SpatialRegionDatabaseRepresentation¶

class lsst.daf.butler.SpatialRegionDatabaseRepresentation(column: sqlalchemy.sql.elements.ColumnElement, name: str)¶

Bases: lsst.daf.butler.TopologicalExtentDatabaseRepresentation

Class reflecting how spatial regions are represented inside the DB.

An instance of this class encapsulates how spatial regions on the sky are represented in a database engine.

Instances should be constructed via fromSelectable, not by calling the constructor directly.

Parameters:	column : `sqlalchemy.sql.ColumnElement` Column containing the opaque byte-string, with automatic conversion to `lsst.sphgeom.Region` implemented via SQLAlchemy hooks. name : `str` Name of the column.

Notes

Unlike TimespanDatabaseRepresentation, this is a concrete class, because we currently do not support any database-native spatial regions, and instead rely on precomputed overlaps and opaque (to the database) byte string columns. As a result, it also does not support any in-database topological predicates.

If we add support for database-native regions in the future, this class may become an ABC with multiple concrete implementations.

Attributes Summary

`NAME`
`SPACE`
`name`	Return base logical name for the topological extent (`str`).

Methods Summary

`extract`(mapping, Any], name)	Extract a region from a dictionary.
`flatten`(name)	Return the actual column(s) that comprise this logical column.
`fromSelectable`(selectable, name)	Construct representation of a column in the table or subquery.
`getFieldNames`(name)	Return the actual field names used by this representation.
`hasExclusionConstraint`()	Return `True` if this representation supports exclusion constraints.
`isNull`()	Return expression that tests where region is `NULL`.
`makeFieldSpecs`(nullable, name, **kwargs)	Make objects that relfect the fields that must be added to table.
`update`(extent, name, result, Any]] = None)	Add a region to a dictionary.

Attributes Documentation

NAME = 'region'¶

SPACE = 1¶

name¶

Return base logical name for the topological extent (str).

If the representation uses only one actual column, this should be the full name of the column. In other cases it is an unspecified subset of the column names.

Methods Documentation

classmethod extract(mapping: Mapping[str, Any], name: Optional[str] = None) → Optional[lsst.sphgeom._sphgeom.Region]¶

Extract a region from a dictionary.

This region represents a database row in this representation.

Parameters:	mapping : `Mapping` [ `str`, `Any` ] A dictionary representing a database row containing a `Timespan` in this representation. Should have key(s) equal to the return value of `getFieldNames`. name : `str`, optional Name for the logical column; a part of the name for multi-column representations. Defaults to `cls.NAME`.
Returns:	region Python representation of the region.

flatten(name: Optional[str]) → Iterator[sqlalchemy.sql.elements.ColumnElement]¶

Return the actual column(s) that comprise this logical column.

Parameters:	name : `str`, optional If provided, a name for the logical column that should be used to label the columns. If not provided, the columns’ native names will be used.
Returns:	columns : `Iterator` [ `sqlalchemy.sql.ColumnElement` ] The true column or columns that back this object.

classmethod fromSelectable(selectable: sqlalchemy.sql.selectable.FromClause, name: Optional[str] = None) → lsst.daf.butler.core._topology.SpatialRegionDatabaseRepresentation¶

Construct representation of a column in the table or subquery.

Constructs an instance that represents a logical column (which may actually be backed by multiple columns) in the given table or subquery.

Parameters:	selectable : `sqlalchemy.sql.FromClause` SQLAlchemy object representing a table or subquery. name : `str`, optional Name for the logical column; a part of the name for multi-column representations. Defaults to `cls.NAME`.
Returns:	representation : `TopologicalExtentDatabaseRepresentation` Object representing a logical column.

classmethod getFieldNames(name: Optional[str] = None) → Tuple[str, ...]¶

Return the actual field names used by this representation.

Parameters:	name : `str`, optional Name for the logical column; a part of the name for multi-column representations. Defaults to `cls.NAME`.
Returns:	names : `tuple` [ `str` ] Field name(s). Guaranteed to be the same as the names of the field specifications returned by `makeFieldSpecs`.

classmethod hasExclusionConstraint() → bool¶

Return True if this representation supports exclusion constraints.

Returns:	supported : `bool` If `True`, defining a constraint via `ddl.TableSpec.exclusion` that includes the fields of this representation is allowed.

isNull() → sqlalchemy.sql.elements.ColumnElement¶

Return expression that tests where region is NULL.

Returns a SQLAlchemy expression that tests whether this region is logically NULL.

Returns:	isnull : `sqlalchemy.sql.ColumnElement` A boolean SQLAlchemy expression object.

classmethod makeFieldSpecs(nullable: bool, name: Optional[str] = None, **kwargs) → Tuple[lsst.daf.butler.core.ddl.FieldSpec, ...]¶

Make objects that relfect the fields that must be added to table.

Makes one or more ddl.FieldSpec objects that reflect the fields that must be added to a table for this representation.

Parameters:

nullable : bool: If True, the region is permitted to be logically NULL (mapped to None in Python), though the correspoding value(s) in the database are implementation-defined. Nullable region fields default to NULL, while others default to (-∞, ∞).
name : str, optional: Name for the logical column; a part of the name for multi-column representations. Defaults to cls.NAME.
**kwargs: Keyword arguments are forwarded to the ddl.FieldSpec constructor for all fields; implementations only provide the name, dtype, and default arguments themselves.

Returns:

specs : tuple [ ddl.FieldSpec ]: Field specification objects; length of the tuple is subclass-dependent, but is guaranteed to match the length of the return values of getFieldNames and update.

classmethod update(extent: Optional[lsst.sphgeom._sphgeom.Region], name: Optional[str] = None, result: Optional[Dict[str, Any]] = None) → Dict[str, Any]¶

Add a region to a dictionary.

This region represents a database row in this representation.

Parameters:

extent: An instance of the region type this class provides a database representation for, or None for NULL.
name : str, optional: Name for the logical column; a part of the name for multi-column representations. Defaults to cls.NAME.
result : dict [ str, Any ], optional: A dictionary representing a database row that fields should be added to, or None to create and return a new one.

Returns:

result : dict [ str, Any ]: A dictionary containing this representation of a region. Exactly the dict passed as result if that is not None.

Navigation

SpatialRegionDatabaseRepresentation¶