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internal package
Foswiki::Query::Node is a
Foswiki::Infix::Node
A Node object is a single node in a query (either a tree node or a leaf node).
A tree of node objects represents a query over the Foswiki database.
Fields are given by name, and values by strings or numbers.
A query object implements the
evaluate
method as its general
contract with the rest of the world. This method is a "reference implementation" -
it does a brute force evaluation of the expression represented by the node in a given
data domain. It is expected that smarter store implementations will analyse the parse tree
and derive as many optimisations as possible, minimising fallback to this brute force
evaluation.
The reference implementation of evaluation uses the
getField
method in the
{Store}{QueryAlgorithm} to get data from the store. This further decouples the query
object from the detail of the store implementation.
See
Foswiki::Store::QueryAlgorithms for a full spec of the interface to
query algorithms.
PUBLIC %aliases
A hash mapping short aliases for META: entry names. For example, this hash
maps 'form' to 'META:FORM'. Published because extensions (search
implementations) have made use of it in the past, though not part of the
offical API.
This hash is maintained by
Foswiki::Meta and is
strictly read-only
PUBLIC %isArrayType
Maps META: entry type names to true if the type is an array type (such as
FIELD, ATTACHMENT or PREFERENCE). Published because extensions (search
implementations) have made use of it in the past, though not part of the
offical API. The type name should be given without the leading 'META:'
This hash is maintained by
Foswiki::Meta and is
strictly read-only
ObjectMethod
evaluate(...) → $result
Evaluate this node by invoking the
evaluate
method of the attached operator.
The return result is either an array ref (for many results) or a scalar (for a
single result)
This is the reference evaluator for queries. However it may not be the only
engine that evaluates them; external engines, such as SQL, might be delegated
the responsibility of evaluating queries in a search context.
Name resolution depends on the context in which the name is used. A name
on the LHS of the dot and where operators may only be a form name, or a META:
name, referred to as a "restricted name". A name anywhere else can be
a META: name, a field name, or one of the shortcuts (such as "web", "name"
etc). Fields and forms are looked up by calling the
getField
and
getForm
methods in the query engine respectively.
ObjectMethod
evaluatesToConstant(%opts)
Support for expression optimisation/hoisting.
Determine if this node evaluates to a constant or not. "Constant" is defined
as "anything that doesn't involve actually looking in searched topics".
This function takes the same parameters (%domain) as evaluate(). Note that
no reference to the tom or data web or topic will be made, so you can
simply pass an arbitrary
Foswiki::Meta.
ObjectMethod
simplify(%opts)
Simplify the query by spotting constant expressions and evaluating them,
replacing the constant expression with an atomic value in the expression tree.
This function takes the same parameters (%domain) as evaluate(). Note that
no reference to the tom or data web or topic will be made, so you can
simply pass an arbitrary
Foswiki::Meta.
ObjectMethod
tokens() → []
Provided for compatibility with
Foswiki::Search::Node
ObjectMethod
isEmpty() → $boolean
Provided for compatibility with
Foswiki::Search::Node