Thuban/Model/transientdb.py

# Copyright (C) 2003 by Intevation GmbH
# Authors:
# Bernhard Herzog <[email protected]>
#
# This program is free software under the GPL (>=v2)
# Read the file COPYING coming with the software for details.

"""Database for transient data

This database is intended for data representations needed during the
lifetime of a Thuban session but which is not permanent. Examples of
this are for instance a join of two DBF files where the DBF files are
the permanent representation of the data and the join only exists in the
Thuban session and is reconstructed when the session is opened.
"""

__version__ = "$Revision$"
# $Source$
# $Id$

import os
import weakref
from sqlite import connect

import table

sql_type_map = {
    table.FIELDTYPE_INT: "INTEGER",
    table.FIELDTYPE_STRING: "VARCHAR",
    table.FIELDTYPE_DOUBLE: "FLOAT",
    }

type_converter_map = {
    table.FIELDTYPE_INT: int,
    table.FIELDTYPE_STRING: str,
    table.FIELDTYPE_DOUBLE: float,
    }

class TransientDatabase:

    def __init__(self, filename):
        self.filename = filename
        self.conn = connect(filename)
        # Counters to produce unique table and column names
        self.num_tables = 0
        self.num_cols = 0
        # Since there's only once process using the SQLite database, we
        # might be able to get a tad more speed with default_synchronous
        # OFF. So far I haven't seen any measurable speedup, though.
        #self.execute("PRAGMA default_synchronous = OFF")

    def __del__(self):
        self.close()

    def close(self):
        if self.conn is not None:
            self.conn.close()
            self.conn = None

    def new_table_name(self):
        self.num_tables += 1
        return "Table%03d" % self.num_tables

    def new_column_name(self):
        self.num_cols += 1
        return "Col%03d" % self.num_cols

    def execute(self, *args):
        """execute the SQL statement in the database and return the result"""
        cursor = self.conn.cursor()
        cursor.execute(*args)
        result = cursor.fetchone()
        self.conn.commit()
        return result

    def cursor(self):
        return self.conn.cursor()


class ColumnReference:

    def __init__(self, name, type, internal_name):
        self.name = name
        self.type = type
        self.internal_name = internal_name


class TransientTableBase(table.OldTableInterfaceMixin):

    """Base class for tables in the transient database"""

    def __init__(self, transient_db):
        """Initialize the table for use with the given transient db"""
        self.db = transient_db
        self.tablename = self.db.new_table_name()
        self.indexed_columns = {}
        self.read_record_cursor = None
        self.read_record_last_row = None
        self.read_record_last_result = None

    def create(self, columns):
        self.columns = columns
        self.name_to_column = {}
        self.orig_names = []
        self.internal_to_orig = {}
        self.orig_to_internal = {}
        self.column_map = {}

        # Create the column objects and fill various maps and lists
        for index in range(len(self.columns)):
            col = self.columns[index]
            self.name_to_column[col.name] = col
            self.orig_names.append(col.name)
            self.internal_to_orig[col.internal_name] = col.name
            self.orig_to_internal[col.name] = col.internal_name
            self.column_map[col.name] = col
            self.column_map[index] = col

        # Build the CREATE TABLE statement and create the table in the
        # database
        table_types = ["id INTEGER PRIMARY KEY"]
        for col in self.columns:
            table_types.append("%s %s" % (col.internal_name,
                                          sql_type_map[col.type]))
        table_stmt = "CREATE TABLE %s (\n    %s\n);" % (self.tablename,
                                                   ",\n    ".join(table_types))
        self.db.execute(table_stmt)

    def transient_table(self):
        """
        Return a table whose underlying implementation is in the transient db
        """
        return self

    def ensure_index(self, column):
        """Ensure that there's an index on the given column"""
        if not column in self.indexed_columns:
            internal_name = self.orig_to_internal[column]
            indexname = "Index_%s_%s" % (self.tablename, internal_name)
            stmt = "CREATE INDEX %s ON %s (%s);" % (indexname, self.tablename,
                                                    internal_name)
            self.db.execute(stmt)
            self.indexed_columns[column] = 1

    def NumColumns(self):
        return len(self.columns)

    def NumRows(self):
        result = self.db.execute("SELECT count(*) FROM %s;" % self.tablename)
        return int(result[0])

    def Columns(self):
        return self.columns

    def Column(self, col):
        return self.column_map[col]

    def HasColumn(self, col):
        """Return whether the table has a column with the given name or index
        """
        return self.column_map.has_key(col)

    def ReadRowAsDict(self, index):
        # Implementation Strategy: Executing a completely new select
        # statement every time this method is called is too slow. The
        # most important usage is to read the records more or less
        # sequentially. This happens e.g. when drawing a layer with a
        # classification where the shapes are drawn in order of the
        # shape ids. Another pattern is that the same row is requested
        # several times in a row. This happens in the table view, for
        # instance.

