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.
        if hasattr(right, "name"):
            return self.t_table.SimpleQuery(self.t_table.Column(left.name),
                                            comparison, 
                                            self.t_table.Column(right.name))
        else:
            return self.t_table.SimpleQuery(self.t_table.Column(left.name),
                                            comparison, right)
1	# 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	if self.conn is not None:
57	self.conn.close()
58	self.conn = None
59
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	class TransientTableBase(table.OldTableInterfaceMixin):
89
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	self.read_record_last_result = None
100
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	self.column_map = {}
108
109	# Create the column objects and fill various maps and lists
110	for index in range(len(self.columns)):
111	col = self.columns[index]
112	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	self.column_map[col.name] = col
117	self.column_map[index] = col
118
119	# Build the CREATE TABLE statement and create the table in the
120	# database
121	table_types = ["id INTEGER PRIMARY KEY"]
122	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	def NumColumns(self):
146	return len(self.columns)
147
148	def NumRows(self):
149	result = self.db.execute("SELECT count(*) FROM %s;" % self.tablename)
150	return int(result[0])
151
152	def Columns(self):
153	return self.columns
154
155	def Column(self, col):
156	return self.column_map[col]
157
158	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	def ReadRowAsDict(self, index):
164	# 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	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	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	result = self.read_record_last_result
204	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	self.read_record_last_row = index
209	return dict(zip(self.orig_names, result))
210
211	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	def ValueRange(self, col):
223	col = self.column_map[col]
224	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	return (converter(min), converter(max))
229
230	def UniqueValues(self, col):
231	iname = self.column_map[col].internal_name
232	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	def SimpleQuery(self, left, comparison, right):
244	"""Return the indices of all rows that matching a condition.
245
246	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	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	for col in table.Columns():
300	columns.append(ColumnReference(col.name, col.type,
301	self.db.new_column_name()))
302	TransientTableBase.create(self, columns)
303
304	# copy the input table to the transient db
305
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	% (self.tablename,
314	", ".join([col.internal_name
315	for col in self.columns]),
316	id_key,
317	", ".join(["%%(%s)s" % col.name
318	for col in self.columns]))
319	cursor = self.db.cursor()
320	for i in range(table.NumRows()):
321	row = table.ReadRowAsDict(i)
322	row[id_key] = i
323	cursor.execute(insert_template, row)
324	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	# 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	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	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	self.db.execute(stmt)
390
391
392	class AutoTransientTable(table.OldTableInterfaceMixin):
393
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	def Columns(self):
406	return self.table.Columns()
407
408	def Column(self, col):
409	return self.table.Column(col)
410
411	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	def NumRows(self):
417	return self.table.NumRows()
418
419	def NumColumns(self):
420	return self.table.NumColumns()
421
422	def ReadRowAsDict(self, record):
423	"""Return the record no. record as a dict mapping field names to values
424	"""
425	if self.t_table is not None:
426	return self.t_table.ReadRowAsDict(record)
427	else:
428	return self.table.ReadRowAsDict(record)
429
430	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	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	def ValueRange(self, col):
453	if self.t_table is None:
454	self.copy_to_transient()
455	return self.t_table.ValueRange(col)
456
457	def UniqueValues(self, col):
458	if self.t_table is None:
459	self.copy_to_transient()
460	return self.t_table.UniqueValues(col)
461
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	if hasattr(right, "name"):
469	return self.t_table.SimpleQuery(self.t_table.Column(left.name),
470	comparison,
471	self.t_table.Column(right.name))
472	else:
473	return self.t_table.SimpleQuery(self.t_table.Column(left.name),
474	comparison, right)
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