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https://issues.apache.org/jira/browse/TINKERPOP-848?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17427118#comment-17427118
 ] 

ASF GitHub Bot commented on TINKERPOP-848:
------------------------------------------

spmallette commented on a change in pull request #1485:
URL: https://github.com/apache/tinkerpop/pull/1485#discussion_r726101651



##########
File path: 
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/graphml/GraphMLReader.java
##########
@@ -138,9 +143,11 @@ public void readGraph(final InputStream graphInputStream, 
final Graph graphToWri
                         case GraphMLTokens.DATA:
                             final String key = reader.getAttributeValue(null, 
GraphMLTokens.KEY);
                             final String dataAttributeName = keyIdMap.get(key);
+                            final String defaultValue = defaultValues.get(key);
 
                             if (dataAttributeName != null) {
-                                final String value = reader.getElementText();
+                                String elementValue =  reader.getElementText();
+                                final String value = elementValue.length() == 
0 && defaultValue.length() != 0 ? defaultValue : elementValue;

Review comment:
       I don't recall how `getElementText()` works. If you have `<data 
key="d_n"/>` does that return an empty string or `null`? If it's the former, 
which your code seems to indicate, doesn't this mean that GraphML can't have 
empty strings as values anymore (which may be what the user wants)? I think the 
point of the default specification is to deal with a situation like:
   
   ```xml
   <key id="d_n" for="node" attr.name="modification" attr.type="string">
     <default>add</default>
   </key>
   ...
   <node id="6315"></node>
   ```
   
   where the "modification" is not present at all for the `<node><data>` in 
which case it would include the default property of "modification" with an 
"add" value. otoh, if it were the following:
   
   ```xml
   <key id="d_n" for="node" attr.name="modification" attr.type="string">
     <default>add</default>
   </key>
   ...
   <node id="6315">
     <data key="modification"/>
   </node>
   ```
   
   it would just include the "modification" property with an empty string. Does 
that make sense?




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> Support default attribute values in GraphMLReader
> -------------------------------------------------
>
>                 Key: TINKERPOP-848
>                 URL: https://issues.apache.org/jira/browse/TINKERPOP-848
>             Project: TinkerPop
>          Issue Type: Improvement
>          Components: io
>    Affects Versions: 3.0.2-incubating
>            Reporter: Pavel Klinov
>            Priority: Trivial
>   Original Estimate: 2h
>  Remaining Estimate: 2h
>
> Looking at the code of GraphMLReader I see that it doesn't support default 
> values of attributes, which are allowed by the GraphML spec. This is a bit 
> annoying especially if the input defines default values for attributes which 
> are used for mandatory data, e.g. edge labels. 
> One small example is the sample graph at [1]. "d_e" is the label attribute 
> with a default value. There're <edge .. /> elements w/o body later in the 
> document and reading those will throw a "java.lang.IllegalArgumentException: 
> Label can not be null" exception (if the vendor considers edge labels 
> mandatory).
> I'd personaly squash both keyIdMap and keyTypesMap into a single String -> 
> AttrInfo map, where AttrInfo would contain information about the data 
> attribute name, type, and the default value.
> [1] http://www.eecs.wsu.edu/~yyao/DirectedStudyI/Datasets/AS/sample.graphml



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