lsst.dax.apdb.cassandra.apdbMetadataCassandra.ApdbMetadataCassandra Class Reference

Inheritance diagram for lsst.dax.apdb.cassandra.apdbMetadataCassandra.ApdbMetadataCassandra:

Public Member Functions
	__init__ (self, Any session, str table_name, str keyspace, str read_profile, str write_profile)
str|None	get (self, str key, str|None default=None)
None	set (self, str key, str value, *bool force=False)
bool	delete (self, str key)
Generator[tuple[str, str], None, None]	items (self)
bool	empty (self)
bool	table_exists (self)

Protected Attributes
	_session
	_read_profile
	_write_profile
	_part
	_preparer
	_table_clause

Detailed Description

Implementation of `ApdbMetadata` for Cassandra backend.

Parameters
----------
session : `cassandra.cluster.Session`
    Cassandra session instance.
schema : `ApdbSqlSchema`
    Object providing access to schema details.

Definition at line 33 of file apdbMetadataCassandra.py.

Constructor & Destructor Documentation

__init__()

lsst.dax.apdb.cassandra.apdbMetadataCassandra.ApdbMetadataCassandra.__init__	(		self,
		Any	session,
		str	table_name,
		str	keyspace,
		str	read_profile,
		str	write_profile )

Definition at line 44 of file apdbMetadataCassandra.py.

    def __init__(self, session: Any, table_name: str, keyspace: str, read_profile: str, write_profile: str):
        self._session = session
        self._read_profile = read_profile
        self._write_profile = write_profile
        self._part = 0  # Partition for all rows
        self._preparer = PreparedStatementCache(session)
        # _table_clause will be None when metadata table is not configured
        self._table_clause: str | None = None
 
        query = "SELECT count(*) FROM system_schema.tables WHERE keyspace_name = %s and table_name = %s"
        result = self._session.execute(query, (keyspace, table_name), execution_profile=read_profile)
        exists = bool(result.one()[0])
        if exists:
            self._table_clause = f"{quote_id(keyspace)}.{quote_id(table_name)}"
 

Member Function Documentation

delete()

bool lsst.dax.apdb.cassandra.apdbMetadataCassandra.ApdbMetadataCassandra.delete	(		self,
		str	key )

Delete metadata record.

Parameters
----------
key : `str`
    Metadata key, arbitrary non-empty string.

Returns
-------
existed : `bool`
    `True` is returned if attribute existed before it was deleted.

Reimplemented from lsst.dax.apdb.apdbMetadata.ApdbMetadata.

Definition at line 86 of file apdbMetadataCassandra.py.

    def delete(self, key: str) -> bool:
        # Docstring is inherited.
        if self._table_clause is None:
            # Missing table means nothing to delete.
            return False
        if not key:
            raise ValueError("name cannot be empty")
        query = f"DELETE FROM {self._table_clause} WHERE meta_part = ? AND name = ?"
        # Cassandra cannot tell how many rows are deleted, just check if row
        # exists now.
        exists = self.get(key) is not None
        # Race is still possible between check and remove.
        self._session.execute(
            self._preparer.prepare(query), (self._part, key), execution_profile=self._write_profile
        )
        return exists
 

empty()

bool lsst.dax.apdb.cassandra.apdbMetadataCassandra.ApdbMetadataCassandra.empty

(

self

)

Check whether attributes set is empty.

Returns
-------
empty : `bool`
    `True` if there are no any attributes defined. `True` is also
    returned if metadata table is missing.

Reimplemented from lsst.dax.apdb.apdbMetadata.ApdbMetadata.

Definition at line 115 of file apdbMetadataCassandra.py.

    def empty(self) -> bool:
        # Docstring is inherited.
        if self._table_clause is None:
            # Missing table means empty.
            return True
        query = f"SELECT count(*) FROM {self._table_clause} WHERE meta_part = ?"
        result = self._session.execute(
            self._preparer.prepare(query), (self._part,), execution_profile=self._read_profile
        )
        row = result.one()
        return row[0] == 0
 

get()

str | None lsst.dax.apdb.cassandra.apdbMetadataCassandra.ApdbMetadataCassandra.get	(		self,
		str	key,
		str | None	default = None )

Retrieve value of a given metadata record.

Parameters
----------
key : `str`
    Metadata key, arbitrary non-empty string.
default : `str`, optional
    Default value returned when key does not exist, can be string
    or `None`.

Returns
-------
value : `str` or `None`
    Metadata value, if key does not exist then ``default`` is returned.

Reimplemented from lsst.dax.apdb.apdbMetadata.ApdbMetadata.

