DimensionElement¶
-
class
lsst.daf.butler.
DimensionElement
¶ Bases:
lsst.daf.butler.TopologicalRelationshipEndpoint
A named data-organization concept that defines a label and/or metadata in the dimensions system.
A
DimensionElement
instance typically corresponds to a _logical_ table in theRegistry
: either an actual database table or a way of generating rows on-the-fly that can similarly participate in queries. The rows in that table are represented by instances of aDimensionRecord
subclass. MostDimensionElement
instances are instances of itsDimension
subclass, which is used for elements that can be used as data ID keys.Notes
DimensionElement
instances should always be constructed by and retreived from aDimensionUniverse
. They are immutable after they are fully constructed, and should never be copied.Pickling a
DimensionElement
just records its name and universe; unpickling one actually just looks up the element via the singleton dictionary of all universes. This allows pickle to be used to transfer elements between processes, but only when each process initializes its own instance of the sameDimensionUniverse
.Attributes Summary
RecordClass
The DimensionRecord
subclass used to hold records for this element (type
).alwaysJoin
If True
, always include this element in any query or data ID in which itsrequired
dimensions appear, because it defines a relationship between those dimensions that must always be satisfied.dimensions
The union of required
andimplied
, with all elements inrequired
before any elements inimplied
.governor
The GovernorDimension
that is a required dependency of this element, orNone
if there is no such dimension (GovernorDimension
orNone
).graph
Minimal graph that includes this element ( DimensionGraph
).implied
Other dimensions that are uniquely identified directly by a record of this dimension element. metadata
Additional metadata fields included in this element’s table ( NamedValueSet
ofFieldSpec
).name
Unique string identifier for this endpoint ( str
).required
Dimensions that are necessary to uniquely identify a record of this dimension element. spatial
This endpoint’s SPATIAL
family.temporal
This endpoint’s TEMPORAL
family.topology
The relationship families to which this endpoint belongs, keyed by the category for that family. viewOf
Name of another table this element’s records are drawn from ( str
orNone
).Methods Summary
hasTable
()Return True
if this element is associated with a table (even if that table “belongs” to another element).Attributes Documentation
-
RecordClass
¶ The
DimensionRecord
subclass used to hold records for this element (type
).Because
DimensionRecord
subclasses are generated dynamically, this type cannot be imported directly and hence can only be obtained from this attribute.
-
alwaysJoin
¶ If
True
, always include this element in any query or data ID in which itsrequired
dimensions appear, because it defines a relationship between those dimensions that must always be satisfied.
-
dimensions
¶ The union of
required
andimplied
, with all elements inrequired
before any elements inimplied
.This differs from
self.graph.dimensions
both in order and in content:- as in
self.implied
, implied dimensions are not expanded recursively here; - implied dimensions appear after required dimensions here, instead of being topologically ordered.
As a result, this set is ordered consistently with
self.RecordClass.fields
.- as in
-
governor
¶ The
GovernorDimension
that is a required dependency of this element, orNone
if there is no such dimension (GovernorDimension
orNone
).
-
graph
¶ Minimal graph that includes this element (
DimensionGraph
).self.graph.required
includes all dimensions whose primary key values are sufficient (often necessary) to uniquely identifyself
(includingself
ifisinstance(self, Dimension)
.self.graph.implied
includes all dimensions also identified (possibly recursively) by this set.
-
implied
¶ Other dimensions that are uniquely identified directly by a record of this dimension element.
For elements with a database representation, these are exactly the dimensions used to form foreign key constraints whose fields are not (wholly) also part of the primary key.
Unlike
self.graph.implied
, this set is not expanded recursively.
-
metadata
¶ Additional metadata fields included in this element’s table (
NamedValueSet
ofFieldSpec
).
-
required
¶ Dimensions that are necessary to uniquely identify a record of this dimension element.
For elements with a database representation, these dimension are exactly those used to form the (possibly compound) primary key, and all dimensions here that are not
self
are also used to form foreign keys.For
Dimension
instances, this should be exactly the same asgraph.required
, but that may not be true forDimensionElement
instances in general. When they differ, there are multiple combinations of dimensions that uniquely identify this element, but this one is more direct.
-
topology
¶ The relationship families to which this endpoint belongs, keyed by the category for that family.
Methods Documentation
-