Class Schema

Class Documentation

class Schema

Defines the fields and offsets for a table.

Schema behaves like a container of SchemaItem objects, mapping a descriptive Field object with the Key object used to access record and ColumnView values. A Schema is the most important ingredient in creating a table.

Because offsets for fields are assigned when the field is added to the Schema, Schemas do not support removing fields, though they do allow renaming.

Field names in Schemas are expected to be underscore-separated names (e.g. ‘a_b_c’, but see afwTableFieldNames for the full conventions, including when to use underscores vs. CamelCase). The SubSchema class and Schema::operator[] provide a heirarchical interface to these names, but are implemented entirely as string splitting/joining operations that ultimately forward to member functions that operate on the fully-qualified field name, so there is no requirement that names be separated by underscores, and no performance advantage to using a SubSchema.

A SchemaMapper object can be used to define a relationship between two Schemas to be used when copying values from one table to another or loading/saving selected fields to disk.

Schema uses copy-on-write, and hence should always be held by value rather than smart pointer. When creating a Python interface, functions that return Schema by const reference should be converted to return by value (returnCopy) to ensure proper memory management and encapsulation.

Unnamed Group

std::string join(std::string const &a, std::string const &b) const

Join strings using the field delimiter appropriate for this Schema.

std::string join(std::string const &a, std::string const &b, std::string const &c) const
std::string join(std::string const &a, std::string const &b, std::string const &c, std::string const &d) const

Unnamed Group

bool operator==(Schema const &other) const

Equality comparison

Schemas are considered equal according the standard equality operator if their sequence of keys are identical (same types with the same offsets); names and descriptions of fields are not considered. For a more precise comparison, use compare() or contains().

bool operator!=(Schema const &other) const

Public Types

enum ComparisonFlags

Bit flags used when comparing schemas.

All quantities are compared in insertion order, so if two schemas have the same fields added in opposite order, they will not be considered equal.

Values:

EQUAL_KEYS = 0x01

Keys have the same types offsets, and sizes.

EQUAL_NAMES = 0x02

Fields have the same names (ordered).

EQUAL_DOCS = 0x04

Fields have the same documentation (ordered).

EQUAL_UNITS = 0x08

Fields have the same units (ordered).

EQUAL_FIELDS = 0x0F

Fields are identical (but aliases may not be).

EQUAL_ALIASES = 0x10

Schemas have identical AliasMaps.

IDENTICAL = 0x1F

Everything is the same.

Public Functions

template<typename T>
SchemaItem<T> find(std::string const &name) const

Find a SchemaItem in the Schema by name.

Names corresponding to named subfields are accepted, and will return a SchemaItem whose field is copied from the parent field with only the name changed.

template<typename T>
SchemaItem<T> find(Key<T> const &key) const

Find a SchemaItem in the Schema by key.

Keys corresponding to named subfields are accepted, and will return a SchemaItem whose field is copied from the parent field with only the name changed. Keys corresponding to unnamed subfields (such as array elements) are not accepted.

template<typename F>
void findAndApply(std::string const &name, F &&func) const

Find a SchemaItem by name and run a functor on it.

Names corresponding to named subfields are not accepted. The given functor must have an overloaded function call operator that accepts any SchemaItem type (the same as a functor provided to forEach).

SubSchema operator[](std::string const &name) const

Look up a (possibly incomplete) name in the Schema.

See SubSchema for more information.

This member function should generally only be used on “finished” Schemas; modifying a Schema after a SubSchema to it has been constructed will not allow the proxy to track the additions, and will invoke the copy-on-write mechanism of the Schema itself.

std::set<std::string> getNames(bool topOnly = false) const

Return a set of field names in the schema.

If topOnly==true, return a unique list of only the part of the names before the first underscore. For example, if the full list of field names is [‘a_b_c’, ‘a_d’, ‘e_f’], topOnly==true will return [‘a’, ‘e’].

Returns an instance of Python’s builtin set in Python.

