15 replies

Extracting the ProjectStep of a GraphTraversal instance during unit testing

Tl;dr
Given an instance of

GraphTraversal<?, Map<String, Object>>

GraphTraversal<?, Map<String, Object>>

, is it possible to extract the

ProjectStep<?>

ProjectStep<?>

which is producing the

Map<String, Object>

Map<String, Object>

inferred by the type system, and which would be returned once a terminal step is applied?

We only want to access the

.projectKeys()

.projectKeys()

of the

ProjectStep

ProjectStep

, so we don't need to actually execute the traversal. It can be assumed that we are always dealing with an instance of

GraphTraversal<?, Map<String, Object>>

GraphTraversal<?, Map<String, Object>>

, and we do not have access to the actual graph in this environment.

Context
We have a system written in Java that defines Gremlin traversals to be run against a TinkerPop graph (Neptune, but not relevant for this question). These queries should be written such that they should return

Map<String, Object>

Map<String, Object>

(i.e. using

project()

project()

) with a specific set of keys which are defined alongside the query. We aren't yet using a custom DSL, and building queries programmatically to ensure the project step is present causes other problems.

Why are we doing this?
We'd like to give immediate (build-time) feedback to developers that the query they've written is missing an important key, which would otherwise take a deployment and some waiting time to discover. This key must be present, as the query will be executed by an automated system later which will try to extract a value from the

Map

Map

containing that same key.

What have we tried so far?
We've actually managed to do this using the mock example here to capture

project

project

steps, and recursively capture any which might include a

ProjectStep

ProjectStep

: https://github.com/apache/tinkerpop/blob/0c382bb7ec345f2758bee207d62d66f95c475a78/gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversalSourceTest.java#L107-L153

We've accomplished this by matching against the invoked method of the mocked

GraphTraversal

GraphTraversal

to detect either calls to

project

project

method directly, or to

TraversalParent

TraversalParent

steps which may contain child steps (like

local

local

) and from there recursively check all steps in search of a

project

project

. At that point, we can gather the

projectKeys

projectKeys

of the

ProjectStep

ProjectStep

. Happy to share some snippets of this if you're curious.

However, our implementation identifies any usage of

project

project

anywhere in the query, not necessarily the final one that will be returned by the server once a terminating step is applied.. It's technically 'good enough' as it will always catch cases where the required key is never mentioned in the traversal, but it's possible the query uses multiple projects, and the required key is misplaced and won't be part of the final map returned when executed.

Thoughts
In theory, I'm thinking this must be possible, since as soon as you use

project

project

in a traversal, Java is smart enough to understand that you are now working with a

GraphTraversal<?, Map<String, Object>>

GraphTraversal<?, Map<String, Object>>

. This might sometimes happen inside a

TraversalParent

TraversalParent

local()

local()

, but the type system can still infer it will receive a

Map

Map

when terminated. Is there a method (or collection of methods) which would let us grab the 'last effective step' which returns that

Map

Map

? The solution can be hacky, this is test-case code so there's room for some jank here

Thanks, folks!

Apache TinkerPop•3y ago•

15 replies

jessea

Extracting the ProjectStep of a GraphTraversal instance during unit testing

Tl;dr
Given an instance of

GraphTraversal<?, Map<String, Object>>

GraphTraversal<?, Map<String, Object>>

, is it possible to extract the

ProjectStep<?>

ProjectStep<?>

which is producing the

Map<String, Object>

Map<String, Object>

inferred by the type system, and which would be returned once a terminal step is applied?

We only want to access the

.projectKeys()

.projectKeys()

of the

ProjectStep

ProjectStep

, so we don't need to actually execute the traversal. It can be assumed that we are always dealing with an instance of

GraphTraversal<?, Map<String, Object>>

GraphTraversal<?, Map<String, Object>>

Map<String, Object>

Map<String, Object>

(i.e. using

project()

project()

Map

Map

containing that same key.

What have we tried so far?
We've actually managed to do this using the mock example here to capture

project

project

steps, and recursively capture any which might include a

ProjectStep

ProjectStep

GraphTraversal

GraphTraversal

to detect either calls to

project

project

method directly, or to

TraversalParent

TraversalParent

steps which may contain child steps (like

local

local

) and from there recursively check all steps in search of a

project

project

. At that point, we can gather the

projectKeys

projectKeys

of the

ProjectStep

ProjectStep

. Happy to share some snippets of this if you're curious.

However, our implementation identifies any usage of

project

project

project

project

in a traversal, Java is smart enough to understand that you are now working with a

GraphTraversal<?, Map<String, Object>>

GraphTraversal<?, Map<String, Object>>

. This might sometimes happen inside a

TraversalParent

TraversalParent

local()

local()

, but the type system can still infer it will receive a

Map

Map

when terminated. Is there a method (or collection of methods) which would let us grab the 'last effective step' which returns that

Map

Map

? The solution can be hacky, this is test-case code so there's room for some jank here

Thanks, folks!

Extracting the ProjectStep of a GraphTraversal instance during unit testing

Extracting the ProjectStep of a GraphTraversal instance during unit testing

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