        # We can exploit this to make access faster by having one cursor
        # open all the time and keeping the last row read around in case
        # the same row is accessed again the next time and if the row
        # index is larger than the row we have read last we simply fetch
        # rows from the cursor until we've reached the requested row. If
        # the requested row index is smaller then we start a new cursor.

        # FIXME: So far this scheme seems to work well enough. Obvious
        # improvements would be to start the cursor at exactly the
        # requested row (should be efficient and easy to do now that the
        # id is the primary key) and to perhaps to also start a new
        # cursor if the requested index is much larger than the last row
        # so that we don't read and discard lots of the rows.

        # Check whether we have to start a new cursor
        if self.read_record_cursor is None or index <self.read_record_last_row:
            stmt = ("SELECT %s FROM %s;"
                    % (", ".join([c.internal_name for c in self.columns]),
                       self.tablename))
            self.read_record_cursor = self.db.cursor()
            self.read_record_cursor.execute(stmt)
            self.read_record_last_row = -1
            self.read_record_last_result = None

        # Now we should have a cursor at a position less than or equal
        # to the index so the following if statement will always set
        # result to a suitable value
        assert index >= self.read_record_last_row

        if index == self.read_record_last_row:
            result = self.read_record_last_result
        else:
            for i in range(index - self.read_record_last_row):
                result = self.read_record_cursor.fetchone()
                self.read_record_last_result = result
        self.read_record_last_row = index
        return dict(zip(self.orig_names, result))

    def ReadValue(self, row, col):
        """Return the value of the specified row and column

        The col parameter may be the index of the column or its name.
        """
        # Depending on the actual access patterns of the table data, it
        # might be a bit faster in some circumstances to not implement
        # this via ReadRowAsDict, but this simple implementation should
        # be fast enough for most purposes.
        return self.ReadRowAsDict(row)[self.column_map[col].name]

    def ValueRange(self, col):
        col = self.column_map[col]
        iname = col.internal_name
        min, max = self.db.execute("SELECT min(%s), max(%s) FROM %s;"
                                   % (iname, iname, self.tablename))
        converter = type_converter_map[col.type]
        return (converter(min), converter(max))

    def UniqueValues(self, col):
        iname = self.column_map[col].internal_name
        cursor = self.db.cursor()
        cursor.execute("SELECT %s FROM %s GROUP BY %s;"
                       % (iname, self.tablename, iname))
        result = []
        while 1:
            row = cursor.fetchone()
            if row is None:
                break
            result.append(row[0])
        return result

    def SimpleQuery(self, left, comparison, right):
        """Return the indices of all rows that matching a condition.

        Parameters:
           left -- The column object for the left side of the comparison

           comparison -- The comparison operator as a string. It must be
                         one of '==', '!=', '<', '<=', '>=', '>'

           right -- The right hand side of the comparison. It must be
                    either a column object or a value, i.e. a string,
                    int or float.

        The return value is a sorted list of the indices of the rows
        where the condition is true.
        """
        if comparison not in ("==", "!=", "<", "<=", ">=", ">"):
            raise ValueError("Comparison operator %r not allowed" % comparison)

        if hasattr(right, "internal_name"):
            right_template = right.internal_name
            params = ()
        else:
            right_template = "%s"
            params = (right,)

        query = "SELECT id FROM %s WHERE %s %s %s ORDER BY id;" \
                % (self.tablename, left.internal_name, comparison,
                   right_template)

        cursor = self.db.cursor()
        cursor.execute(query, params)
        result = []
        while 1:
            row = cursor.fetchone()
            if row is None:
                break
            result.append(row[0])
        return result


class TransientTable(TransientTableBase):

    """A Table in a transient DB that starts as the copy of a Thuban Table."""

    def __init__(self, transient_db, table):
        """Create a new table in the given transient DB as a copy of table

