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 the Registry: 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 a DimensionRecord subclass. Most DimensionElement instances are instances of its Dimension 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 a DimensionUniverse. 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 same DimensionUniverse.

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 its `required` dimensions appear, because it defines a relationship between those dimensions that must always be satisfied.
`dimensions`	The union of `required` and `implied`, with all elements in `required` before any elements in `implied`.
`governor`	The `GovernorDimension` that is a required dependency of this element, or `None` if there is no such dimension (`GovernorDimension` or `None`).
`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` of `FieldSpec`).
`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` or `None`).

Methods Summary

`from_json`(json_str, universe, registry)	Convert a JSON string created by `to_json` and return something of the supplied class.
`from_simple`(simple, universe, registry)	Construct a new object from the data returned from the `to_simple` method.
`hasTable`()	Return `True` if this element is associated with a table (even if that table “belongs” to another element).
`to_json`(minimal)	Convert this class to JSON form.
`to_simple`(minimal)	Convert this class to a simple python type suitable for serialization.

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 its required dimensions appear, because it defines a relationship between those dimensions that must always be satisfied.

dimensions¶

The union of required and implied, with all elements in required before any elements in implied.

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.

governor¶: The GovernorDimension that is a required dependency of this element, or None if there is no such dimension (GovernorDimension or None).

graph¶

Minimal graph that includes this element (DimensionGraph).

self.graph.required includes all dimensions whose primary key values are sufficient (often necessary) to uniquely identify self (including self if isinstance(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 of FieldSpec).

name¶: Unique string identifier for this endpoint (str).

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 as graph.required, but that may not be true for DimensionElement instances in general. When they differ, there are multiple combinations of dimensions that uniquely identify this element, but this one is more direct.

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 or None).

Methods Documentation

classmethod from_json(json_str: str, universe: Optional[DimensionUniverse] = None, registry: Optional[Registry] = None) → SupportsSimple¶

Convert a JSON string created by to_json and return something of the supplied class.

Parameters:	json_str : `str` Representation of the dimensions in JSON format as created by `to_json()`. universe : `DimensionUniverse`, optional The special graph of all known dimensions. Passed directly to `from_simple()`. registry : `lsst.daf.butler.Registry`, optional Registry to use to convert simple name of a DatasetType to a full `DatasetType`. Passed directly to `from_simple()`.
Returns:	constructed : Any Newly-constructed object.

classmethod from_simple(simple: str, universe: Optional[DimensionUniverse] = None, registry: Optional[Registry] = None) → DimensionElement¶

Construct a new object from the data returned from the to_simple method.

Parameters:	simple : `str` The value returned by `to_simple()`. universe : `DimensionUniverse` The special graph of all known dimensions. registry : `lsst.daf.butler.Registry`, optional Registry from which a universe can be extracted. Can be `None` if universe is provided explicitly.
Returns:	dataId : `DimensionElement` Newly-constructed object.

hasTable() → bool¶: Return True if this element is associated with a table (even if that table “belongs” to another element).

to_json(minimal: bool = False) → str¶

Convert this class to JSON form.

The class type is not recorded in the JSON so the JSON decoder must know which class is represented.

Parameters:	minimal : `bool`, optional Use minimal serialization. Requires Registry to convert back to a full type.
Returns:	json : `str` The class in JSON string format.

to_simple(minimal: bool = False) → str¶

Convert this class to a simple python type suitable for serialization.

Parameters:	minimal : `bool`, optional Use minimal serialization. Has no effect on for this class.
Returns:	simple : `str` The object converted to a single string.

Navigation

DimensionElement¶