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
from Thuban.common import *

# 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 field_info_by_name(self, fieldName):
        count = self.field_count()

        for i in range(count):
            info = self.field_info(i)
            if info[1] == fieldName:
                return info

        return None

    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	# Copyright (c) 2001, 2002 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 Thuban for details.
7
8	"""
9	Classes for handling tables of data.
10	"""
11
12	__version__ = "$Revision$"
13
14	import dbflib
15	from Thuban.common import *
16
17	# the field types supported by a Table instance.
18	FIELDTYPE_INT = "int"
19	FIELDTYPE_STRING = "string"
20	FIELDTYPE_DOUBLE = "double"
21
22
23	# map the dbflib constants for the field types to our constants
24	dbflib_fieldtypes = {dbflib.FTString: FIELDTYPE_STRING,
25	dbflib.FTInteger: FIELDTYPE_INT,
26	dbflib.FTDouble: FIELDTYPE_DOUBLE}
27
28	class Table:
29
30	"""
31	Represent a table of data.
32
33	Currently this is basically just a wrapper around dbflib.
34	"""
35
36	# Implementation strategy regarding writing to a DBF file:
37	#
38	# Most of the time Thuban only needs to read from a table and it is
39	# important that Thuban can work with read-only files. Therefore the
40	# DBF file is opened only for reading initially. Only when
41	# write_record is called we try to open the DBF file for writing as
42	# well. If that succeeds the dbf read/write DBF file will be used
43	# for all IO afterwards.
44	#
45	# It's important to use the same DBF file object for both reading
46	# and writing to make sure that reading a records after writing
47	# returns the new values. With two separate objects this wouldn't
48	# work because a DBF file object buffers some data
49
50	def __init__(self, filename):
51	self.filename = filename
52	self.dbf = dbflib.DBFFile(filename)
53
54	# If true, self.dbf is open for writing.
55	self._writable = 0
56
57	def Destroy(self):
58	self.dbf.close()
59	self.dbf = None
60
61	def record_count(self):
62	"""Return the number of records"""
63	return self.dbf.record_count()
64
65	def field_count(self):
66	"""Return the number of fields in a record"""
67	return self.dbf.field_count()
68
69	def field_info(self, field):
70	"""Return a tuple (type, name, width, prec) for the field no. field
71
72	type is the data type of the field, name the name, width the
73	field width in characters and prec the decimal precision.
74	"""
75	type, name, width, prec = self.dbf.field_info(field)
76	type = dbflib_fieldtypes[type]
77	return type, name, width, prec
78
79	def field_info_by_name(self, fieldName):
80	count = self.field_count()
81
82	for i in range(count):
83	info = self.field_info(i)
84	if info[1] == fieldName:
85	return info
86
87	return None
88
89	def read_record(self, record):
90	"""Return the record no. record as a dict mapping field names to values
91	"""
92	return self.dbf.read_record(record)
93
94	def write_record(self, record, values):
95	"""Write the values into the record
96
97	The values parameter may either be a dictionary or a sequence.
98
99	If it's a dictionary the keys must be the names of the fields
100	and their value must have a suitable type. Only the fields
101	actually contained in the dictionary are written. Fields for
102	which there's no item in the dict are not modified.
103
104	If it's a sequence, all fields must be present in the right
105	order.
106	"""
107	if not self._writable:
108	new_dbf = dbflib.DBFFile(self.filename, "r+b")
109	self.dbf.close()
110	self.dbf = new_dbf
111	self._writable = 1
112	self.dbf.write_record(record, values)
113	self.dbf.commit()
114
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