        The table argument can be any object implementing the Table
        interface.
        """
        TransientTableBase.__init__(self, transient_db)
        self.create(table)

    def create(self, table):
        columns = []
        for col in table.Columns():
            columns.append(ColumnReference(col.name, col.type,
                                           self.db.new_column_name()))
        TransientTableBase.create(self, columns)

        # copy the input table to the transient db

        # A key to insert to use for the formatting of the insert
        # statement. The key must not be equal to any of the column
        # names so we construct one by building a string of x's that is
        # longer than any of the column names
        id_key = max([len(col.name) for col in self.columns]) * "x"

        insert_template = "INSERT INTO %s (id, %s) VALUES (%%(%s)s, %s);" \
                               % (self.tablename,
                                  ", ".join([col.internal_name
                                             for col in self.columns]),
                                  id_key,
                                  ", ".join(["%%(%s)s" % col.name
                                             for col in self.columns]))
        cursor = self.db.cursor()
        for i in range(table.NumRows()):
            row = table.ReadRowAsDict(i)
            row[id_key] = i
            cursor.execute(insert_template, row)
        self.db.conn.commit()


class TransientJoinedTable(TransientTableBase):

    """A Table in the transient DB that contains a join of two tables"""

    def __init__(self, transient_db, left_table, left_field,
                 right_table, right_field = None):
        """Create a new table in the transient DB as a join of two tables.

        Both input tables, left_table and right_table must have a
        transient_table method that returns a table object for a table
        in the trnsient database. The join is performed on the condition
        that the value of the left_field column the the left table is
        equal to the value of the right_field in the right_table.

        The joined table contains all columns of the input tables with
        one exception: Any column in the right_table with the same name
        as one of the columns in the left_table will be omitted. This is
        somewhat of an implementation detail, but is done so that the
        column names of the joined table can be the same as the column
        names of the input tables without having to create prefixes.
        """
        TransientTableBase.__init__(self, transient_db)
        self.left_table = left_table.transient_table()
        self.left_field = left_field
        self.right_table = right_table.transient_table()
        if right_field:
            self.right_field = right_field
        else:
            self.right_field = self.left_field
        self.create()

    def create(self):
        """Internal: Create the table with the joined data"""
        self.tablename = self.db.new_table_name()

        self.right_table.ensure_index(self.right_field)

        # Coalesce the column information
        visited = {}
        columns = []
        for col in self.left_table.columns + self.right_table.columns:
            if col.name in visited:
                # We can't allow multiple columns with the same original
                # name, so omit this one. FIXME: There should be a
                # better solution.
                continue
            columns.append(col)
        TransientTableBase.create(self, columns)

        # Copy the joined data to the table.
        internal_names = [col.internal_name for col in self.columns]
        stmt = ("INSERT INTO %s (id, %s) SELECT %s.id, %s FROM %s"
                " JOIN %s ON %s = %s;"
                % (self.tablename,
                   ", ".join(internal_names),
                   self.left_table.tablename,
                   ", ".join(internal_names),
                   self.left_table.tablename,
                   self.right_table.tablename,
                   self.orig_to_internal[self.left_field],
                   self.orig_to_internal[self.right_field]))
        self.db.execute(stmt)


class AutoTransientTable(table.OldTableInterfaceMixin):

    """Table that copies data to a transient table on demand.

    The AutoTransientTable takes another table as input and copies data
    to a table in a TransientDatabase instance on demand.
    """

    def __init__(self, transient_db, table):
        self.transient_db = transient_db
        self.table = table
        self.t_table = None

    def Columns(self):
        return self.table.Columns()

    def Column(self, col):
        return self.table.Column(col)

    def HasColumn(self, col):
        """Return whether the table has a column with the given name or index
        """
        return self.table.HasColumn(col)

    def NumRows(self):
        return self.table.NumRows()

    def NumColumns(self):
        return self.table.NumColumns()

    def ReadRowAsDict(self, record):
        """Return the record no. record as a dict mapping field names to values
        """
        if self.t_table is not None:
            return self.t_table.ReadRowAsDict(record)
        else:
            return self.table.ReadRowAsDict(record)

    def ReadValue(self, row, col):
        """Return the value of the specified row and column

