Template Class Key

Inheritance Relationships

Base Types

Class Documentation

template<typename T>
class Key : public lsst::afw::table::KeyBase<T>, public lsst::afw::table::FieldBase<T>

A class used as a handle to a particular field in a table.

All access to table data ultimately goes through Key objects, which know (via an internal offset) how to address and cast the internal data buffer of a record or table.

Keys can be obtained from a Schema by name: 

schema.find("myfield").key

and are also returned when a new field is added. Compound and array keys also provide accessors to retrieve scalar keys to their elements (see the documentation for the KeyBase specializations), even though these element keys do not correspond to a field that exists in any Schema. For example: 

Schema schema;
Key< Array<float> > arrayKey = schema.addField< Array<float> >("array", "docs for array", 5);
Key< Point<int> > pointKey = schema.addField< Point<int> >("point", "docs for point");
Key<float> elementKey = arrayKey[3];
Key<int> xKey = pointKey.getX();
std::shared_ptr<BaseTable> table = BaseTable::make(schema);
std::shared_ptr<BaseRecord> record = table.makeRecord();
assert(&record[arrayKey][3] == &record[elementKey3]);
assert(record.get(pointKey).getX() == record[xKey]);

Key inherits from FieldBase to allow a key for a dynamically-sized field to know its size without needing to specialize Key itself or hold a full Field object.

Unnamed Group

template<typename OtherT>
bool operator==(Key<OtherT> const &other) const

Equality comparison.

Two keys with different types are never equal. Keys with the same type are equal if they point to the same location in a table, regardless of what Schema they were constructed from (for instance, if a field has a different name in one Schema than another, but is otherwise the same, the two keys will be equal).

template<typename OtherT>
bool operator!=(Key<OtherT> const &other) const
bool operator==(Key const &other) const
bool operator!=(Key const &other) const

Public Functions

std::size_t hash_value() const

Return a hash of this object.

int getOffset() const

Return the offset (in bytes) of this field within a record.

bool isValid() const

Return true if the key was initialized to valid offset.

This does not guarantee that a key is valid with any particular schema, or even that any schemas still exist in which this key is valid.

A key that is default constructed will always be invalid.

Key()

Default construct a field.

The new field will be invalid until a valid Key is assigned to it.

Key(Key const&)
Key(Key&&)
Key &operator=(Key const&)
Key &operator=(Key&&)
~Key()

Friends

friend lsst::afw::table::Key::detail::Access
std::ostream &operator<<(std::ostream &os, Key<T> const &key)

Stringification.