Native gui: ongoing work, cables and fuses

yms/database.py

@@ -1,6 +1,7 @@
 import MySQLdb
+import secrets
 
-class Database():
+class Database:
 
     def __init__(self, hostname, dbname):
         self.hostname = hostname
@@ -48,6 +49,10 @@ class Database():
     def is_connected(self):
         return self.conn.open
 
+    def get_timestamp(self):
+        self.cur.execute("SELECT CURRENT_TIMESTAMP")
+        return self.cur.fetchone()[0]
+
     def last_error(self):
         if not self.error:
             return(0, '')
@@ -56,6 +61,70 @@ class Database():
         self.error = None
         return(code, text)
 
+    def load_enum(self, table, column):
+        """
+        TODO this is only an example! perhaps other keys needed
+        Load an enum directly from a database table and provide it as a
+        dictionary for use in, for example, selection lists.
+        """
+        sql = (
+            "SELECT TRIM(TRAILING ')' FROM SUBSTRING(column_type,6)) "
+            "FROM information_schema.columns "
+            "WHERE table_schema=DATABASE() AND table_name=%s AND column_name=%s AND data_type='enum'"
+            )
+        self.cur.execute(sql, (table, column))
+        row = self.cur.fetchone()
+        if not row:
+            return {}
+        return {
+            i: _(value.strip("'"))
+            for i, value in enumerate(row[0].split(','), 1)
+        }
+
+    def lock_acquire(self, table, key, userid):
+        token = secrets.token_hex(8)
+        # first try new lock
+        sql = (
+            "INSERT INTO recordlock (lock_table, lock_key, token, userid)"
+            "VALUES (%s, %s, %s, %s)"
+            )
+        try:
+            self.cur.execute(sql, (table, key, token, userid))
+            self.conn.commit()
+            return token
+        except self.conn.IntegrityError as e:
+            self.conn.rollback()
+            if e.errno != 1062:
+                raise
+        # lazy locking: lock exists but is old, so we use it
+        sql = (
+            "UPDATE recordlock "
+            "SET token=%s, userid=%s,"
+            "    created_at=CURRENT_TIMESTAMP, last_seen=CURRENT_TIMESTAMP "
+            "WHERE lock_table=%s AND lock_key=%s AND last_seen<CURRENT_TIMESTAMP-INTERVAL 5 MINUTE"
+            )
+        self.cur.execute(sql, (token, userid, table, key))
+        self.conn.commit()
+        if self.cur.rowcount == 1:
+            return token
+        return None
+
+    def lock_refresh(self, token):
+        sql = (
+            "UPDATE recordlock "
+            "SET last_seen=current_timestamp() "
+            "WHERE token=%s"
+            )
+        self.cur.execute(sql, (token,))
+        self.conn.commit()
+        return self.cur.rowcount == 1
+
+    def lock_release(self, token):
+        sql = "DELETE FROM recordlock WHERE token=%s"
+        self.cur.execute(sql, (token,))
+        self.conn.commit()
+        return self.cur.rowcount == 1
+
     def execute_write(self, sql, values=(), expected_rows=None):
         """
         Execute an INSERT, UPDATE, or DELETE statement.