Module com.darkcollective.relix.ast

Package com.darkcollective.relix.ast.internal

Class AttributeNames

java.lang.Object

com.darkcollective.relix.ast.internal.AttributeNames

public final class AttributeNames
extends Object

Utilities for working with possibly relation-qualified attribute names.

An attribute name may carry a relation qualifier separated by a ., for example Users.id. The qualifier is everything up to and including the last .; the column name is everything after it.

Method Summary

Modifier and Type	Method	Description
static boolean	isPathInto(String name, String column)	Whether name is a path into column — dotted, with column as its head: skills.years is a path into skills, while skills and Orders.skills are not.
static String	pathHead(String name)	Returns the head of an attribute name — everything before the first ., or the whole name when it has none: location.city and location.geo.lat both yield location.
static String	qualifierOf(String name)	Returns the relation qualifier of an attribute name, or null if it carries none: rooms.name yields rooms, and a bare name yields null.
static String	stripQualifier(String name)	Strips any relation qualifier from an attribute name, returning the bare column name: Users.id yields id, and a bare id is returned unchanged.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Details

stripQualifier

public static String stripQualifier(String name)

Strips any relation qualifier from an attribute name, returning the bare column name: Users.id yields id, and a bare id is returned unchanged. The qualifier is everything up to and including the last ..

Parameters:

name - a possibly-qualified attribute name; must not be null

Returns:

the unqualified column name

qualifierOf

public static String qualifierOf(String name)

Returns the relation qualifier of an attribute name, or null if it carries none: rooms.name yields rooms, and a bare name yields null. The qualifier is everything up to (but not including) the last ..

Parameters:

name - a possibly-qualified attribute name; must not be null

Returns:

the relation qualifier, or null if the name is unqualified

pathHead

public static String pathHead(String name)

Returns the head of an attribute name — everything before the first ., or the whole name when it has none: location.city and location.geo.lat both yield location.

This is the column a name denotes under the struct-path reading, and it is the other half of a genuine ambiguity. A dotted name may be a relation-qualified reference (Orders.amount — the column amount coming from Orders, whose column part is the tail, see stripQualifier(java.lang.String)) or a path into a nested column (location.city — the field city of the column location, whose column part is the head). The two readings are told apart against a schema, by Schema.resolvePath, and never by the spelling alone.

Reach for this wherever a decision is about which column a reference touches — a rewrite that moves an operator past the column, say. Using the qualifier reading alone there is the mistake it exists to prevent: the head of skills.years is skills, and a rule that only inspected the tail years would conclude the reference has nothing to do with a skills column.

Parameters:

name - a possibly-qualified or dotted attribute name; must not be null

Returns:

the name's head — the column it names as a path

isPathInto

public static boolean isPathInto(String name,
 String column)

Whether name is a path into column — dotted, with column as its head: skills.years is a path into skills, while skills and Orders.skills are not.

Parameters:

name - a possibly-qualified or dotted attribute name; must not be null

column - the column to test against; must not be null

Returns:

whether the name reads a field beneath that column