        The col parameter may be the index of the column or its name.
        """
        if self.t_table is not None:
            return self.t_table.ReadValue(row, col)
        else:
            return self.table.ReadValue(row, col)

    def copy_to_transient(self):
        """Internal: Create a transient table and copy the data into it"""
        self.t_table = TransientTable(self.transient_db, self)

    def transient_table(self):
        """
        Return a table whose underlying implementation is in the transient db
        """
        if self.t_table is None:
            self.copy_to_transient()
        return self.t_table

    def ValueRange(self, col):
        if self.t_table is None:
            self.copy_to_transient()
        return self.t_table.ValueRange(col)

    def UniqueValues(self, col):
        if self.t_table is None:
            self.copy_to_transient()
        return self.t_table.UniqueValues(col)

    def SimpleQuery(self, left, comparison, right):
        if self.t_table is None:
            self.copy_to_transient()
        # Make sure to use the column object of the transient table. The
        # left argument is always a column object so we can just ask the
        # t_table for the right object.
        return self.t_table.SimpleQuery(self.t_table.Column(left.name),
                                        comparison, right)
1	bh	765	# Copyright (C) 2003 by Intevation GmbH
2			# Authors:
3			# Bernhard Herzog <[email protected]>
4			#
5			# This program is free software under the GPL (>=v2)
6			# Read the file COPYING coming with the software for details.
7
8			"""Database for transient data
9
10			This database is intended for data representations needed during the
11			lifetime of a Thuban session but which is not permanent. Examples of
12			this are for instance a join of two DBF files where the DBF files are
13			the permanent representation of the data and the join only exists in the
14			Thuban session and is reconstructed when the session is opened.
15			"""
16
17			__version__ = "$Revision$"
18			# $Source$
19			# $Id$
20
21			import os
22			import weakref
23			from sqlite import connect
24
25			import table
26
27			sql_type_map = {
28			table.FIELDTYPE_INT: "INTEGER",
29			table.FIELDTYPE_STRING: "VARCHAR",
30			table.FIELDTYPE_DOUBLE: "FLOAT",
31			}
32
33			type_converter_map = {
34			table.FIELDTYPE_INT: int,
35			table.FIELDTYPE_STRING: str,
36			table.FIELDTYPE_DOUBLE: float,
37			}
38
39			class TransientDatabase:
40
41			def __init__(self, filename):
42			self.filename = filename
43			self.conn = connect(filename)
44			# Counters to produce unique table and column names
45			self.num_tables = 0
46			self.num_cols = 0
47			# Since there's only once process using the SQLite database, we
48			# might be able to get a tad more speed with default_synchronous
49			# OFF. So far I haven't seen any measurable speedup, though.
50			#self.execute("PRAGMA default_synchronous = OFF")
51
52			def __del__(self):
53			self.close()
54
55			def close(self):
56	bh	777	if self.conn is not None:
57	bh	765	self.conn.close()
58	bh	777	self.conn = None
59	bh	765
60			def new_table_name(self):
61			self.num_tables += 1
62			return "Table%03d" % self.num_tables
63
64			def new_column_name(self):
65			self.num_cols += 1
66			return "Col%03d" % self.num_cols
67
68			def execute(self, *args):
69			"""execute the SQL statement in the database and return the result"""
70			cursor = self.conn.cursor()
71			cursor.execute(*args)
72			result = cursor.fetchone()
73			self.conn.commit()
74			return result
75
76			def cursor(self):
77			return self.conn.cursor()
78
79
80			class ColumnReference:
81
82			def __init__(self, name, type, internal_name):
83			self.name = name
84			self.type = type
85			self.internal_name = internal_name
86
87
88	bh	818	class TransientTableBase(table.OldTableInterfaceMixin):
89	bh	765
90			"""Base class for tables in the transient database"""
91
92			def __init__(self, transient_db):
93			"""Initialize the table for use with the given transient db"""
94			self.db = transient_db
95			self.tablename = self.db.new_table_name()
96			self.indexed_columns = {}
97			self.read_record_cursor = None
98			self.read_record_last_row = None
99	bh	785	self.read_record_last_result = None
100	bh	765
101			def create(self, columns):
102			self.columns = columns
103			self.name_to_column = {}
104			self.orig_names = []
105			self.internal_to_orig = {}
106			self.orig_to_internal = {}
107	bh	818	self.column_map = {}
108	bh	765