Aliases are not returned.

int getRecordSize() const

Return the raw size of a record in bytes.

int getFieldCount() const

The total number of fields.

int getFlagFieldCount() const

The number of Flag fields.

int getNonFlagFieldCount() const

The number of non-Flag fields.

template<typename T>
Key<T> addField(Field<T> const &field, bool doReplace = false)

Add a new field to the Schema, and return the associated Key.

The offsets of fields are determined by the order they are added, but may be not contiguous (the Schema may add padding to align fields, and how much padding is considered an implementation detail).

If doReplace is true and the field exists, it will be replaced instead of throwing an exception.

template<typename T>
Key<T> addField(std::string const &name, std::string const &doc, std::string const &units = "", FieldBase<T> const &base = FieldBase<T>(), bool doReplace = false)

Add a new field to the Schema, and return the associated Key.

This is simply a convenience wrapper, equivalent to: 

addField(Field<T>(name, doc, units, base), doReplace)

template<typename T>
Key<T> addField(std::string const &name, std::string const &doc, FieldBase<T> const &base, bool doReplace = false)

Add a new field to the Schema, and return the associated Key.

This is simply a convenience wrapper, equivalent to: 

addField(Field<T>(name, doc, base), doReplace)

template<typename T>
void replaceField(Key<T> const &key, Field<T> const &field)

Replace the Field (name/description) for an existing Key.

template<typename F>
void forEach(F &&func) const

Apply a functor to each SchemaItem in the Schema.

The functor must have a templated or sufficiently overloaded operator() that supports SchemaItems of all supported field types - even those that are not present in this particular Schema.

Fields will be processed in the order they were added to the schema.

std::size_t hash_value() const

Return a hash of this object.

int compare(Schema const &other, int flags = EQUAL_KEYS) const

Do a detailed equality comparison of two schemas.

See ComparisonFlags for a description of the possible return values

Parameters

  • [in] other: The other schema to compare to.

  • [in] flags: Which types of comparisions to perform. Flag bits not present here will never be returned.

int contains(Schema const &other, int flags = EQUAL_KEYS) const

Test whether the given schema is a subset of this.

This function behaves very similarly to compare(), but ignores fields that are present in this but absent in other.

template<typename T>
int contains(SchemaItem<T> const &item, int flags = EQUAL_KEYS) const

Return true if the given item is in this schema.

The flags must include the EQUAL_KEYS bit, and if the item cannot be found by key no bits will be set on return.

std::shared_ptr<AliasMap> getAliasMap() const

Return the map of aliases

Note that while this is a const method, it does allow the Schema’s aliases to be edited - this allows the aliases to be modified even after a Table has been constructed from the Schema.

See AliasMap for more information on schema aliases.

void setAliasMap(std::shared_ptr<AliasMap> aliases)

Set the alias map

This resets the internal pointer to the alias map, disconnecting this schema from any others it shares aliases with.

Passing a null pointer is equivalent to passing an empty map.

void disconnectAliases()

Sever the connection between this schema and any others with which it shares aliases.

Schema()

Construct an empty Schema.

Schema(Schema const &other)

Copy constructor.

Schema(Schema &&other)
Schema &operator=(Schema const &other)
Schema &operator=(Schema &&other)
~Schema()

Public Static Functions

static Schema readFits(std::string const &filename, int hdu = fits::DEFAULT_HDU)

Construct from reading a FITS file.

Reads from the nominated ‘hdu’ (0=PHU which cannot be a catalog, afw::fits::DEFAULT_HDU is a special value meaning read from the first HDU with NAXIS != 0).

static Schema readFits(fits::MemFileManager &manager, int hdu = fits::DEFAULT_HDU)
static Schema readFits(fits::Fits &fitsfile)
static Schema fromFitsMetadata(daf::base::PropertyList &header, bool stripMetadata = true)

Construct from reading a FITS header

If ‘stripMetadata’, then the header will be modified, removing the relevant keywords.

Public Static Attributes

int const VERSION = detail::SchemaImpl::VERSION

Friends

friend lsst::afw::table::Schema::detail::Access
std::ostream &operator<<(std::ostream &os, Schema const &schema)

Stringification.