grass.script.db — GRASS Python Library documentation

# Source code for grass.script.db

    """
    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>
    """

    import os
    from .core import (
        run_command,
        parse_command,
        read_command,
        tempfile,
        fatal,
        list_strings,
    )
    from .utils import try_remove
    from grass.exceptions import CalledModuleError

    def db_describe(table, env=None, **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:
        :param env: environment

        :return: parsed module output
        """
        if "database" in args and args["database"] == "":
            args.pop("database")
        if "driver" in args and args["driver"] == "":
            args.pop("driver")
        s = read_command("db.describe", flags="c", table=table, env=env, **args)
        if not s:
            fatal(_("Unable to describe table <%s>") % table)

        cols = []
        result = {}
        for line in s.splitlines():
            f = line.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, env=None, **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:
        :param env: environment

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

        return ok

    def db_connection(force=False, env=None):
        """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
        :param env: environment

        :return: parsed output of db.connect
        """  # noqa: E501
        try:
            nuldev = open(os.devnull, "w")
            conn = parse_command("db.connect", flags="g", stderr=nuldev, env=env)
            nuldev.close()
        except CalledModuleError:
            conn = None

        if not conn and force:
            run_command("db.connect", flags="c", env=env)
            conn = parse_command("db.connect", flags="g", env=env)

        return conn

    def db_select(sql=None, filename=None, table=None, env=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 *db.select* arguments
        :param env: environment
        """
        fname = tempfile(create=False, env=env)
        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, env=env, **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, mapset=".", env=None):
        """Return the name of vector connected to the table.
        By default it check only in the current mapset, because the same table
        name could be used also in other mapset by other vector.
        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
        :param env: environment
        """
        from .vector import vector_db

        nuldev = open(os.devnull, "w")
        used = []
        vects = list_strings("vector", mapset=mapset, env=env)
        for vect in vects:
            for f in vector_db(vect, stderr=nuldev, env=env).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 ""

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