sage.database.postgres_backends.postgres package

Submodules

sage.database.postgres_backends.postgres.connector module

class sage.database.postgres_backends.postgres.connector.DefaultPostgresConnector(table_name: str, dbname: str, user: str, password: str, host: str = '', port: int = 5432, fetch_size: int = 500)

Bases: sage.database.postgres_backends.connector.PostgresConnector

A DefaultPostgresConnector search for RDF triples in a PostgreSQL database.

Args:

  • table_name: Name of the SQL table containing RDF data.

  • dbname: the database name.

  • user: user name used to authenticate.

  • password: password used to authenticate.

  • host: database host address (defaults to UNIX socket if not provided).

  • port: connection port number (defaults to 5432 if not provided).

  • fetch_size: The number of SQL rows/RDF triples to fetch per batch (defaults to 500).

delete(subject: str, predicate: str, obj: str) → None

Delete a RDF triple from the RDF graph.

Args:

  • subject: Subject of the RDF triple.

  • predicate: Predicate of the RDF triple.

  • obj: Object of the RDF triple.

from_config() → sage.database.postgres_backends.connector.PostgresConnector

Build a DefaultPostgresConnector from a configuration object.

The configuration object must contains the following fields: ‘dbname’, ‘name’, ‘user’ and ‘password’. Optional fields are: ‘host’, ‘port’ and ‘fetch_size’.

insert(subject: str, predicate: str, obj: str) → None

Insert a RDF triple into the RDF graph.

Args:

  • subject: Subject of the RDF triple.

  • predicate: Predicate of the RDF triple.

  • obj: Object of the RDF triple.

search(subject: str, predicate: str, obj: str, last_read: Optional[str] = None, as_of: Optional[datetime.datetime] = None) → Tuple[sage.database.postgres_backends.postgres.iterator.PostgresIterator, int]

Get an iterator over all RDF triples matching a triple pattern.

Args:

  • subject: Subject of the triple pattern.

  • predicate: Predicate of the triple pattern.

  • object: Object of the triple pattern.

  • last_read: A RDF triple ID. When set, the search is resumed for this RDF triple.

  • as_of: A version timestamp. When set, perform all reads against a consistent snapshot represented by this timestamp.

Returns:

A tuple (iterator, cardinality), where iterator is a Python iterator over RDF triples matching the given triples pattern, and cardinality is the estimated cardinality of the triple pattern.

sage.database.postgres_backends.postgres.iterator module

class sage.database.postgres_backends.postgres.iterator.PostgresIterator(cursor, connection, start_query: str, start_params: List[str], pattern: Dict[str, str], fetch_size: int = 500)

Bases: sage.database.db_iterator.DBIterator

A PostgresIterator fetches RDF triples from a PostgreSQL table using batch queries and lazy loading.

Args:

  • cursor: A psycopg cursor. This cursor must only be used for this iterator, to avoid side-effects.

  • connection: A psycopg connection.

  • start_query: Prepared SQL query executed to fetch RDF triples as SQL rows.

  • start_params: Parameters to use with the prepared SQL query.

  • pattern: Triple pattern scanned.

  • fetch_size: The number of SQL rows/RDF triples to fetch per batch.

has_next() → bool

Return True if there is still results to read, False otherwise

last_read() → str

Return the index ID of the last element read

next() → Optional[Dict[str, str]]

Return the next solution mapping or None if there are no more solutions

sage.database.postgres_backends.postgres.queries module

sage.database.postgres_backends.postgres.queries.get_delete_query(table_name: str) → str

Build a SQL query to delete a RDF triple from a PostgreSQL table.

Argument: Name of the SQL table from which the triple will be deleted.

Returns: A prepared SQL query that can be executed with a tuple (subject, predicate, object).

sage.database.postgres_backends.postgres.queries.get_insert_many_query(table_name: str) → str

Build a SQL query to insert several RDF triples into a PostgreSQL table.

Argument: Name of the SQL table in which the triples will be inserted.

Returns: A prepared SQL query that can be executed with a list of tuples (subject, predicate, object).

sage.database.postgres_backends.postgres.queries.get_insert_query(table_name: str) → str

Build a SQL query to insert a RDF triple into a PostgreSQL table.

Argument: Name of the SQL table in which the triple will be inserted.

Returns: A prepared SQL query that can be executed with a tuple (subject, predicate, object).

sage.database.postgres_backends.postgres.queries.get_resume_query(subj: str, pred: str, obj: str, last_read: Tuple[str, str, str], table_name: str, symbol: str = '>=') → Tuple[str, str]

Get a prepared SQL query which resumes scanning for a triple pattern.

The SQL query rely on keyset pagination to resume query processing using an optimized Index Scan.

Args:

  • subj: Subject of the triple pattern.

  • pred: Predicate of the triple pattern.

  • obj: Object of the triple pattern.

  • last_read: The SQL row from whoch to resume scanning.

  • table_name: Name of the SQL table to scan for RDF triples.

  • symbol: Symbol used to perform the keyset pagination. Defaults to “>=”.

Returns:

A tuple with the prepared SQL query and its parameters.

sage.database.postgres_backends.postgres.queries.get_start_query(subj: str, pred: str, obj: str, table_name: str) → Tuple[str, List[str]]

Get a prepared SQL query which starts scanning for a triple pattern.

Args:

  • subj: Subject of the triple pattern.

  • pred: Predicate of the triple pattern.

  • obj: Object of the triple pattern.

  • table_name: Name of the SQL table to scan for RDF triples.

Returns:

A tuple with the prepared SQL query and its parameters.

Module contents