Thuban/Model/table.py

# Copyright (c) 2001, 2002 by Intevation GmbH
# Authors:
# Bernhard Herzog <[email protected]>
#
# This program is free software under the GPL (>=v2)
# Read the file COPYING coming with Thuban for details.

"""
Classes for handling tables of data.
"""

__version__ = "$Revision$"

import dbflib

# the field types supported by a Table instance.
FIELDTYPE_INT = "int"
FIELDTYPE_STRING = "string"
FIELDTYPE_DOUBLE = "double"


# map the dbflib constants for the field types to our constants
dbflib_fieldtypes = {dbflib.FTString: FIELDTYPE_STRING,
                     dbflib.FTInteger: FIELDTYPE_INT,
                     dbflib.FTDouble: FIELDTYPE_DOUBLE}

class Table:

    """
    Represent a table of data.

    Currently this is basically just a wrapper around dbflib.
    """

    # Implementation strategy regarding writing to a DBF file:
    #
    # Most of the time Thuban only needs to read from a table and it is
    # important that Thuban can work with read-only files. Therefore the
    # DBF file is opened only for reading initially. Only when
    # write_record is called we try to open the DBF file for writing as
    # well. If that succeeds the dbf read/write DBF file will be used
    # for all IO afterwards.
    #
    # It's important to use the same DBF file object for both reading
    # and writing to make sure that reading a records after writing
    # returns the new values. With two separate objects this wouldn't
    # work because a DBF file object buffers some data

    def __init__(self, filename):
        self.filename = filename
        self.dbf = dbflib.DBFFile(filename)

        # If true, self.dbf is open for writing.
        self._writable = 0

    def Destroy(self):
        self.dbf.close()
        self.dbf = None

    def record_count(self):
        """Return the number of records"""
        return self.dbf.record_count()

    def field_count(self):
        """Return the number of fields in a record"""
        return self.dbf.field_count()

    def field_info(self, field):
        """Return a tuple (type, name, width, prec) for the field no. field

        type is the data type of the field, name the name, width the
        field width in characters and prec the decimal precision.
        """
        type, name, width, prec = self.dbf.field_info(field)
        type = dbflib_fieldtypes[type]
        return type, name, width, prec

    def read_record(self, record):
        """Return the record no. record as a dict mapping field names to values
        """
        return self.dbf.read_record(record)

    def write_record(self, record, values):
        """Write the values into the record

        The values parameter may either be a dictionary or a sequence.

        If it's a dictionary the keys must be the names of the fields
        and their value must have a suitable type. Only the fields
        actually contained in the dictionary are written. Fields for
        which there's no item in the dict are not modified.

        If it's a sequence, all fields must be present in the right
        order.
        """
        if not self._writable:
            new_dbf = dbflib.DBFFile(self.filename, "r+b")
            self.dbf.close()
            self.dbf = new_dbf
            self._writable = 1
        self.dbf.write_record(record, values)
        self.dbf.commit()
1	bh	257	# Copyright (c) 2001, 2002 by Intevation GmbH
2	bh	6	# Authors:
3			# Bernhard Herzog <[email protected]>
4			#
5			# This program is free software under the GPL (>=v2)
6			# Read the file COPYING coming with Thuban for details.
7
8			"""
9			Classes for handling tables of data.
10			"""
11
12			__version__ = "$Revision$"
13
14			import dbflib
15
16			# the field types supported by a Table instance.
17			FIELDTYPE_INT = "int"
18			FIELDTYPE_STRING = "string"
19			FIELDTYPE_DOUBLE = "double"
20
21
22			# map the dbflib constants for the field types to our constants
23			dbflib_fieldtypes = {dbflib.FTString: FIELDTYPE_STRING,
24			dbflib.FTInteger: FIELDTYPE_INT,
25			dbflib.FTDouble: FIELDTYPE_DOUBLE}
26
27			class Table:
28
29			"""
30			Represent a table of data.
31
32			Currently this is basically just a wrapper around dbflib.
33			"""
34
35	bh	286	# Implementation strategy regarding writing to a DBF file:
36			#
37			# Most of the time Thuban only needs to read from a table and it is
38			# important that Thuban can work with read-only files. Therefore the
39			# DBF file is opened only for reading initially. Only when
40			# write_record is called we try to open the DBF file for writing as
41			# well. If that succeeds the dbf read/write DBF file will be used
42			# for all IO afterwards.
43			#
44			# It's important to use the same DBF file object for both reading
45			# and writing to make sure that reading a records after writing
46			# returns the new values. With two separate objects this wouldn't
47			# work because a DBF file object buffers some data
48
49	bh	6	def __init__(self, filename):
50			self.filename = filename
51	bh	284	self.dbf = dbflib.DBFFile(filename)
52	bh	6
53	bh	286	# If true, self.dbf is open for writing.
54			self._writable = 0
55
56	bh	257	def Destroy(self):
57			self.dbf.close()
58			self.dbf = None
59
60	bh	6	def record_count(self):
61			"""Return the number of records"""
62			return self.dbf.record_count()
63
64			def field_count(self):
65			"""Return the number of fields in a record"""
66			return self.dbf.field_count()
67
68			def field_info(self, field):
69			"""Return a tuple (type, name, width, prec) for the field no. field
70
71			type is the data type of the field, name the name, width the
72			field width in characters and prec the decimal precision.
73			"""
74			type, name, width, prec = self.dbf.field_info(field)
75			type = dbflib_fieldtypes[type]
76			return type, name, width, prec
77
78			def read_record(self, record):
79			"""Return the record no. record as a dict mapping field names to values
80			"""
81			return self.dbf.read_record(record)
82
83	bh	274	def write_record(self, record, values):
84			"""Write the values into the record
85
86			The values parameter may either be a dictionary or a sequence.
87
88			If it's a dictionary the keys must be the names of the fields
89			and their value must have a suitable type. Only the fields
90			actually contained in the dictionary are written. Fields for
91			which there's no item in the dict are not modified.
92
93			If it's a sequence, all fields must be present in the right
94			order.
95			"""
96	bh	286	if not self._writable:
97			new_dbf = dbflib.DBFFile(self.filename, "r+b")
98			self.dbf.close()
99			self.dbf = new_dbf
100			self._writable = 1
101			self.dbf.write_record(record, values)
102			self.dbf.commit()
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