Class TopicSelectors

parse

• parse(expression: string | TopicSelector | Array<string | TopicSelector>, ...args: Array<string | TopicSelector>): TopicSelector

• Parse an expression to create a selector.

  This function can take any number of arguments. Each argument can be a string or a TopicSelector. Alternatively, an array of strings and TopicSelectors can be passed as a single argument.

  The following types of expression are supported. The type is determined by the first character of the expression.

  Path

  Path expressions begin with the character >. The remainder of the expression must be a valid topic path. A topic path is a '/' separated string of parts. Each part is formed of one or more UTF characters, except '/'.

  A PATH selector is returned that only selects the topic with the given path.

  Abbreviated Path Expressions

  In Diffusion 5.2, an alternative syntax for path expressions was added. An abbreviated path expression is any valid topic path (see above) that begins with a character other than one of #, ?, >, *, $, %, &, or <. This syntax allows most topic paths to be used directly as selector expressions which appears more natural.

  This method converts abbreviated path expressions to standard path expressions by prepending the > character. Thus a/b is interpreted as >a/b.

  parse("a/b").expression will return ">a/b".

  Split-path pattern

  Split-path pattern expressions begin with the character ?. The remainder of the expression is split into a list of regular expressions using the / character as a separator.

  A SPLIT_PATH_PATTERN selector is returned that selects topics for which each regular expression matches each part of the topic path at the corresponding level.

  Full-path pattern

  Full-path pattern expressions begin with the character *. The remainder of the pattern is a regular expression.

  A FULL_PATH_PATTERN selector is returned that selects topics for which the regular expression matches the complete topic path.

  Full-path patterns provide a lot of expressive power but should be used sparingly since the server can evaluate split-path patterns more efficiently.

  Selector sets are the preferred way to combine expressions. parse("a", "b") is equivalent to the full-path expression " *[a|b]", but can be evaluated more efficiently by the server.

  Selector set

  Selector set expressions begin with the character #. The remainder of the expression is a list of contained selectors, formatted as described below.

  A SELECTOR_SET selector is returned that selects topics that match any of the contained selectors.

  The contained selectors are formatted as follows. First, any selector sets are expanded to produce a full list of non-selector set expressions. Then the selector expressions are concatenated, separated by the separator ////. This separator has been chosen as it is not valid in a path, and is not a useful sequence in a pattern.

  Descendant pattern qualifiers

  Split-path and full-path pattern expressions can be further modified by appending / or //. These control the behaviour of the selector with respect to the descendants of the topics that match the pattern.

  • If the expression does not end with `/` or `//`, it selects only the topics that match the pattern.
  • If the expression ends with `/`, it selects only the descendants of the matching topics, excluding the matching topics.
  • If the expression ends with `//`, it selects the matching topics and all of their descendants.

  Regular expressions

  Any Java-style regular expression can be used in split-path and full-path patterns, with the following restrictions:

  • A regular expression may not be empty.
  • A regular expression used in split-path patterns may not contain the path separator /.
  • A regular expression used in full-path patterns may not contain the selector set separator ////.

  Regular expressions that break any of these restrictions would never match a topic path, so they make no practical difference.

  Examples

  Path expressions

  Path	Matches alpha/beta?	Matches alpha/beta/gamma?
  >alpha/beta	yes	no
  >alpha/beta/gamma	no	yes
  >beta	no	no
  >.*`/.*`	no	no
  >/alpha/beta/	yes	no

  Abbreviated path expressions

  Path	Matches alpha/beta?	Matches alpha/beta/gamma?
  alpha/beta	yes	no
  alpha/beta/gamma	no	yes
  beta	no	no
  /alpha/beta/	yes	no

  Split-path pattern expressions

  Path	Matches alpha/beta?	Matches alpha/beta/gamma?
  ?alpha/beta	yes	no
  ?alpha/beta/gamma	no	yes
  ?beta	no	no
  ?.*	no	no
  ?.*`/.*`	yes	no
  ?alpha/beta/	no	yes
  ?alpha/beta//	yes	yes
  ?alpha/.*`//`	yes	yes

  Full-path pattern expressions

  Path	Matches alpha/beta?	Matches alpha/beta/gamma?
  *alpha/beta	yes	no
  *alpha/beta/gamma	no	yes
  *beta	no	no
  *.*beta	yes	no
  *.*	yes	yes
  *alpha/beta/	no	yes
  *alpha/beta//	yes	yes

  Example:

  // Simple selector
  var selector = diffusion.selectors.parse(">a/b");

  Example:

  // Creating a selector set
  var selectorSet = diffusion.selectors.parse(">a", ">b");

  Parameters

  • expression: string | TopicSelector | Array<string | TopicSelector>

    the pattern expression(s). At least one valid selector has to be specified.

  • Rest ...args: Array<string | TopicSelector>

    additional pattern expressions

  Returns TopicSelector

  the topic selector. If multiple expressions are provided, this will return a SELECTOR_SET that will match if any of the * provided selectors match.