Source Code for Module vtab_media

  1  ### BITPIM 
  2  ### 
  3  ### Copyright (C) 2007 Joe Pham <djpham@bitpim.org> 
  4  ### 
  5  ### This program is free software; you can redistribute it and/or modify 
  6  ### it under the terms of the BitPim license as detailed in the LICENSE file. 
  7  ### 
  8  ### $Id: vtab_media.py 4155 2007-03-17 04:07:42Z djpham $ 
  9   
 10  """ 
 11  An apsw compatible module that implements a virtual table that stores media 
 12  data as native system files. 
 13  """ 
 14  # System modules 
 15  import glob 
 16  import os 
 17  import os.path 
 18   
 19  # BitPim moduless 
 20  import database 
 21   
 22 -class Media(database.ModuleBase): 
 23      """ 
 24      Module to implements a virtual table that stores media data as native system 
 25      files. 
 26      The table has 2 fiels: __rowid__ and mediadata 
 27      This class maintains its own rowid, cursor, and constraints parameters. 
 28      The data of each row is stored in a file named Fxxxxxxx, where 
 29      xxxxxxx is the rowid starting with 1 ie (F0000001, F0000002, etc) 
 30      """ 
 31   
 32 -    def __init__(self, pathname): 
 33          """ 
 34          @params pathname: full path in which to stores data files 
 35          """ 
 36          super(Media, self).__init__(('data',)) 
 37          # make sure the path exists 
 38          if not os.path.exists(pathname): 
 39              os.makedirs(pathname) 
 40          self.pathname=os.path.abspath(pathname) 
 41          self.rowidfilename=os.path.join(self.pathname, 'rowid') 
 42          self.getnextrowid() 
 43          self.filenames=[] 
 44          self.cursor=None 
 45   
 46 -    def getnextrowid(self): 
 47          """ 
 48          Return the next row ID from a file called rowid 
 49          """ 
 50          try: 
 51              id=file(self.rowidfilename, 'rt').read() 
 52              self.rowid=int(id) 
 53          except IOError: 
 54              # file does not exist 
 55              self.rowid=1 
 56              self.saverowid(1) 
 57 -    def incrementrowid(self): 
 58          # increment the next row ID by 1 
 59          self.rowid+=1 
 60          self.saverowid(self.rowid) 
 61 -    def saverowid(self, id): 
 62          file(self.rowidfilename, 'wt').write(str(id)) 
 63 -    def filenamefromid(self, id): 
 64          # return a full path name based on the row ID 
 65          return os.path.join(self.pathname, 'F%07d'%id) 
 66 -    def idfromfilename(self, filename): 
 67          return int(os.path.basename(filename)[1:]) 
 68   
 69 -    def BestIndex(self, constraints, orderby): 
 70          """ 
 71          Provide information on how to best access this table. 
 72          Must be overriden by subclass. 
 73          @params constraints: a tuple of (column #, op) defining a constraints 
 74          @params orderby: a tuple of (column #, desc) defining the order by 
 75          @returns a tuple of up to 5 values: 
 76              0: aConstraingUsage: a tuple of the same size as constraints. 
 77                  Each item is either None, argv index(int), or (argv index, omit(Bool)). 
 78              1: idxNum(int) 
 79              2: idxStr(string) 
 80              3: orderByConsumed(Bool) 
 81              4: estimatedCost(float) 
 82   
 83          Todo: store the constraints for subsequent evaluation, and tell 
 84              sqlite to pass the constraints parameters to Filter. 
 85          """ 
 86          pass 
 87 -    def Filter(self, idxNum, idxStr, argv): 
 88          """ 
 89          Begin a search of a virtual table. 
 90          @params idxNum: int value passed by BestIndex 
 91          @params idxStr: string valued passed by BestIndex 
 92          @params argv: constraint parameters requested by BestIndex 
 93          @returns: None 
 94   
 95          Todo: evaluate actual constraints, will let sqlite do the orderby. 
 96          """ 
 97          self.filenames=glob.glob(os.path.join(self.pathname, 
 98                                                'F[0-9][0-9][0-9][0-9][0-9][0-9][0-9]')) 
 99          if self.filenames: 
100              self.cursor=0 
101          else: 
102              self.cursor=None 
103 -    def Eof(self): 
104          """ 
105          Determines if the current cursor points to a valid row. 
106          @returns: False if valid row, True otherwise 
107          """ 
108          return self.cursor is None or self.cursor>=len(self.filenames) 
109 -    def Column(self, N): 
110          """ 
111          Find the value for the N-th column of the current row. 
112          @params N: the N-th column 
113          @returns: value of the N-th column 
114          We only have 2 columns: __rowid__ and mediadata 
115          """ 
116          filename=self.filenames[self.cursor] 
117          if N==0: 
118              # __rowid__ 
119              return self.idfromfilename(filename) 
120          else: 
121              # mediadata 
122              return buffer(file(filename, 'rb').read()) 
123 -    def Next(self): 
124          """ 
125          Move the cursor to the next row. 
126          @returns: None 
127          """ 
128          self.cursor+=1 
129 -    def Rowid(self): 
130          """ 
131          Return the rowid of the current row. 
132          @returns: the rowid(int) of the current row. 
133          """ 
134          return self.Column(0) 
135 -    def UpdateDeleteRow(self, rowid): 
136          """ 
137          Delete row rowid 
138          @params rowid: rowid to delete 
139          @returns: None 
140          """ 
141          # delete the file 
142          os.remove(self.filenamefromid(rowid)) 
143 -    def UpdateInsertRow(self, rowid, fields): 
144          """ 
145          Insert a new row of data into the table 
146          @params rowid: if not None, use this rowid.  If None, create a new rowid 
147          @params fields: a tuple of the field values in the order declared in 
148              Create/Connet 
149          @returns: rowid of the new row. 
150          """ 
151          if rowid is None: 
152              rowid=self.rowid 
153              self.incrementrowid() 
154          file(self.filenamefromid(rowid), 'wb').write(fields[1]) 
155          return rowid 
156 -    def UpdateChangeRow(self, rowid, newrowid, fields): 
157          """ 
158          Change the row of the current rowid with the new rowid and new values 
159          @params rowid: rowid of the current row 
160          @params newrowid: new rowid 
161          @params fields: a tuple of the field values in the order declared in 
162              Create/Connect 
163          @returns: rowid of the new row 
164          """ 
165          os.remove(self.filenamefromid(rowid)) 
166          file(self.filenamefromid(newrowid), 'wb').write(fields[1]) 
167          return newrowid 
168