Definition at line 59 of file apdbMetadataCassandra.py.

    def get(self, key: str, default: str | None = None) -> str | None:
        # Docstring is inherited.
        if self._table_clause is None:
            return default
        query = f"SELECT value FROM {self._table_clause} WHERE meta_part = ? AND name = ?"
        result = self._session.execute(
            self._preparer.prepare(query), (self._part, key), execution_profile=self._read_profile
        )
        if (row := result.one()) is not None:
            return row[0]
        else:
            return default
 

items()

Generator[tuple[str, str], None, None] lsst.dax.apdb.cassandra.apdbMetadataCassandra.ApdbMetadataCassandra.items

(

self

)

Iterate over records and yield their keys and values.

Yields
------
key : `str`
    Metadata key.
value : `str`
    Corresponding metadata value.

Reimplemented from lsst.dax.apdb.apdbMetadata.ApdbMetadata.

Definition at line 103 of file apdbMetadataCassandra.py.

    def items(self) -> Generator[tuple[str, str], None, None]:
        # Docstring is inherited.
        if self._table_clause is None:
            # Missing table means nothing to return.
            return
        query = f"SELECT name, value FROM {self._table_clause} WHERE meta_part = ?"
        result = self._session.execute(
            self._preparer.prepare(query), (self._part,), execution_profile=self._read_profile
        )
        for row in result:
            yield tuple(row)
 

set()

None lsst.dax.apdb.cassandra.apdbMetadataCassandra.ApdbMetadataCassandra.set	(		self,
		str	key,
		str	value,
		*bool	force = False )

Set value for a given metadata record.

Parameters
----------
key : `str`
    Metadata key, arbitrary non-empty string.
value : `str`
    New metadata value, an arbitrary string. Due to deficiencies of
    some database engines we are not allowing empty strings to be
    stored in the database, and ``value`` cannot be an empty string.
force : `bool`, optional
    Controls handling of existing metadata. With default `False`
    value an exception is raised if ``key`` already exists, if `True`
    is passed then value of the existing key will be updated.

Raises
------
KeyError
    Raised if key already exists but ``force`` option is false.
ValueError
    Raised if key or value parameters are empty.

Reimplemented from lsst.dax.apdb.apdbMetadata.ApdbMetadata.

Definition at line 72 of file apdbMetadataCassandra.py.

    def set(self, key: str, value: str, *, force: bool = False) -> None:
        # Docstring is inherited.
        if self._table_clause is None:
            raise RuntimeError("Metadata table does not exist")
        if not key or not value:
            raise ValueError("name and value cannot be empty")
        query = f"INSERT INTO {self._table_clause} (meta_part, name, value) VALUES (?, ?, ?)"
        if not force and self.get(key) is not None:
            raise KeyError(f"Metadata key {key!r} already exists")
        # Race is still possible between check and insert.
        self._session.execute(
            self._preparer.prepare(query), (self._part, key, value), execution_profile=self._write_profile
        )
 

table_exists()

bool lsst.dax.apdb.cassandra.apdbMetadataCassandra.ApdbMetadataCassandra.table_exists

(

self

)

Return `True` if metadata table exists.

Definition at line 127 of file apdbMetadataCassandra.py.

    def table_exists(self) -> bool:
        """Return `True` if metadata table exists."""
        return self._table_clause is not None

Member Data Documentation

_part

lsst.dax.apdb.cassandra.apdbMetadataCassandra.ApdbMetadataCassandra._part

protected

Definition at line 48 of file apdbMetadataCassandra.py.

_preparer

lsst.dax.apdb.cassandra.apdbMetadataCassandra.ApdbMetadataCassandra._preparer

protected

Definition at line 49 of file apdbMetadataCassandra.py.

_read_profile

lsst.dax.apdb.cassandra.apdbMetadataCassandra.ApdbMetadataCassandra._read_profile

protected

Definition at line 46 of file apdbMetadataCassandra.py.

_session

lsst.dax.apdb.cassandra.apdbMetadataCassandra.ApdbMetadataCassandra._session

protected

Definition at line 45 of file apdbMetadataCassandra.py.

_table_clause

lsst.dax.apdb.cassandra.apdbMetadataCassandra.ApdbMetadataCassandra._table_clause

protected

Definition at line 57 of file apdbMetadataCassandra.py.

_write_profile

lsst.dax.apdb.cassandra.apdbMetadataCassandra.ApdbMetadataCassandra._write_profile

protected

Definition at line 47 of file apdbMetadataCassandra.py.

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The documentation for this class was generated from the following file:

• /j/snowflake/release/lsstsw/stack/lsst-scipipe-8.0.0/Linux64/dax_apdb/g88963caddf+0cb8e002cc/python/lsst/dax/apdb/cassandra/apdbMetadataCassandra.py