Add util/dbutil.py: open/create/update sqlite databases given some schema.

Author: Brian Warner <warner@lothar.com>
Signed-off-by: Daira Hopwood <daira@jacaranda.org>

src/allmydata/util/dbutil.py

@@ -0,0 +1,66 @@
+
+import os, sys
+
+import sqlite3
+from sqlite3 import IntegrityError
+[IntegrityError]
+
+
+class DBError(Exception):
+    pass
+
+
+def get_db(dbfile, stderr=sys.stderr,
+           create_version=(None, None), updaters={}, just_create=False, dbname="db",
+           journal_mode=None, synchronous=None):
+    """Open or create the given db file. The parent directory must exist.
+    create_version=(SCHEMA, VERNUM), and SCHEMA must have a 'version' table.
+    Updaters is a {newver: commands} mapping, where e.g. updaters[2] is used
+    to get from ver=1 to ver=2. Returns a (sqlite3,db) tuple, or raises
+    DBError.
+    """
+    must_create = not os.path.exists(dbfile)
+    try:
+        db = sqlite3.connect(dbfile)
+    except (EnvironmentError, sqlite3.OperationalError), e:
+        raise DBError("Unable to create/open %s file %s: %s" % (dbname, dbfile, e))
+
+    schema, target_version = create_version
+    c = db.cursor()
+
+    # Enabling foreign keys allows stricter integrity checking.
+    # The default is unspecified according to <http://www.sqlite.org/foreignkeys.html#fk_enable>.
+    c.execute("PRAGMA foreign_keys = ON;")
+
+    if journal_mode is not None:
+        c.execute("PRAGMA journal_mode = %s;" % (journal_mode,))
+
+    if synchronous is not None:
+        c.execute("PRAGMA synchronous = %s;" % (synchronous,))
+
+    if must_create:
+        c.executescript(schema)
+        c.execute("INSERT INTO version (version) VALUES (?)", (target_version,))
+        db.commit()
+
+    try:
+        c.execute("SELECT version FROM version")
+        version = c.fetchone()[0]
+    except sqlite3.DatabaseError, e:
+        # this indicates that the file is not a compatible database format.
+        # Perhaps it was created with an old version, or it might be junk.
+        raise DBError("%s file is unusable: %s" % (dbname, e))
+
+    if just_create: # for tests
+        return (sqlite3, db)
+
+    while version < target_version and version+1 in updaters:
+        c.executescript(updaters[version+1])
+        db.commit()
+        version = version+1
+    if version != target_version:
+        raise DBError("Unable to handle %s version %s" % (dbname, version))
+
+    return (sqlite3, db)
+
+