~azzar1/unity/add-show-desktop-key

# IVLE - Informatics Virtual Learning Environment

# Copyright (C) 2007-2008 The University of Melbourne

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

#

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

# GNU General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

# Module: Database

# Author: Matt Giuca

# Date:   15/2/2008

# Code to talk to the PostgreSQL database.

# (This is the Data Access Layer).

# All DB code should be in this module to ensure portability if we want to

# change the DB implementation.

# This means no SQL strings should be outside of this module. Add functions

# here to perform the activities needed, and place the SQL code for those

# activities within.

# CAUTION to editors of this module.

# All string inputs must be sanitized by calling _escape before being

# formatted into an SQL query string.

import pg

import md5

import copy

import time

import ivle.conf

from ivle import caps

TIMESTAMP_FORMAT = '%Y-%m-%d %H:%M:%S'

def _escape(val):

    """Wrapper around pg.escape_string. Prepares the Python value for use in

    SQL. Returns a string, which may be safely placed verbatim into an SQL

    query.

    Handles the following types:

    * str: Escapes the string, and also quotes it.

    * int/long/float: Just converts to an unquoted string.

    * bool: Returns as "TRUE" or "FALSE", unquoted.

    * NoneType: Returns "NULL", unquoted.

    * common.caps.Role: Returns the role as a quoted, lowercase string.

    * time.struct_time: Returns the time as a quoted string for insertion into

        a TIMESTAMP column.

    Raises a DBException if val has an unsupported type.

    """

    # "E'" is postgres's way of making "escape" strings.

    # Such strings allow backslashes to escape things. Since escape_string

    # converts a single backslash into two backslashes, it needs to be fed

    # into E mode.

    # Ref: http://www.postgresql.org/docs/8.2/static/sql-syntax-lexical.html

    # WARNING: PostgreSQL-specific code

    if val is None:

        return "NULL"

    elif isinstance(val, str) or isinstance(val, unicode):

        return "E'" + pg.escape_string(val) + "'"

    elif isinstance(val, bool):

        return "TRUE" if val else "FALSE"

    elif isinstance(val, int) or isinstance(val, long) \

        or isinstance(val, float):

        return str(val)

    elif isinstance(val, caps.Role):

        return _escape(str(val))

    elif isinstance(val, time.struct_time):

        return _escape(time.strftime(TIMESTAMP_FORMAT, val))

    else:

        raise DBException("Attempt to insert an unsupported type "

            "into the database (%s)" % repr(type(val)))

class DBException(Exception):

    """A DBException is for bad conditions in the database or bad input to

    these methods. If Postgres throws an exception it does not get rebadged.

    This is only for additional exceptions."""

    pass

class DB:

    """An IVLE database object. This object provides an interface to

    interacting with the IVLE database without using any external SQL.

    Most methods of this class have an optional dry argument. If true, they

    will return the SQL query string and NOT actually execute it. (For

    debugging purposes).

    Methods may throw db.DBException, or any of the pg exceptions as well.

    (In general, be prepared to catch exceptions!)

    """

    def __init__(self):

        """Connects to the database and creates a DB object.

        Takes no parameters - gets all the DB info from the configuration."""

        self.open = False

        self.db = pg.connect(host=ivle.conf.db_host, port=ivle.conf.db_port,

                         dbname=ivle.conf.db_dbname,

                         user=ivle.conf.db_user, passwd=ivle.conf.db_password)

        self.open = True

    def __del__(self):

        if self.open:

            self.db.close()

    # GENERIC DB FUNCTIONS #

    @staticmethod

    def check_dict(dict, tablefields, disallowed=frozenset([]), must=False):

        """Checks that a dict does not contain keys that are not fields

        of the specified table.

        dict: A mapping from string keys to values; the keys are checked to

            see that they correspond to login table fields.

        tablefields: Collection of strings for field names in the table.

            Only these fields will be allowed.

        disallowed: Optional collection of strings for field names that are

            not allowed.

        must: If True, the dict MUST contain all fields in tablefields.

            If False, it may contain any subset of the fields.

        Returns True if the dict is valid, False otherwise.

        """

        allowed = frozenset(tablefields) - frozenset(disallowed)

        dictkeys = frozenset(dict.keys())

        if must:

            return allowed == dictkeys

        else:

            return allowed.issuperset(dictkeys)

    def insert(self, dict, tablename, tablefields, disallowed=frozenset([]),

        dry=False):

        """Inserts a new row in a table, using data from a supplied

        dictionary (which will be checked by check_dict).

        dict: Dictionary mapping column names to values. The values may be

            any of the following types:

            str, int, long, float, NoneType.

        tablename: String, name of the table to insert into. Will NOT be

            escaped - must be a valid identifier.

        tablefields, disallowed: see check_dict.

        dry: Returns the SQL query as a string, and does not execute it.

        Raises a DBException if the dictionary contains invalid fields.

