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Posted to dev@tinkerpop.apache.org by spmallette <gi...@git.apache.org> on 2016/08/03 22:57:52 UTC
[GitHub] tinkerpop pull request #371: Added new recipe for Traversal Induced Values.
GitHub user spmallette opened a pull request:
https://github.com/apache/tinkerpop/pull/371
Added new recipe for Traversal Induced Values.
Just a documentation addition. I learned that it's not so good to CTR these as there is sometimes good feedback on Gremlin code that should be incorporated and a PR is the best way to go about gathering that feedback.
VOTE +1
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/apache/tinkerpop TINKERPOP-1396
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/tinkerpop/pull/371.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #371
----
commit 8a59e48255ca9df3b547e66f00ec79fe1ab280a0
Author: Stephen Mallette <sp...@genoprime.com>
Date: 2016-08-03T22:54:28Z
Added new recipe for Traversal Induced Values.
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[GitHub] tinkerpop issue #371: Added new recipe for Traversal Induced Values.
Posted by spmallette <gi...@git.apache.org>.
Github user spmallette commented on the issue:
https://github.com/apache/tinkerpop/pull/371
Please ignore the failing test:
IdentityRemovalStrategyTest$PerformanceTest>TraversalStrategyPerformanceTest.shouldBeFaster:107 null
that's an issue raised elsewhere: https://issues.apache.org/jira/browse/TINKERPOP-1390
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[GitHub] tinkerpop issue #371: Added new recipe for Traversal Induced Values.
Posted by okram <gi...@git.apache.org>.
Github user okram commented on the issue:
https://github.com/apache/tinkerpop/pull/371
VOTE +1.
This got me to thinking that we really need to start to extend other steps (beyond the `Mutating`) to support traversal parameterization.
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[GitHub] tinkerpop pull request #371: Added new recipe for Traversal Induced Values.
Posted by asfgit <gi...@git.apache.org>.
Github user asfgit closed the pull request at:
https://github.com/apache/tinkerpop/pull/371
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[GitHub] tinkerpop pull request #371: Added new recipe for Traversal Induced Values.
Posted by pluradj <gi...@git.apache.org>.
Github user pluradj commented on a diff in the pull request:
https://github.com/apache/tinkerpop/pull/371#discussion_r73521595
--- Diff: docs/src/recipes/traversal-induced-values.asciidoc ---
@@ -0,0 +1,83 @@
+////
+Licensed to the Apache Software Foundation (ASF) under one or more
+contributor license agreements. See the NOTICE file distributed with
+this work for additional information regarding copyright ownership.
+The ASF licenses this file to You under the Apache License, Version 2.0
+(the "License"); you may not use this file except in compliance with
+the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+////
+[[traversal-induced-values]]
+Traversal Induced Values
+------------------------
+
+The parameters of a `Traversal` can be known ahead of time as constants or might otherwise be passed in as dynamic
+arguments.
+
+[gremlin-groovy,modern]
+----
+g.V().has('name','marko').out('knows').has('age', gt(29)).values('name')
+----
+
+In plain language, the above Gremlin asks, "What are the names of the people who Marko knows who are over the age of
+29?". In this case, "29" is known as a constant to the traversal. Of course, if the question is changed slightly to
+instead ask, "What are the names of the people who Marko knows who are older than he is?", the hardcoding of "29" will
+no longer suffice. There are multiple ways Gremlin would allow this second question to be answered. The first is
+obvious to any programmer - use a variable:
+
+[gremlin-groovy,modern]
+----
+marko = g.V().has('name','marko').next()
+g.V(marko).out('knows').has('age', gt(marko.value('age'))).values('name')
+----
+
+The downside to this approach is that it takes two separate traversals to answer the question. Ideally, there should
+be a single traversal, that can query "marko" once, determine his `age` and then use that for the value supplied to
+filter the people he knows. In this way the _value_ for the `age` filter is _induced_ from the `Traversal` itself.
+
+[gremlin-groovy,modern]
+----
+g.V().has('name','marko').as('marko'). <1>
+ out('knows').as('friend'). <2>
+ filter(select('marko','friend').by('age'). <3>
+ where('friend', gt('marko'))). <4>
+ values('name')
+----
+
+<1> Find the "marko" `Vertex` and label it as "marko".
+<2> Traverse out on the "knows" edges to the adjacent `Vertex` and label it as "person".
+<3> Filter the incoming "person" vertices. It is within this filter, that the traversal induced values are utilized.
+The inner `select` grabs the "marko" vertex and the current "friend". The `by` modulator extracts the "age" from both
+of those vertices which yields a `Map` with two keys, "marko" and "friend", where the value of each is the "age".