109			# Create the column objects and fill various maps and lists
110	bh	818	for index in range(len(self.columns)):
111			col = self.columns[index]
112	bh	765	self.name_to_column[col.name] = col
113			self.orig_names.append(col.name)
114			self.internal_to_orig[col.internal_name] = col.name
115			self.orig_to_internal[col.name] = col.internal_name
116	bh	818	self.column_map[col.name] = col
117			self.column_map[index] = col
118	bh	765
119			# Build the CREATE TABLE statement and create the table in the
120			# database
121	bh	841	table_types = ["id INTEGER PRIMARY KEY"]
122	bh	765	for col in self.columns:
123			table_types.append("%s %s" % (col.internal_name,
124			sql_type_map[col.type]))
125			table_stmt = "CREATE TABLE %s (\n %s\n);" % (self.tablename,
126			",\n ".join(table_types))
127			self.db.execute(table_stmt)
128
129			def transient_table(self):
130			"""
131			Return a table whose underlying implementation is in the transient db
132			"""
133			return self
134
135			def ensure_index(self, column):
136			"""Ensure that there's an index on the given column"""
137			if not column in self.indexed_columns:
138			internal_name = self.orig_to_internal[column]
139			indexname = "Index_%s_%s" % (self.tablename, internal_name)
140			stmt = "CREATE INDEX %s ON %s (%s);" % (indexname, self.tablename,
141			internal_name)
142			self.db.execute(stmt)
143			self.indexed_columns[column] = 1
144
145	bh	818	def NumColumns(self):
146	bh	765	return len(self.columns)
147
148	bh	818	def NumRows(self):
149	bh	765	result = self.db.execute("SELECT count(*) FROM %s;" % self.tablename)
150			return int(result[0])
151
152	bh	818	def Columns(self):
153			return self.columns
154
155			def Column(self, col):
156			return self.column_map[col]
157
158	bh	839	def HasColumn(self, col):
159			"""Return whether the table has a column with the given name or index
160			"""
161			return self.column_map.has_key(col)
162
163	bh	818	def ReadRowAsDict(self, index):
164	bh	849	# Implementation Strategy: Executing a completely new select
165			# statement every time this method is called is too slow. The
166			# most important usage is to read the records more or less
167			# sequentially. This happens e.g. when drawing a layer with a
168			# classification where the shapes are drawn in order of the
169			# shape ids. Another pattern is that the same row is requested
170			# several times in a row. This happens in the table view, for
171			# instance.
172
173			# We can exploit this to make access faster by having one cursor
174			# open all the time and keeping the last row read around in case
175			# the same row is accessed again the next time and if the row
176			# index is larger than the row we have read last we simply fetch
177			# rows from the cursor until we've reached the requested row. If
178			# the requested row index is smaller then we start a new cursor.
179
180			# FIXME: So far this scheme seems to work well enough. Obvious
181			# improvements would be to start the cursor at exactly the
182			# requested row (should be efficient and easy to do now that the
183			# id is the primary key) and to perhaps to also start a new
184			# cursor if the requested index is much larger than the last row
185			# so that we don't read and discard lots of the rows.
186
187			# Check whether we have to start a new cursor
188	bh	765	if self.read_record_cursor is None or index <self.read_record_last_row:
189			stmt = ("SELECT %s FROM %s;"
190			% (", ".join([c.internal_name for c in self.columns]),
191			self.tablename))
192			self.read_record_cursor = self.db.cursor()
193			self.read_record_cursor.execute(stmt)
194			self.read_record_last_row = -1
195	bh	785	self.read_record_last_result = None
196
197			# Now we should have a cursor at a position less than or equal
198			# to the index so the following if statement will always set
199			# result to a suitable value
200			assert index >= self.read_record_last_row
201
202			if index == self.read_record_last_row:
203	bh	818	result = self.read_record_last_result
204	bh	785	else:
205			for i in range(index - self.read_record_last_row):
206			result = self.read_record_cursor.fetchone()
207			self.read_record_last_result = result
208	bh	765	self.read_record_last_row = index
209	bh	785	return dict(zip(self.orig_names, result))
210	bh	765
211	bh	849	def ReadValue(self, row, col):
212			"""Return the value of the specified row and column
213
214			The col parameter may be the index of the column or its name.
215			"""
216			# Depending on the actual access patterns of the table data, it