        """

        if not DB.check_dict(dict, tablefields, disallowed):

            extras = set(dict.keys()) - tablefields

            raise DBException("Supplied dictionary contains invalid fields. (%s)" % (repr(extras)))

        # Build two lists concurrently: field names and values, as SQL strings

        fieldnames = []

        values = []

        for k,v in dict.items():

            fieldnames.append(k)

            values.append(_escape(v))

        if len(fieldnames) == 0: return

        fieldnames = ', '.join(fieldnames)

        values = ', '.join(values)

        query = ("INSERT INTO %s (%s) VALUES (%s);"

            % (tablename, fieldnames, values))

        if dry: return query

        self.db.query(query)

    def update(self, primarydict, updatedict, tablename, tablefields,

        primary_keys, disallowed_update=frozenset([]), dry=False):

        """Updates a row in a table, matching against primarydict to find the

        row, and using the data in updatedict (which will be checked by

        check_dict).

        primarydict: Dict mapping column names to values. The keys should be

            the table's primary key. Only rows which match this dict's values

            will be updated.

        updatedict: Dict mapping column names to values. The columns will be

            updated with the given values for the matched rows.

        tablename, tablefields, disallowed_update: See insert.

        primary_keys: Collection of strings which together form the primary

            key for this table. primarydict must contain all of these as keys,

            and only these keys.

        """

        if (not (DB.check_dict(primarydict, primary_keys, must=True)

            and DB.check_dict(updatedict, tablefields, disallowed_update))):

            raise DBException("Supplied dictionary contains invalid or missing fields (1).")

        # Make a list of SQL fragments of the form "field = 'new value'"

        # These fragments are ALREADY-ESCAPED

        setlist = []

        for k,v in updatedict.items():

            setlist.append("%s = %s" % (k, _escape(v)))

        wherelist = []

        for k,v in primarydict.items():

            wherelist.append("%s = %s" % (k, _escape(v)))

        if len(setlist) == 0 or len(wherelist) == 0:

            return

        # Join the fragments into a comma-separated string

        setstring = ', '.join(setlist)

        wherestring = ' AND '.join(wherelist)

        # Build the whole query as an UPDATE statement

        query = ("UPDATE %s SET %s WHERE %s;"

            % (tablename, setstring, wherestring))

        if dry: return query

        self.db.query(query)

    def get_single(self, primarydict, tablename, getfields, primary_keys,

        error_notfound="No rows found", dry=False):

        """Retrieves a single row from a table, returning it as a dictionary

        mapping field names to values. Matches against primarydict to find the

        row.

        primarydict, tablename, primary_keys: See update/delete.

        getfields: Collection of strings; the field names which will be

            returned as keys in the dictionary.

        error_notfound: Error message if 0 rows match.

        Raises a DBException if 0 rows match, with error_notfound as the msg.

        Raises an AssertError if >1 rows match (this should not happen if

            primary_keys is indeed the primary key).

        """

        if not DB.check_dict(primarydict, primary_keys, must=True):

            raise DBException("Supplied dictionary contains invalid or missing fields (3).")

        wherelist = []

        for k,v in primarydict.items():

            wherelist.append("%s = %s" % (k, _escape(v)))

        if len(getfields) == 0 or len(wherelist) == 0:

            return

        # Join the fragments into a comma-separated string

        getstring = ', '.join(getfields)

        wherestring = ' AND '.join(wherelist)

        # Build the whole query as an SELECT statement

        query = ("SELECT %s FROM %s WHERE %s;"

            % (getstring, tablename, wherestring))

        if dry: return query

        result = self.db.query(query)

        # Expecting exactly one

        if result.ntuples() != 1:

            # It should not be possible for ntuples to be greater than 1

            assert (result.ntuples() < 1)

            raise DBException(error_notfound)

        # Return as a dictionary

        return result.dictresult()[0]

    # PROBLEM AND PROBLEM ATTEMPT FUNCTIONS #

    def get_problem_problemid(self, exercisename, dry=False):

        """Given an exercise name, returns the associated problemID.

        If the exercise name is NOT in the database, it inserts it and returns

        the new problemID. Hence this may mutate the DB, but is idempotent.

        """

        try:

            d = self.get_single({"identifier": exercisename}, "problem",

                ['problemid'], frozenset(["identifier"]),

                dry=dry)

            if dry:

                return d        # Query string

        except DBException:

            if dry:

                # Shouldn't try again, must have failed for some other reason

                raise

            # if we failed to get a problemid, it was probably because

            # the exercise wasn't in the db. So lets insert it!

            #

            # The insert can fail if someone else simultaneously does

            # the insert, so if the insert fails, we ignore the problem. 

            try:

                self.insert({'identifier': exercisename}, "problem",

                        frozenset(['identifier']))

            except Exception, e:

                pass

            # Assuming the insert succeeded, we should be able to get the

            # problemid now.

            d = self.get_single({"identifier": exercisename}, "problem",

                ['problemid'], frozenset(["identifier"]))

        return d['problemid']

    def write_problem_save(self, user, exercisename, date, text, dry=False):

        """Writes text to the problem_save table (for when the user saves an

        exercise). Creates a new row, or overwrites an existing one if the

        user has already saved that problem.

        (Unlike problem_attempt, does not keep historical records).

        """

        problemid = self.get_problem_problemid(exercisename)

        try:

            return self.insert({

                    'problemid': problemid,

                    'loginid': user.id,

                    'date': date,

                    'text': text,

                }, 'problem_save',

                frozenset(['problemid','loginid','date','text']),

                dry=dry)

        except pg.ProgrammingError:

            # May have failed because this problemid/loginid row already

            # exists (they have a unique key constraint).

            # Do an update instead.

            if dry:

                # Shouldn't try again, must have failed for some other reason

                raise

            self.update({

                    'problemid': problemid,

                    'loginid': user.id,

                },

                {

                    'date': date,

                    'text': text,

                }, "problem_save",

                frozenset(['date', 'text']),

                frozenset(['problemid', 'loginid']))

    def close(self):

        """Close the DB connection. Do not call any other functions after

        this. (The behaviour of doing so is undefined).

        """

        self.db.close()

        self.open = False