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apdbMetadataCassandra.py
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1# This file is part of dax_apdb.
2#
3# Developed for the LSST Data Management System.
4# This product includes software developed by the LSST Project
5# (http://www.lsst.org).
6# See the COPYRIGHT file at the top-level directory of this distribution
7# for details of code ownership.
8#
9# This program is free software: you can redistribute it and/or modify
10# it under the terms of the GNU General Public License as published by
11# the Free Software Foundation, either version 3 of the License, or
12# (at your option) any later version.
13#
14# This program is distributed in the hope that it will be useful,
15# but WITHOUT ANY WARRANTY; without even the implied warranty of
16# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17# GNU General Public License for more details.
18#
19# You should have received a copy of the GNU General Public License
20# along with this program. If not, see <http://www.gnu.org/licenses/>.
21
22from __future__ import annotations
23
24__all__ = ["ApdbMetadataCassandra"]
25
26from collections.abc import Generator
27from typing import Any
28
29from ..apdbMetadata import ApdbMetadata
30from .cassandra_utils import PreparedStatementCache, quote_id
31
32
34 """Implementation of `ApdbMetadata` for Cassandra backend.
35
36 Parameters
37 ----------
38 session : `cassandra.cluster.Session`
39 Cassandra session instance.
40 schema : `ApdbSqlSchema`
41 Object providing access to schema details.
42 """
43
44 def __init__(self, session: Any, table_name: str, keyspace: str, read_profile: str, write_profile: str):
45 self._session = session
46 self._read_profile = read_profile
47 self._write_profile = write_profile
48 self._part = 0 # Partition for all rows
50 # _table_clause will be None when metadata table is not configured
51 self._table_clause: str | None = None
52
53 query = "SELECT count(*) FROM system_schema.tables WHERE keyspace_name = %s and table_name = %s"
54 result = self._session.execute(query, (keyspace, table_name), execution_profile=read_profile)
55 exists = bool(result.one()[0])
56 if exists:
57 self._table_clause = f"{quote_id(keyspace)}.{quote_id(table_name)}"
58
59 def get(self, key: str, default: str | None = None) -> str | None:
60 # Docstring is inherited.
61 if self._table_clause is None:
62 return default
63 query = f"SELECT value FROM {self._table_clause} WHERE meta_part = ? AND name = ?"
64 result = self._session.execute(
65 self._preparer.prepare(query), (self._part, key), execution_profile=self._read_profile
66 )
67 if (row := result.one()) is not None:
68 return row[0]
69 else:
70 return default
71
72 def set(self, key: str, value: str, *, force: bool = False) -> None:
73 # Docstring is inherited.
74 if self._table_clause is None:
75 raise RuntimeError("Metadata table does not exist")
76 if not key or not value:
77 raise ValueError("name and value cannot be empty")
78 query = f"INSERT INTO {self._table_clause} (meta_part, name, value) VALUES (?, ?, ?)"
79 if not force and self.get(key) is not None:
80 raise KeyError(f"Metadata key {key!r} already exists")
81 # Race is still possible between check and insert.
82 self._session.execute(
83 self._preparer.prepare(query), (self._part, key, value), execution_profile=self._write_profile
84 )
85
86 def delete(self, key: str) -> bool:
87 # Docstring is inherited.
88 if self._table_clause is None:
89 # Missing table means nothing to delete.
90 return False
91 if not key:
92 raise ValueError("name cannot be empty")
93 query = f"DELETE FROM {self._table_clause} WHERE meta_part = ? AND name = ?"
94 # Cassandra cannot tell how many rows are deleted, just check if row
95 # exists now.
96 exists = self.get(key) is not None
97 # Race is still possible between check and remove.
98 self._session.execute(
99 self._preparer.prepare(query), (self._part, key), execution_profile=self._write_profile
100 )
101 return exists
102
103 def items(self) -> Generator[tuple[str, str], None, None]:
104 # Docstring is inherited.
105 if self._table_clause is None:
106 # Missing table means nothing to return.
107 return
108 query = f"SELECT name, value FROM {self._table_clause} WHERE meta_part = ?"
109 result = self._session.execute(
110 self._preparer.prepare(query), (self._part,), execution_profile=self._read_profile
111 )
112 for row in result:
113 yield tuple(row)
114
115 def empty(self) -> bool:
116 # Docstring is inherited.
117 if self._table_clause is None:
118 # Missing table means empty.
119 return True
120 query = f"SELECT count(*) FROM {self._table_clause} WHERE meta_part = ?"
121 result = self._session.execute(
122 self._preparer.prepare(query), (self._part,), execution_profile=self._read_profile
123 )
124 row = result.one()
125 return row[0] == 0
126
127 def table_exists(self) -> bool:
128 """Return `True` if metadata table exists."""
129 return self._table_clause is not None
str|None get(self, str key, str|None default=None)
None set(self, str key, str value, *, bool force=False)
__init__(self, Any session, str table_name, str keyspace, str read_profile, str write_profile)