100 lines
2.7 KiB
Python
100 lines
2.7 KiB
Python
# Relational
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# Copyright (C) 2016 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 splits a query into a program.
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from relational import parser
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class Program:
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def __init__(self, rels):
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self.queries = []
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self.dictionary = {} # Key is the query, value is the relation
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self.vgen = vargen(rels, 'optm_')
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def __str__(self):
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r = ''
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for q in self.queries:
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r += '%s = %s' % (q[0], q[1]) + '\n'
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return r.rstrip()
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def append_query(self, node):
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strnode = str(node)
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rel = self.dictionary.get(strnode)
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if rel:
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return rel
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qname = next(self.vgen)
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self.queries.append((qname, node))
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n = parser.Node()
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n.kind = parser.RELATION
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n.name = qname
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self.dictionary[strnode] = n
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return n
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def _separate(node, program):
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if node.kind == parser.UNARY and node.child.kind != parser.RELATION:
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_separate(node.child, program)
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rel = program.append_query(node.child)
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node.child = rel
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elif node.kind == parser.BINARY:
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if node.left.kind != parser.RELATION:
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_separate(node.left, program)
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rel = program.append_query(node.left)
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node.left = rel
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if node.right.kind != parser.RELATION:
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_separate(node.right, program)
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rel = program.append_query(node.right)
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node.right = rel
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program.append_query(node)
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def vargen(avoid, prefix=''):
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'''
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Generates temp variables.
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Avoid contains variable names to skip.
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'''
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count = 0
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while True:
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r = ''
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c = count
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while True:
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r = chr((c % 26) + 97) + r
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if c < 26:
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break
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c //= 26
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r = prefix + r
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if r not in avoid:
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yield r
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count += 1
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def split(node, rels):
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'''
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Split a query into a program.
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The idea is that if there are duplicated subdtrees they
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get executed only once.
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'''
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p = Program(rels)
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_separate(node, p)
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return str(p)
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