TimespanDatabaseRepresentation

class lsst.daf.butler.TimespanDatabaseRepresentation

Bases: lsst.daf.butler.TopologicalExtentDatabaseRepresentation

Representation of a time span within a database engine.

Provides an interface that encapsulates how timespans are represented in a database engine.

Most of this class’s interface is comprised of classmethods. Instances can be constructed via the fromSelectable or fromLiteral methods as a way to include timespan overlap operations in query JOIN or WHERE clauses.

Notes

TimespanDatabaseRepresentation implementations are guaranteed to use the same interval definitions and edge-case behavior as the Timespan class. They are also guaranteed to round-trip Timespan instances exactly.

Attributes Summary

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

Methods Summary

contains(other, …)	Return a SQLAlchemy expression representing containment.
extract(mapping, Any], name, None] = None)	Extract a region from a dictionary.
flatten(name, None])	Return the actual column(s) that comprise this logical column.
fromLiteral(timespan)	Construct a database timespan from a literal Timespan instance.
fromSelectable(selectable, name, None] = None)	Construct representation of a column in the table or subquery.
getFieldNames(name, None] = None)	Return the actual field names used by this representation.
hasExclusionConstraint()	Return True if this representation supports exclusion constraints.
isEmpty()	Return a boolean SQLAlchemy expression for testing empty timespans.
isNull()	Return expression that tests where region is NULL.
lower()	Return a SQLAlchemy expression representing a lower bound of a timespan.
makeFieldSpecs(nullable, name, None] = None, …)	Make objects that reflect the fields that must be added to table.
overlaps(other)	Return a SQLAlchemy expression representing timespan overlaps.
update(extent, None], name, None] = None, …)	Add a region to a dictionary.
upper()	Return a SQLAlchemy expression representing an upper bound of a timespan.

Attributes Documentation

NAME = 'timespan'

SPACE = 2

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

contains(other: Union[_S, sqlalchemy.sql.elements.ColumnElement]) → sqlalchemy.sql.elements.ColumnElement

Return a SQLAlchemy expression representing containment.

Returns a test for whether an in-database timespan contains another timespan or a time point.

Parameters:

other : type(self) or sqlalchemy.sql.ColumnElement

The timespan or time to relate to self; either an instance of the same TimespanDatabaseRepresentation subclass as self, or a SQL column expression representing an astropy.time.Time.

Returns:

contains : sqlalchemy.sql.ColumnElement

A boolean SQLAlchemy expression object.

Notes

See Timespan.contains for edge-case behavior.

classmethod extract(mapping: Mapping[str, Any], name: Optional[str, None] = None) → Optional[_R, None]

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, None]) → 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 fromLiteral(timespan: lsst.daf.butler.core.timespan.Timespan) → _S

Construct a database timespan from a literal Timespan instance.

Parameters:

timespan : Timespan

Literal timespan to convert.

Returns:

tsRepr : TimespanDatabaseRepresentation

A timespan expression object backed by sqlalchemy.sql.literal column expressions.

classmethod fromSelectable(selectable: sqlalchemy.sql.selectable.FromClause, name: Optional[str, None] = None) → _S

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] = 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.

isEmpty() → sqlalchemy.sql.elements.ColumnElement

Return a boolean SQLAlchemy expression for testing empty timespans.

Returns:

empty : sqlalchemy.sql.ColumnElement

A boolean SQLAlchemy expression object.

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.

lower() → sqlalchemy.sql.elements.ColumnElement

Return a SQLAlchemy expression representing a lower bound of a timespan.

Returns:

lower : sqlalchemy.sql.ColumnElement

A SQLAlchemy expression for a lower bound.

Notes

If database holds NULL for a timespan then the returned expression should evaluate to 0. Main purpose of this and upper method is to use them in generating SQL, in particular ORDER BY clause, to guarantee a predictable ordering. It may potentially be used for transforming boolean user expressions into SQL, but it will likely require extra attention to ordering issues.

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

Make objects that reflect 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.

overlaps(other: _S) → sqlalchemy.sql.elements.ColumnElement

Return a SQLAlchemy expression representing timespan overlaps.

Parameters:

other : type(self)

The timespan to overlap self with.

Returns:

overlap : sqlalchemy.sql.ColumnElement

A boolean SQLAlchemy expression object.

Notes

See Timespan.overlaps for edge-case behavior.

classmethod update(extent: Optional[_R, None], name: Optional[str, None] = None, result: Optional[Dict[str, Any], None] = 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.

upper() → sqlalchemy.sql.elements.ColumnElement

Return a SQLAlchemy expression representing an upper bound of a timespan.

Returns:

upper : sqlalchemy.sql.ColumnElement

A SQLAlchemy expression for an upper bound.

Notes

If database holds NULL for a timespan then the returned expression should evaluate to 0. Also see notes for lower method.