Geografic-Information-System/lib/python/script/db.py

"""
Database related functions to be used in Python scripts.

Usage:

::

    from grass.script import db as grass

    grass.db_describe(table)
    ...

(C) 2008-2015 by the GRASS Development Team
This program is free software under the GNU General Public
License (>=v2). Read the file COPYING that comes with GRASS
for details.

.. sectionauthor:: Glynn Clements
.. sectionauthor:: Martin Landa <landa.martin gmail.com>
"""
from __future__ import absolute_import
from .core import *
from .utils import try_remove
from grass.exceptions import CalledModuleError


def db_describe(table, **args):
    """Return the list of columns for a database table
    (interface to `db.describe -c`). Example:

    >>> run_command('g.copy', vector='firestations,myfirestations')
    0
    >>> db_describe('myfirestations') # doctest: +ELLIPSIS
    {'nrows': 71, 'cols': [['cat', 'INTEGER', '20'], ... 'ncols': 22}
    >>> run_command('g.remove', flags='f', type='vector', name='myfirestations')
    0

    :param str table: table name
    :param list args:

    :return: parsed module output
    """
    s = read_command('db.describe', flags='c', table=table, **args)
    if not s:
        fatal(_("Unable to describe table <%s>") % table)

    cols = []
    result = {}
    for l in s.splitlines():
        f = l.split(':')
        key = f[0]
        f[1] = f[1].lstrip(' ')
        if key.startswith('Column '):
            n = int(key.split(' ')[1])
            cols.insert(n, f[1:])
        elif key in ['ncols', 'nrows']:
            result[key] = int(f[1])
        else:
            result[key] = f[1:]
    result['cols'] = cols

    return result


def db_table_exist(table, **args):
    """Check if table exists.

    If no driver or database are given, then default settings is used
    (check db_connection()).

    >>> run_command('g.copy', vector='firestations,myfirestations')
    0
    >>> db_table_exist('myfirestations')
    True
    >>> run_command('g.remove', flags='f', type='vector', name='myfirestations')
    0

    :param str table: table name
    :param args:

    :return: True for success, False otherwise
    """
    nuldev = file(os.devnull, 'w+')
    ok = True
    try:
        run_command('db.describe', flags='c', table=table,
                    stdout=nuldev, stderr=nuldev, **args)
    except CalledModuleError:
        ok = False
    finally:
        nuldev.close()

    return ok


def db_connection(force=False):
    """Return the current database connection parameters
    (interface to `db.connect -g`). Example:

    >>> db_connection()
    {'group': '', 'schema': '', 'driver': 'sqlite', 'database': '$GISDBASE/$LOCATION_NAME/$MAPSET/sqlite/sqlite.db'}

    :param force True to set up default DB connection if not defined

    :return: parsed output of db.connect
    """
    try:
        nuldev = file(os.devnull, 'w')
        conn = parse_command('db.connect', flags='g', stderr=nuldev)
        nuldev.close()
    except CalledModuleError:
        conn = None
    
    if not conn and force:
        run_command('db.connect', flags='c')
        conn = parse_command('db.connect', flags='g')

    return conn

def db_select(sql=None, filename=None, table=None, **args):
    """Perform SQL select statement

    Note: one of <em>sql</em>, <em>filename</em>, or <em>table</em>
    arguments must be provided.

    Examples:

    >>> run_command('g.copy', vector='firestations,myfirestations')
    0
    >>> db_select(sql = 'SELECT cat,CITY FROM myfirestations WHERE cat < 4')
    (('1', 'Morrisville'), ('2', 'Morrisville'), ('3', 'Apex'))

    Simplyfied usage (it performs <tt>SELECT * FROM myfirestations</tt>.)

    >>> db_select(table = 'myfirestations') # doctest: +ELLIPSIS
    (('1', '24', 'Morrisville #3', ... 'HS2A', '1.37'))
    >>> run_command('g.remove', flags='f', type='vector', name='myfirestations')
    0

    :param str sql: SQL statement to perform (or None)
    :param str filename: name of file with SQL statements (or None)
    :param str table: name of table to query (or None)
    :param str args:  see \gmod{db.select} arguments
    """
    fname = tempfile(create=False)
    if sql:
        args['sql'] = sql
    elif filename:
        args['input'] = filename
    elif table:
        args['table'] = table
    else:
        fatal(_("Programmer error: '%(sql)s', '%(filename)s', or '%(table)s' must be provided") %
              {'sql': 'sql', 'filename': 'filename', 'table': 'table'} )

    if 'sep' not in args:
        args['sep'] = '|'

    try:
        run_command('db.select', quiet=True, flags='c',
                    output=fname, **args)
    except CalledModuleError:
        fatal(_("Fetching data failed"))

    ofile = open(fname)
    result = [tuple(x.rstrip(os.linesep).split(args['sep'])) for x in ofile.readlines()]
    ofile.close()
    try_remove(fname)

    return tuple(result)


def db_table_in_vector(table):
    """Return the name of vector connected to the table.
    It returns None if no vectors are connected to the table.

    >>> run_command('g.copy', vector='firestations,myfirestations')
    0
    >>> db_table_in_vector('myfirestations')
    ['myfirestations@user1']
    >>> db_table_in_vector('mfirestations')
    >>> run_command('g.remove', flags='f', type='vector', name='myfirestations')
    0

    :param str table: name of table to query
    """
    from .vector import vector_db
    nuldev = file(os.devnull, 'w')
    used = []
    vects = list_strings('vect')
    for vect in vects:
        for f in vector_db(vect, stderr=nuldev).values():
            if not f:
                continue
            if f['table'] == table:
                used.append(vect)
                break
    if len(used) > 0:
        return used
    else:
        return None

def db_begin_transaction(driver):
    """Begin transaction.

    :return: SQL command as string
    """
    if driver in ('sqlite', 'pg'):
        return 'BEGIN'
    if driver == 'mysql':
        return 'START TRANSACTION'
    return ''

def db_commit_transaction(driver):
    """Commit transaction.

    :return: SQL command as string
    """
    if driver in ('sqlite', 'pg', 'mysql'):
        return 'COMMIT'
    return ''