Break circular dependency between DataView and IDataProvider (size versus
offset/count)
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Key: WICKET-1784
URL: https://issues.apache.org/jira/browse/WICKET-1784
Project: Wicket
Issue Type: Improvement
Components: wicket
Affects Versions: 1.3.3
Environment: Wicket 1.3.3
Reporter: R. Goodwin
In some environments searches are performed in 'single call' fashion,
E.g. two queries performed by the data services tier before returning combined
results to the UI tier:
i. Query for paged search results
ii. Query for a 'count' value representing total possible results
The contract between DataView and IDataProvider does not support a 'single
call' environment as the give/take relationship between these classes is biased
towards DataView.
DataView expects IDataProvider to provide it's size before providing
IDataProvider with its offset and count.
* DataView may have good reasons for needing size before it can provide
offset/count.
* But IDataProvider has equally good reasons for needing offset/count before it
can provide size.
The circular dependency:
1. DataView calls IDataProvider.size()
2. IDataProvider cannot return size as it cannot start a query until it
receives offset/count from DataView
3. These it does not receive until DataView calls IDataProvider.iterator()
later on
Others who experienced this problem (with CODE examples):
* http://www.nabble.com/IDataProvider-and-Hibernate-Search-td15546101.html
* http://www.mail-archive.com/[EMAIL PROTECTED]/msg14266.html
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The suggested solution of caching the combined search results and count value
does not work if the search cannot begin until offset and count are available.
And writing a custom DataView is not feasible either time wise as I understand
that it cannot be done without needing to write a number of other classes too.
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