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

"""!@package grass.script.db

@brief GRASS Python scripting module (database functions)

Database related functions to be used in Python scripts.

Usage:

@code
from grass.script import db as grass

grass.db_describe(table)
...
@endcode

(C) 2008-2009 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.

@author Glynn Clements
@author Martin Landa <landa.martin gmail.com>
"""

import tempfile as pytempfile # conflict with core.tempfile

from core import *

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

    \code
    >>> grass.db_describe('lakes')
    {'nrows': 15279, 'cols': [['cat', 'INTEGER', '11'], ['AREA', 'DOUBLE PRECISION', '20'],
    ['PERIMETER', 'DOUBLE PRECISION', '20'], ['FULL_HYDRO', 'DOUBLE PRECISION', '20'],
    ['FULL_HYDR2', 'DOUBLE PRECISION', '20'], ['FTYPE', 'CHARACTER', '24'],
    ['FCODE', 'INTEGER', '11'], ['NAME', 'CHARACTER', '99']], 'ncols': 8}
    \endcode

    @param table table name
    @param 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

# run "db.connect -p" and parse output

def db_table_exist(table, **args):
    """!Return True if database table exists, False otherwise

    @param table table name
    @param args

    @return True for success, False otherwise
    """
    result = run_command('db.describe', flags = 'c', table = table, **args)
    if result == 0:
	    return True
    else:
	    return False

def db_connection():
    """!Return the current database connection parameters
    (interface to `db.connect -p'). Example:

    \code
    >>> grass.db_connection()
    {'group': 'x', 'schema': '', 'driver': 'dbf', 'database': '$GISDBASE/$LOCATION_NAME/$MAPSET/dbf/'}
    \endcode

    @return parsed output of db.connect
    """
    s = read_command('db.connect', flags = 'p')
    return parse_key_val(s, sep = ':')

def db_select(table, sql, file = False, **args):
    """!Perform SQL select statement

    @param table table name
    @param sql   SQL select statement (string or file)
    @param file  True if sql is filename
    @param args  see db.select arguments
    """
    fname = tempfile(create = False)
    if not file:
        ret = run_command('db.select', quiet = True,
                          flags = 'c',
                          table = table,
                          sql = sql,
                          output = fname,
			  **args)
    else: # -> sql is file
        ret = run_command('db.select', quiet = True,
                          flags = 'c',
                          table = table,
                          input = sql,
                          output = fname,
			  **args)
    
    if ret != 0:
        fatal(_("Fetching data from table <%s> failed") % table)

    ofile = open(fname)
    result = map(lambda x: x.rstrip(os.linesep), ofile.readlines())
    ofile.close()
    try_remove(fname)
        
    return result