+<4> The `Map` produced in the previous step can then be filtered with `where` to only return a result if the "friend"
+age is greater than the "marko" age. If this is successful, then the `filter` step from the previous line will succeed
+and allow the "friend" vertex to pass through.
+
+This traversal could also be written declaratively with `match` step as follows:
--- End diff --
Should there be any discussion of the possible performance differences between the 2 approaches? Or is that mostly a system-specific discussion?
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[GitHub] tinkerpop pull request #371: Added new recipe for Traversal Induced Values.
Posted by spmallette <gi...@git.apache.org>.
Github user spmallette commented on a diff in the pull request:
https://github.com/apache/tinkerpop/pull/371#discussion_r73552034
--- Diff: docs/src/recipes/traversal-induced-values.asciidoc ---
@@ -0,0 +1,83 @@
+////
+Licensed to the Apache Software Foundation (ASF) under one or more
+contributor license agreements. See the NOTICE file distributed with
+this work for additional information regarding copyright ownership.
+The ASF licenses this file to You under the Apache License, Version 2.0
+(the "License"); you may not use this file except in compliance with
+the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+////
+[[traversal-induced-values]]
+Traversal Induced Values
+------------------------
+
+The parameters of a `Traversal` can be known ahead of time as constants or might otherwise be passed in as dynamic
+arguments.
+
+[gremlin-groovy,modern]
+----
+g.V().has('name','marko').out('knows').has('age', gt(29)).values('name')
+----
+
+In plain language, the above Gremlin asks, "What are the names of the people who Marko knows who are over the age of
+29?". In this case, "29" is known as a constant to the traversal. Of course, if the question is changed slightly to
+instead ask, "What are the names of the people who Marko knows who are older than he is?", the hardcoding of "29" will
+no longer suffice. There are multiple ways Gremlin would allow this second question to be answered. The first is
+obvious to any programmer - use a variable:
+
+[gremlin-groovy,modern]
+----
+marko = g.V().has('name','marko').next()
+g.V(marko).out('knows').has('age', gt(marko.value('age'))).values('name')
+----
+
+The downside to this approach is that it takes two separate traversals to answer the question. Ideally, there should
+be a single traversal, that can query "marko" once, determine his `age` and then use that for the value supplied to
+filter the people he knows. In this way the _value_ for the `age` filter is _induced_ from the `Traversal` itself.
+
+[gremlin-groovy,modern]
+----
+g.V().has('name','marko').as('marko'). <1>
+ out('knows').as('friend'). <2>
+ filter(select('marko','friend').by('age'). <3>
+ where('friend', gt('marko'))). <4>
+ values('name')
+----
+
+<1> Find the "marko" `Vertex` and label it as "marko".
+<2> Traverse out on the "knows" edges to the adjacent `Vertex` and label it as "person".
+<3> Filter the incoming "person" vertices. It is within this filter, that the traversal induced values are utilized.
+The inner `select` grabs the "marko" vertex and the current "friend". The `by` modulator extracts the "age" from both
+of those vertices which yields a `Map` with two keys, "marko" and "friend", where the value of each is the "age".
+<4> The `Map` produced in the previous step can then be filtered with `where` to only return a result if the "friend"
+age is greater than the "marko" age. If this is successful, then the `filter` step from the previous line will succeed
+and allow the "friend" vertex to pass through.
+
+This traversal could also be written declaratively with `match` step as follows:
--- End diff --
I thought about going into more detail there, but opted not to. I kinda thought that if we wanted that sort of content that it didn't belong in a recipe but in reference docs. It seemed a little out of scope of the recipe.
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[GitHub] tinkerpop issue #371: Added new recipe for Traversal Induced Values.
Posted by twilmes <gi...@git.apache.org>.
Github user twilmes commented on the issue:
https://github.com/apache/tinkerpop/pull/371
Looks good, nice choice for a recipe.
VOTE: +1
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[GitHub] tinkerpop issue #371: Added new recipe for Traversal Induced Values.
Posted by twilmes <gi...@git.apache.org>.
Github user twilmes commented on the issue:
https://github.com/apache/tinkerpop/pull/371
I might be missing something silly here, but It looks like you need to commit `traversal-induced-values.asciidoc`. I'm only seeing the updates to the changelog and index on this branch.
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[GitHub] tinkerpop issue #371: Added new recipe for Traversal Induced Values.
Posted by spmallette <gi...@git.apache.org>.
Github user spmallette commented on the issue:
https://github.com/apache/tinkerpop/pull/371
Sorry - forgot to add the file @twilmes - fixed up the commit and force pushed.
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