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metakitBrowse.py

#!/usr/bin/python

__version__="$Revision $"[11:-2]
__date__="$Date $"
__author__="Andy Todd <andy47@halfcooked.com>"

#jm - marked changes 030218

"""
Module Name: metakitBrowse
Description: Plug in for PythonCard application dbBrowse to provide MetaKit specific functionality

Constant/configuration values are currently maintained in the source code. If we are to optimise this application they should be split into seperate configuration files (as per PythonCard/Webware style guidelines)

The structure of this module should be replicated for different RDBMS so that they can be interchanged by dbBrowse - hopefully.

To Do;
  Because metakit isn't a relational database we probably don't need to support the getQueryString method in this class. Its only really an internal utility method for the other, public, classes anyway.
"""

import metakit
import os

class browse:

    # Connection should be a dictionary with at least two keys, 
    # 'databasename' and 'directory'
    # This is wildly different to other database modules 
    def __init__(self, connection):
        "Setup the database connection"
        self._system_tables=[]
        # Not providing a db name is guaranteed to ruin our connection
        if not connection['databasename']:
            raise ValueError
        filename = os.path.join(connection['directory'], connection['databasename'])
        # not sure about the mode to use, I assume we just want read-only
        self._db = metakit.storage(filename, 0)
        self._cursor='placeholder'
        # This one is used in getRow
        self._tableName=''

    def getTables(self):
        "Return a list of all of the non-system tables in <database>"
        return [p.name for p in self._db.contents().structure() if p.type == 'V']    #jm

    def getColumns(self, tableName):
        "Get the definition of the columns in tableName"
        columnDefs = []
        for column in self._db.view(tableName).structure():      #jm - this block
            columnName, dataType = column.name,column.type
            if dataType in  ['S','V']:
                dataType == 'varchar'
            elif dataType == 'I':
                dataType == 'int'
            elif dataType in ["F","D"]:
                dataType == 'float'
            nullable, key, default  = "", "", ""
            # Dodgy default, but if works for me
            precision = 25
            columnDefs.append((columnName, dataType, precision, nullable, key, default))
        return columnDefs

    def getQueryString(self, tableName):
        "Return a SQL statement which queries all of the columns in tableName"
        tableStructure=self.getColumns(tableName)
        # Construct and return the string
        stmt='SELECT '
        for columnList in tableStructure:
            stmt+=columnList[0]+', '
        stmt=stmt[:-2]+' FROM '+tableName
        return stmt

    def getRow(self, tableName):
        "Get a row from tableName"
        # When we upgrade to 2.2 this will be a great candidate for a
        # generator/iterator. In the meantime we use self._tableName to keep
        # track of what we are doing
        if tableName!=self._tableName:
            self._tableName=tableName
            self._cursor = self._db.view(tableName)
            self._currentPos = -1

        self._currentPos += 1
        if self._currentPos == len(self._cursor):
            self._currentPos -= 1
            return None

        # could cache these
        # apparently we don't need all the junk info
        # from getColumns nor do we need to use getQueryString
        columnNames = [i.name for i in self._cursor.structure()]    #jm
        row = self._cursor[self._currentPos]
        result = []
        for c in columnNames:
            try:
                result.append(getattr(row, c))
            except:
                result.append('')
        #print result
        return result

    def getRows(self, tableName):
        "Get all of the rows from tableName"
        # columnNames = [i[0] for i in self.getColumns(tableName)]
        self._cursor=self._db.view(tableName)
        columnNames = [i.name for i in self._cursor.structure()]    #jm
        rows=[]
        for row in range(0, len(self._cursor)):
            currentRow=[]
            for column in columnNames:
                currentRow.append(getattr(self._cursor[row], column))
            rows.append(currentRow)
        return rows

if __name__ == '__main__':
    # We are in an interactive session so run our test routines
    # Connect to the database
    ##connection={ 'databasename':'andy'
    ##            ,'directory':'E:\Gadfly'}
    connection={'databasename':'calflora.db', 'directory':'.'}
    dbHolder = browse(connection)
    # Return all of our table names into user_tables
    user_tables = dbHolder.getTables()

    # Print out the structure of each table and its first row
    print "--------------------------------------------------"
    for table in user_tables:
        print "table:", table
        print dbHolder.getQueryString(table)
        print dbHolder.getRow(table)
        print "--------------------------------------------------"

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