SpatialRegionDatabaseRepresentation

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

Bases: lsst.daf.butler.TopologicalExtentDatabaseRepresentation[lsst.sphgeom._sphgeom.Region]

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

columnsqlalchemy.sql.ColumnElement

Column containing the opaque byte-string, with automatic conversion to lsst.sphgeom.Region implemented via SQLAlchemy hooks.

namestr

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	Name to use for this logical column in tables (str).
SPACE	Topological space where regions represented by this class exist.
name	Return base logical name for the topological extent (str).

Methods Summary

extract(mapping[, 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])	Make objects that relfect the fields that must be added to table.
update(extent[, name, result])	Add a region to a dictionary.

Attributes Documentation

NAME: ClassVar[str] = 'region'

Name to use for this logical column in tables (str).

If the representation actually uses multiple columns, this will just be part of the names of those columns. Queries (and tables that represent materialized queries) may use a different name (via the name parameters to various methods) in order to disambiguate between the regions associated with different tables.

SPACE: ClassVar[lsst.daf.butler.TopologicalSpace] = 1

Topological space where regions represented by this class exist.

name

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

mappingMapping [ 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.

namestr, 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

namestr, 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

columnsIterator [ 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.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

selectablesqlalchemy.sql.FromClause

SQLAlchemy object representing a table or subquery.

namestr, optional

Name for the logical column; a part of the name for multi-column representations. Defaults to cls.NAME.

Returns

representationTopologicalExtentDatabaseRepresentation

Object representing a logical column.

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

Return the actual field names used by this representation.

Parameters

namestr, optional

Name for the logical column; a part of the name for multi-column representations. Defaults to cls.NAME.

Returns

namestuple [ 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

supportedbool

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

isnullsqlalchemy.sql.ColumnElement

A boolean SQLAlchemy expression object.

classmethod makeFieldSpecs(nullable: bool, name: Optional[str] = None, **kwargs: Any) → 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

nullablebool

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 (-∞, ∞).

namestr, 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

specstuple [ 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.

namestr, optional

Name for the logical column; a part of the name for multi-column representations. Defaults to cls.NAME.

resultdict [ 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

resultdict [ str, Any ]

A dictionary containing this representation of a region. Exactly the dict passed as result if that is not None.