Hello there,
I am not really sure if the following is an issue or just a lack of understanding on my side. I have two documents and try to find elements from one based on (attribute-stored) constraints given in the other. A basic example structure looks as follows:
<commands> <create-db name='test1'/> <add path='doc_a'><a><a1 id='1'/><b1 ref='1'/></a></add> <add path='doc_b'><b><b1 ref='1'/></b></add> </commands>
Queries: //a1[@id=//a/b1/@ref] => 1 hit
//a1[@id=//b/b1/@ref] => no hits?
When putting the nodes in one and the same document (adding a common parental node), either query returns 1 hit:
<commands> <create-db name='test2'/> <add path='doc'><any><a><a1 id='1'/><b1 ref='1'/></a><b><b1 ref='1'/></b></any></add> </commands>
What I would have expected is 1 hit in any of the cases, but finding the correct context in predicate expressions confused me more than one time...
Regards, Simon (BaseX Version is 7.8 beta 8f51466)
Hi Simon,
thanks for your mail. The reason for the surprising query result is that the root expression ("/") points to the document node of the node which is in the current context. In your query, this is the first document ("doc_a"):
//a1[@id = /......
I agree that the result is somewhat surprising, because you would possibly expect "/" to return all documents of your collection.
The following query will return the expected results (and it will usually be evaluated faster if you have indexed your documents):
let $refs := //b/b1/@ref return //a1[@id = $refs]
In this case, "/" is applied to all nodes in your initial context. As you are starting with the document nodes anyway, the following query would be equivalent:
let $refs := descendant::b/b1/@ref return descendant::a1[@id = $refs]
Hope this helps; feel free to ask for more details, Christian ________________________________
On Tue, Feb 11, 2014 at 6:58 PM, Simon Görke simon.goerke@ils.uni-stuttgart.de wrote:
Hello there,
I am not really sure if the following is an issue or just a lack of understanding on my side. I have two documents and try to find elements from one based on (attribute-stored) constraints given in the other. A basic example structure looks as follows:
<commands> <create-db name='test1'/> <add path='doc_a'><a><a1 id='1'/><b1 ref='1'/></a></add> <add path='doc_b'><b><b1 ref='1'/></b></add> </commands>
Queries: //a1[@id=//a/b1/@ref] => 1 hit
//a1[@id=//b/b1/@ref] => no hits?
When putting the nodes in one and the same document (adding a common parental node), either query returns 1 hit:
<commands> <create-db name='test2'/> <add path='doc'><any><a><a1 id='1'/><b1 ref='1'/></a><b><b1 ref='1'/></b></any></add> </commands>
What I would have expected is 1 hit in any of the cases, but finding the correct context in predicate expressions confused me more than one time...
Regards, Simon (BaseX Version is 7.8 beta 8f51466)
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Simon Görke