TopologicalExtentDatabaseRepresentation

class lsst.daf.butler.TopologicalExtentDatabaseRepresentation(*args, **kwds)

Bases: Generic[lsst.daf.butler.core._topology._R]

Mapping of in-memory representation of a region to DB representation.

An abstract base class whose subclasses provide a mapping from the in-memory representation of a TopologicalSpace region to a database-storage representation, and whose instances act like a SQLAlchemy-based column expression.

Attributes Summary

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

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

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

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.

abstract 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.

abstract classmethod fromSelectable(selectable: sqlalchemy.sql.selectable.FromClause, name: Optional[str] = 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

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.

abstract 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.

abstract 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.

abstract 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.

abstract classmethod update(extent: Optional[_R], 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.