len(keys)):
|
||
new_tuple[f_ids[k]] = rstring(dic[keys[k]])
|
||
self.content.add(tuple(new_tuple))
|
||
return affected
|
||
|
||
def insert(self, values):
|
||
'''Inserts a tuple in the relation.
|
||
This function will not insert duplicate tuples.
|
||
All the values will be converted in string.
|
||
Will return the number of inserted rows.'''
|
||
|
||
if len(self.header.attributes) != len(values):
|
||
raise Exception(
|
||
'Tuple has the wrong size. Expected %d, got %d' % (
|
||
len(self.header.attributes),
|
||
len(values)
|
||
)
|
||
)
|
||
|
||
self._make_writable()
|
||
|
||
prevlen = len(self.content)
|
||
self.content.add(tuple(map(rstring, values)))
|
||
return len(self.content) - prevlen
|
||
|
||
def delete(self, expr):
|
||
'''Delete, expr must be a valid boolean expression, can contain field names,
|
||
constant, math operations and boolean ones.
|
||
This operation will change the relation itself instead of generating a new one,
|
||
deleting all the tuples that make expr true.
|
||
Returns the number of affected rows.'''
|
||
|
||
#Not necessary self._make_writable()
|
||
|
||
l = len(self.content)
|
||
self._readonly = False
|
||
self.content = self.difference(self.selection(expr)).content
|
||
return len(self.content) - l
|
||
|
||
|
||
class header (object):
|
||
|
||
'''This class defines the header of a relation.
|
||
It is used within relations to know if requested operations are accepted'''
|
||
|
||
# Since relations are mutalbe we explicitly block hashing them
|
||
__hash__ = None
|
||
|
||
def __init__(self, attributes):
|
||
'''Accepts a list with attributes' names. Names MUST be unique'''
|
||
self.attributes = attributes
|
||
|
||
for i in attributes:
|
||
if not is_valid_relation_name(i):
|
||
raise Exception('"%s" is not a valid attribute name' % i)
|
||
|
||
if len(attributes) != len(set(attributes)):
|
||
raise Exception('Attribute names must be unique')
|
||
|
||
def __repr__(self):
|
||
return "header(%s)" % (self.attributes.__repr__())
|
||
|
||
def rename(self, old, new):
|
||
'''Renames a field. Doesn't check if it is a duplicate.
|
||
Returns True'''
|
||
|
||
if not is_valid_relation_name(new):
|
||
raise Exception('%s is not a valid attribute name' % new)
|
||
|
||
try:
|
||
id_ = self.attributes.index(old)
|
||
self.attributes[id_] = new
|
||
except:
|
||
raise Exception('Field not found: %s' & old)
|
||
return True
|
||
|
||
def sharedAttributes(self, other):
|
||
'''Returns how many attributes this header has in common with a given one'''
|
||
return len(set(self.attributes).intersection(set(other.attributes)))
|
||
|
||
def __str__(self):
|
||
'''Returns String representation of the field's list'''
|
||
return self.attributes.__str__()
|
||
|
||
def __eq__(self, other):
|
||
return self.attributes == other.attributes
|
||
|
||
def __ne__(self, other):
|
||
return self.attributes != other.attributes
|
||
|
||
def getAttributesId(self, param):
|
||
'''Returns a list with numeric index corresponding to field's name'''
|
||
return [self.attributes.index(i) for i in param]
|