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gadflyBrowse.py

#!/usr/bin/python

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

"""
Module Name: gadflyBrowse
Description: Plug in for PythonCard application dbBrowse to provide Gadfly 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.
"""

import gadfly

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=['__TABLE_NAMES__', '__INDEXCOLS__', '__COLUMNS__', '__INDICES__', '__DATADEFS__', 'DUAL']
        try:
            # Not providing a db name is guaranteed to ruin our connection
            if not connection['databasename']:
                raise ValueError
            self._db = gadfly.gadfly( databasename=connection['databasename']
                                     ,directory=connection['directory'] )
            self._cursor=self._db.cursor()
            # This one is used in getRow
            self._tableName=''
        except:
            self._cursor=None
            self._tableName=None

    def getTables(self):
        "Return a list of all of the non-system tables in <database>"
        stmt = "SELECT table_name FROM __table_names__"
        self._cursor.execute(stmt)
        # I'm using a list comprehension here instead of a for loop,
        # either will do but I think this is more concise (unlike this comment)
        return [ x[0] for x in self._cursor.fetchall() if x[0] not in self._system_tables ]

    def getColumns(self, tableName):
        "Get the definition of the columns in tableName"
        stmt = "SELECT column_name FROM __columns__ WHERE table_name = ?" 
        self._cursor.execute(stmt, (tableName,))
        # format of Gadfly definitions is;
        #  column name
        # format of dbBrowser column definitions is
        #  column name, data type, length (for display), nullable, key, default
        columnDefs = []
        for column in self._cursor.fetchall():
            columnName = column[0]
            dataType, nullable, key, default  = "varchar", "", "", ""
            # Dodgy default, but if works for me
            precision = 255
            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.execute(self.getQueryString(tableName))
        try:
            result = self._cursor.fetchone()
        except gadfly.database.error:
            result = None
        return result

    def getRows(self, tableName):
        "Get all of the rows from tableName"
        if tableName!=self._tableName:
            self._tableName=tableName
        self._cursor.execute(self.getQueryString(tableName))
        try:
            result = self._cursor.fetchall()
        except gadfly.database.error:
            result = None
        return result

if __name__ == '__main__':
    # We are in an interactive session so run our test routines
    # Connect to the database
    connection={ 'databasename':'andy'
                ,'directory':'E:\Gadfly'}
    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 dbHolder.getQueryString(table)
        print dbHolder.getRow(table)
        print "--------------------------------------------------"

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