CODEWITHSUNDEEP
javagoogle-app-enginegoogle-cloud-datastore
Pokuri
Pokuri

Reputation: 3082

datastore index exception though I have defined index for the same

I have an entity king review as follows properties and value

Review {
 merchantId : 'X',
 appId : 'Y',
 productId : 'Z',
 reviewId : '12345',
 timeStamp : '1493482784728',
 viewtimestamp : '148834892374'
}

and I have defined index as follows

<datastore-index kind="review" ancestor="false" source="manual">
        <property name="merchantId" direction="asc"/>
        <property name="appId" direction="asc"/>
        <property name="productId" direction="asc"/>
        <property name="reviewId" direction="asc"/>
        <property name="timeStamp" direction="desc"/>
        <property name="viewtimestamp" direction="desc"/>
    </datastore-index>

And my query is as follows

SELECT reviewId FROM review WHERE merchantId = X AND appId = Y AND productId = Z;

When I execute this query I am getting following index sugession

<datastore-index kind="review" ancestor="false" source="manual">
    <property name="appId" direction="asc"/>
    <property name="merchantId" direction="asc"/>
    <property name="productId" direction="asc"/>
    <property name="reviewId" direction="asc"/>
</datastore-index>

Am I missing anything here? How the order get decided? Please help

Upvotes: 2

Views: 136

Answers (1)

Patrice
Patrice

Reputation: 4692

Indexes don't behave that way. If the system cannot find your precise index for the query, it won't return.

Having a more complex index and trying to serve your query with that index means that the datastore would need to do some calculations instead of a straight up lookup. And datastore doesn't do that.

If you want your queries to go through AT ALL, you need indexes for them, or it just won't run. The ONLY difference is the zigzag merge join algorithm that can help serve your queries if you DON'T have all the indexes. But you can't rely only on it, as it cannot serve everything, it needs partial indexes

Upvotes: 3

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