217			# might be a bit faster in some circumstances to not implement
218			# this via ReadRowAsDict, but this simple implementation should
219			# be fast enough for most purposes.
220			return self.ReadRowAsDict(row)[self.column_map[col].name]
221
222	bh	818	def ValueRange(self, col):
223			col = self.column_map[col]
224	bh	765	iname = col.internal_name
225			min, max = self.db.execute("SELECT min(%s), max(%s) FROM %s;"
226			% (iname, iname, self.tablename))
227			converter = type_converter_map[col.type]
228	bh	818	return (converter(min), converter(max))
229	bh	765
230	bh	818	def UniqueValues(self, col):
231			iname = self.column_map[col].internal_name
232	bh	765	cursor = self.db.cursor()
233			cursor.execute("SELECT %s FROM %s GROUP BY %s;"
234			% (iname, self.tablename, iname))
235			result = []
236			while 1:
237			row = cursor.fetchone()
238			if row is None:
239			break
240			result.append(row[0])
241			return result
242
243	bh	841	def SimpleQuery(self, left, comparison, right):
244			"""Return the indices of all rows that matching a condition.
245	bh	765
246	bh	841	Parameters:
247			left -- The column object for the left side of the comparison
248
249			comparison -- The comparison operator as a string. It must be
250			one of '==', '!=', '<', '<=', '>=', '>'
251
252			right -- The right hand side of the comparison. It must be
253			either a column object or a value, i.e. a string,
254			int or float.
255
256			The return value is a sorted list of the indices of the rows
257			where the condition is true.
258			"""
259			if comparison not in ("==", "!=", "<", "<=", ">=", ">"):
260			raise ValueError("Comparison operator %r not allowed" % comparison)
261
262			if hasattr(right, "internal_name"):
263			right_template = right.internal_name
264			params = ()
265			else:
266			right_template = "%s"
267			params = (right,)
268
269			query = "SELECT id FROM %s WHERE %s %s %s ORDER BY id;" \
270			% (self.tablename, left.internal_name, comparison,
271			right_template)
272
273			cursor = self.db.cursor()
274			cursor.execute(query, params)
275			result = []
276			while 1:
277			row = cursor.fetchone()
278			if row is None:
279			break
280			result.append(row[0])
281			return result
282
283
284	bh	765	class TransientTable(TransientTableBase):
285
286			"""A Table in a transient DB that starts as the copy of a Thuban Table."""
287
288			def __init__(self, transient_db, table):
289			"""Create a new table in the given transient DB as a copy of table
290
291			The table argument can be any object implementing the Table
292			interface.
293			"""
294			TransientTableBase.__init__(self, transient_db)
295			self.create(table)
296
297			def create(self, table):
298			columns = []
299	bh	818	for col in table.Columns():
300			columns.append(ColumnReference(col.name, col.type,
301	bh	765	self.db.new_column_name()))
302			TransientTableBase.create(self, columns)
303
304			# copy the input table to the transient db
305	bh	841
306			# A key to insert to use for the formatting of the insert
307			# statement. The key must not be equal to any of the column
308			# names so we construct one by building a string of x's that is
309			# longer than any of the column names
310			id_key = max([len(col.name) for col in self.columns]) * "x"
311
312			insert_template = "INSERT INTO %s (id, %s) VALUES (%%(%s)s, %s);" \
313	bh	765	% (self.tablename,
314			", ".join([col.internal_name
315			for col in self.columns]),
316	bh	841	id_key,
317	bh	765	", ".join(["%%(%s)s" % col.name
318			for col in self.columns]))
319			cursor = self.db.cursor()
320	bh	818	for i in range(table.NumRows()):
321	bh	841	row = table.ReadRowAsDict(i)
322			row[id_key] = i
323			cursor.execute(insert_template, row)
324	bh	765	self.db.conn.commit()
325
326
327
328			class TransientJoinedTable(TransientTableBase):
329
330			"""A Table in the transient DB that contains a join of two tables"""
331
332			def __init__(self, transient_db, left_table, left_field,
333			right_table, right_field = None):
334			"""Create a new table in the transient DB as a join of two tables.
335
336			Both input tables, left_table and right_table must have a
337			transient_table method that returns a table object for a table
338			in the trnsient database. The join is performed on the condition
339			that the value of the left_field column the the left table is
340			equal to the value of the right_field in the right_table.
341
342			The joined table contains all columns of the input tables with
