retrieving data via key in java

[Giridhar Kannan]

hi all,
i would like to know how to use the query

<b>" select __key__ from Class-Name "</b> in java .
The same syntax is not working, it shows the following
<b> PrimaryExpression should be a VariableExpression with name
__key__ </b>
Please do help me.

Thank you.

[Ikai L (Google)]

JDOQL isn't SQL, so I'm not surprised that this isn't working. It's not possible to retrieve only parts of an entity, so this syntax wouldn't have made a whole lot of sense. An alternate method of doing a Key only query is to use the low-level API:

http://code.google.com/appengine/docs/java/javadoc/com/google/appengine/api/datastore/Query.html#setKeysOnly()

When you form a query, set it to Keys only rather than retrieving complete entities. What this mean is that this only hits your indexes, returning the subset of keys that match. You can then use these Keys as you would normally use them.

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Ikai Lan
Developer Programs Engineer, Google App Engine