public interface Scoping
Step implementations that access labeled path steps, side-effects or
Map values by key, such as select('a') step. Note that a step like project() is non-scoping
because while it creates a Map it does not introspect them.
There are four types of scopes:
traverser.get()
object. Another way to think about the current scope is to think in terms of the path of the traverser where the
current scope is the head of the path. With the math()-step, the variable _ refers to the current scope.
gremlin> g.V().values("age").math("sin _")
==>-0.6636338842129675
==>0.956375928404503
==>0.5514266812416906
==>-0.428182669496151
The path scope refers to data previously seen by the traverser. That is, data in the traverser’s path history.
Paths can be accessed by path(), however, individual parts of the path can be labeled using as()
and accessed later via the path label name. Thus, in the traversal below, “a” and “b” refer to objects previously
traversed by the traverser.
gremlin> g.V().as("a").out("knows").as("b”).
math("a / b").by("age")
==>1.0740740740740742
==>0.90625
The side-effect scope refers objects in the global side-effects of the traversal. Side-effects are not local to the
traverser, but instead, global to the traversal. In the traversal below you can see how “x” is being referenced in
the math()-step and thus, the side-effect data is being used.
gremlin> g.withSideEffect("x",100).V().values("age").math("_ / x")
==>0.29
==>0.27
==>0.32
==>0.35
Map scope refers to objects within the current map object. Thus, its like current scope, but a bit “deeper.” In the
traversal below the project()-step generates a map with keys “a” and “b”. The subsequent math()-step
is then able to access the “a” and “b” values in the respective map and use them for the division operation.
gremlin>
g.V().hasLabel("person”).
project("a","b”).
by("age”).
by(bothE().count()).
math("a / b")
==>9.666666666666666
==>27.0
==>10.666666666666666
==>35.0
Scoping is all about variable data access and forms the fundamental interface for access to the memory structures
of Gremlin.| Modifier and Type | Interface and Description |
|---|---|
static class |
Scoping.KeyNotFoundException |
static class |
Scoping.Variable |
| Modifier and Type | Method and Description |
|---|---|
default <S> S |
getNullableScopeValue(Pop pop,
String key,
Traverser.Admin<?> traverser)
Calls
getScopeValue(Pop, Object, Traverser.Admin) and returns null if the key is not found. |
default <S> S |
getSafeScopeValue(Pop pop,
Object key,
Traverser.Admin<?> traverser)
Calls
getScopeValue(Pop, Object, Traverser.Admin) but throws an unchecked IllegalStateException
if the key cannot be found. |
Set<String> |
getScopeKeys()
Get the labels that this scoping step will access during the traversal
|
default <S> S |
getScopeValue(Pop pop,
Object key,
Traverser.Admin<?> traverser)
Finds the object with the specified key for the current traverser and throws an exception if the key cannot
be found.
|
default <S> S getScopeValue(Pop pop, Object key, Traverser.Admin<?> traverser) throws Scoping.KeyNotFoundException
Scoping.KeyNotFoundException - if the key does not existdefault <S> S getSafeScopeValue(Pop pop, Object key, Traverser.Admin<?> traverser)
getScopeValue(Pop, Object, Traverser.Admin) but throws an unchecked IllegalStateException
if the key cannot be found.default <S> S getNullableScopeValue(Pop pop, String key, Traverser.Admin<?> traverser)
getScopeValue(Pop, Object, Traverser.Admin) and returns null if the key is not found.
Use this method with caution as null has one of two meanings as a return value. It could be that the
key was found and its value was null or it might mean that the key was not found and null was
simply returned.Copyright © 2013–2021 Apache Software Foundation. All rights reserved.