343			one exception: Any column in the right_table with the same name
344			as one of the columns in the left_table will be omitted. This is
345			somewhat of an implementation detail, but is done so that the
346			column names of the joined table can be the same as the column
347			names of the input tables without having to create prefixes.
348			"""
349			TransientTableBase.__init__(self, transient_db)
350			self.left_table = left_table.transient_table()
351			self.left_field = left_field
352			self.right_table = right_table.transient_table()
353			if right_field:
354			self.right_field = right_field
355			else:
356			self.right_field = self.left_field
357			self.create()
358
359			def create(self):
360			"""Internal: Create the table with the joined data"""
361			self.tablename = self.db.new_table_name()
362
363			self.right_table.ensure_index(self.right_field)
364
365			# Coalesce the column information
366			visited = {}
367			columns = []
368			for col in self.left_table.columns + self.right_table.columns:
369			if col.name in visited:
370	bh	841	# We can't allow multiple columns with the same original
371			# name, so omit this one. FIXME: There should be a
372			# better solution.
373	bh	765	continue
374			columns.append(col)
375			TransientTableBase.create(self, columns)
376
377			# Copy the joined data to the table.
378			internal_names = [col.internal_name for col in self.columns]
379	bh	841	stmt = ("INSERT INTO %s (id, %s) SELECT %s.id, %s FROM %s"
380			" JOIN %s ON %s = %s;"
381			% (self.tablename,
382			", ".join(internal_names),
383			self.left_table.tablename,
384			", ".join(internal_names),
385			self.left_table.tablename,
386			self.right_table.tablename,
387			self.orig_to_internal[self.left_field],
388			self.orig_to_internal[self.right_field]))
389	bh	765	self.db.execute(stmt)
390
391
392	bh	818	class AutoTransientTable(table.OldTableInterfaceMixin):
393	bh	765
394			"""Table that copies data to a transient table on demand.
395
396			The AutoTransientTable takes another table as input and copies data
397			to a table in a TransientDatabase instance on demand.
398			"""
399
400			def __init__(self, transient_db, table):
401			self.transient_db = transient_db
402			self.table = table
403			self.t_table = None
404
405	bh	818	def Columns(self):
406			return self.table.Columns()
407	bh	765
408	bh	818	def Column(self, col):
409			return self.table.Column(col)
410	bh	765
411	bh	839	def HasColumn(self, col):
412			"""Return whether the table has a column with the given name or index
413			"""
414			return self.table.HasColumn(col)
415
416	bh	818	def NumRows(self):
417			return self.table.NumRows()
418	bh	765
419	bh	818	def NumColumns(self):
420			return self.table.NumColumns()
421	bh	765
422	bh	818	def ReadRowAsDict(self, record):
423	bh	765	"""Return the record no. record as a dict mapping field names to values
424			"""
425			if self.t_table is not None:
426	bh	839	return self.t_table.ReadRowAsDict(record)
427	bh	765	else:
428	bh	818	return self.table.ReadRowAsDict(record)
429	bh	765
430	bh	849	def ReadValue(self, row, col):
431			"""Return the value of the specified row and column
432
433			The col parameter may be the index of the column or its name.
434			"""
435			if self.t_table is not None:
436			return self.t_table.ReadValue(row, col)
437			else:
438			return self.table.ReadValue(row, col)
439
440	bh	765	def copy_to_transient(self):
441			"""Internal: Create a transient table and copy the data into it"""
442			self.t_table = TransientTable(self.transient_db, self)
443
444			def transient_table(self):
445			"""
446			Return a table whose underlying implementation is in the transient db
447			"""
448			if self.t_table is None:
449			self.copy_to_transient()
450			return self.t_table
451
452	bh	818	def ValueRange(self, col):
453	bh	765	if self.t_table is None:
454			self.copy_to_transient()
455	bh	839	return self.t_table.ValueRange(col)
456	bh	765
457	bh	839	def UniqueValues(self, col):
458	bh	765	if self.t_table is None:
459			self.copy_to_transient()
460	bh	839	return self.t_table.UniqueValues(col)
461	bh	844
462			def SimpleQuery(self, left, comparison, right):
463			if self.t_table is None:
464			self.copy_to_transient()
465			# Make sure to use the column object of the transient table. The
466			# left argument is always a column object so we can just ask the
467			# t_table for the right object.
468			return self.t_table.SimpleQuery(self.t_table.Column(left.name),
469			comparison, right)
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