idDealer.py

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import coral
import nameDealer
class idDealer(object):
    """Manages the autoincremental ID values.\n
    Input: coral.schema object
    """
    def __init__( self , schema  ):
        self.__schema = schema
        self.__idTableColumnName = nameDealer.idTableColumnDefinition()[0]
        self.__idTableColumnType = nameDealer.idTableColumnDefinition()[1]
        
    def getIDColumnDefinition( self ):
        return (self.__idTableColumnName, self.__idTableColumnType)
    
    def getIDforTable( self, tableName ):
        """
        get the new id value to use for the given table
        """
        try:
            idtableName = nameDealer.idTableName(tableName)
            query = self.__schema.tableHandle(idtableName).newQuery()
            query.addToOutputList(self.__idTableColumnName)
            query.setForUpdate() #lock it
            cursor = query.execute()
            result = 0
            while ( next(cursor) ):
                result = cursor.currentRow()[self.__idTableColumnName].data()
            del query
            return result
        except Exception as e:
            raise Exception(str(e))

    def generateNextIDForTable( self, tableName ):
        """
        Set the nextID in the IDTableName to current id value + 1 .\n
        Input: ID table name.
        """
        try:
            idtableName = nameDealer.idTableName(tableName)
            tableHandle = self.__schema.tableHandle(idtableName)
            query = tableHandle.newQuery()
            query.addToOutputList(self.__idTableColumnName)
            query.setForUpdate() #lock it
            cursor = query.execute()
            result = 0
            while ( next(cursor) ):
                result = cursor.currentRow()[0].data()
            dataEditor = tableHandle.dataEditor()
            inputData = coral.AttributeList()
            dataEditor.updateRows('NEXTID = NEXTID+1','',inputData)
            del query            
            return result+1
        except Exception as e:
            raise Exception(str(e))

if __name__ == "__main__":
    fakeIDtableName='Fake_ID'
    svc=coral.ConnectionService()
    session=svc.connect('sqlite_file:fake.db')
    transaction=session.transaction()
    try:
        transaction.start(False)
        schema=session.nominalSchema()
        idor=idDealer(schema)
        if schema.existsTable(fakeIDtableName) is False:
          description=coral.TableDescription()
          description.setName(fakeIDtableName)
          description.setPrimaryKey(idor.getIDColumnDefinition()[0])        
          description.insertColumn(idor.getIDColumnDefinition()[0],idor.getIDColumnDefinition()[1])
          idtableHandle=schema.createTable(description)
          idtableHandle.privilegeManager().grantToPublic(coral.privilege_Select)
          inputData=coral.AttributeList()
          editor=idtableHandle.dataEditor()
          editor.rowBuffer(inputData)
          inputData[ idor.getIDColumnDefinition()[0] ].setData(0)
          editor.insertRow(inputData)
        idor.generateNextIDForTable('Fake')
        print idor.getIDforTable('Fake')
        transaction.commit()
        del session
    except coral.Exception as e:
        transaction.rollback()
        del session
    except Exception as e:
        print 'failed in unit test'
        print str(e)
        del session