Geografic-Information-System/scripts/v.db.dropcolumn/v.db.dropcolumn.py

#!/usr/bin/env python3

############################################################################
#
# MODULE:       v.db.dropcolumn
# AUTHOR(S):    Markus Neteler
#               Converted to Python by Glynn Clements
# PURPOSE:      interface to db.execute to drop a column from the
#               attribute table connected to a given vector map
#               - Based on v.db.addcolumn
#               - with special trick for SQLite
# COPYRIGHT:    (C) 2007 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.
#
#############################################################################


# %module
# % description: Drops a column from the attribute table connected to a given vector map.
# % keyword: vector
# % keyword: attribute table
# % keyword: database
# %end

# %option G_OPT_V_MAP
# % key: map
# %end

# %option G_OPT_V_FIELD
# %end

# %option G_OPT_DB_COLUMNS
# % description: Name of attribute column(s) to drop
# % required: yes
# %end

import string
import grass.script as grass
from grass.exceptions import CalledModuleError


def main():
    map = options["map"]
    layer = options["layer"]
    columns = options["columns"].split(",")

    mapset = grass.gisenv()["MAPSET"]

    # does map exist in CURRENT mapset?
    if not grass.find_file(map, element="vector", mapset=mapset)["file"]:
        grass.fatal(_("Vector map <%s> not found in current mapset") % map)

    f = grass.vector_layer_db(map, layer)

    table = f["table"]
    keycol = f["key"]
    database = f["database"]
    driver = f["driver"]

    if not table:
        grass.fatal(
            _(
                "There is no table connected to the input vector map. "
                "Unable to delete any column. Exiting."
            )
        )

    if keycol in columns:
        grass.fatal(
            _(
                "Unable to delete <%s> column as it is needed to keep table <%s> "
                "connected to the input vector map <%s>"
            )
            % (keycol, table, map)
        )

    for column in columns:
        if column not in grass.vector_columns(map, layer):
            grass.warning(
                _("Column <%s> not found in table <%s>. Skipped") % (column, table)
            )
            continue

        if driver == "sqlite":
            # echo "Using special trick for SQLite"
            # http://www.sqlite.org/faq.html#q11
            colnames = []
            coltypes = []
            for f in grass.db_describe(table, database=database, driver=driver)["cols"]:
                if f[0] == column:
                    continue
                colnames.append(f[0])
                # see db_sqltype_name() for type names
                if f[1] == "CHARACTER":
                    # preserve field length for sql type "CHARACTER"
                    coltypes.append("%s %s(%s)" % (f[0], f[1], f[2]))
                else:
                    coltypes.append("%s %s" % (f[0], f[1]))

            colnames = ", ".join(colnames)
            coltypes = ", ".join(coltypes)

            cmds = [
                "BEGIN TRANSACTION",
                "CREATE TEMPORARY TABLE ${table}_backup (${coldef})",
                "INSERT INTO ${table}_backup SELECT ${colnames} FROM ${table}",
                "DROP TABLE ${table}",
                "CREATE TABLE ${table}(${coldef})",
                "INSERT INTO ${table} SELECT ${colnames} FROM ${table}_backup",
                "CREATE UNIQUE INDEX ${table}_cat ON ${table} (${keycol} )",
                "DROP TABLE ${table}_backup",
                "COMMIT",
            ]
            tmpl = string.Template(";\n".join(cmds))
            sql = tmpl.substitute(
                table=table, coldef=coltypes, colnames=colnames, keycol=keycol
            )
        else:
            sql = "ALTER TABLE %s DROP COLUMN %s" % (table, column)

        try:
            grass.write_command(
                "db.execute", input="-", database=database, driver=driver, stdin=sql
            )
        except CalledModuleError:
            grass.fatal(_("Deleting column failed"))

    # write cmd history:
    grass.vector_history(map)


if __name__ == "__main__":
    options, flags = grass.parser()
    main()