Do you ever have criteria to your query? If so, I think you need both
indexes because below is the way that I think of queries working. I'm not
sure if it's true - maybe a Googler could let us know if this is about
right or wildly wrong?
Use ascending index to find the first entity with the value required.
Use descending index to find the last entity with the value required.
Return all entity keys between the first and the last.
If not a keys-only query - fetch the entities using a batch get.
If this is the way it works, I wouldn't be surprised if Google have set it
up to require both indexes because they would be required in all uses
(because it would probably be just as quick to do sorting in memory if you
fetch all entities).
Thanks,
Mat.
On 3 February 2012 02:04, Bruno Fuster <brunofus...@gmail.com> wrote:
> I'm not sure but maybe JDO is trying to query asceding to fetch the
> children before adding.
>
>
>
>
>
>
> On Thu, Feb 2, 2012 at 9:36 PM, Miguel <doctormig...@gmail.com> wrote:
>
>> Hi,
>> I am working on a simple structure similar to:
>>
>> class Parent {
>> ...
>> List<Child> children
>> ..
>> }
>>
>> class Child {
>> ..
>> Parent parent
>> ..
>> }
>>
>> mapped with a 1-N relation in JDO:
>> <field persistence-modifier="persistent" name="children" mapped-
>> by="parent">
>> <collection dependent-element="true" element-type="Child"></
>> collection>
>> <order/>
>> </field>
>>
>>
>> with a simple index:
>> <datastore-index kind="Child" ancestor="true" source="manual">
>> <property name="children_INTEGER_IDX" direction="desc"/>
>> </datastore-index>
>>
>> .. and I always retrieve Children in descending order.
>>
>> But when I add a children I get this error:
>> com.google.appengine.api.datastore.DatastoreNeedIndexException: no
>> matching index found.
>> The suggested index for this query is:
>> <datastore-index kind="Child" ancestor="true" source="manual">
>> <property name="children_INTEGER_IDX" direction="asc"/>
>> </datastore-index>
>>
>> So my question is: why do I always need both indexes for ascending and
>> descending order if I need only type of ordering?
>>
>> Thanks,
>> Michele
>>
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>
>
> --
> Bruno Fuster
>
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