Project fields in queries

[sureshp31]

Is it possible to project fields, could not find any documentation related to this:

I want to project only the "id" and "name" fields from this query.

@EnableScan
public interface ProductInfoRepository extends
  CrudRepository<ProductInfo, String> {
     
    List<ProductInfo> findById(String id);
}

[astetsa]

List<ProductInfo> findByIdAndName(String id, String name);

[sureshp31]

@astetsa this is for querying based on id and name right?, i meant projection of fields in the returned result set. eg: if product_info has id,name,address,contact_details, i want the result set to have only id and name.

[astetsa]

So. You can implement two repositories. First is ProductInfo based. Second is ProductInfoShort based. First is used to save data. Second is used to find and return short data.

[derjust]

Yes that's the approach I'd also chose with two repositories.
You can derive ProductInfo from ProductInfoShort to not duplicate the annotations etc.

[sureshp31]

thanks got it. is it possible to have projections like its available in other spring data modules like mongo where we can pass the fields to be returned.

like in 2.2:
http://www.baeldung.com/spring-data-mongodb-projections-aggregations

[derjust]

Yes totally possible and easier than expected. An implementation would be similar to MongoDB via an projection-expression that is mapped from a @Query. To stick with the example from the AWS documentation that would look like this:

@Query(fields="Title") // comma separated list as per AWS documentation above
public List<ProductCatalog> findById(Long id);

which would load only the Title (and the key) attribute.

Might be also worth to look in parallel in addressing #78.

Possible workaround until then:

• Create a 'short' version of your object and have a second repository (as mentioned above)
• Create a GSI with projected attributes and create query method for that

[derjust]

Merged & will be available in 5.0.3

[sureshp31]

thanks a lot

[mr-goez]

The annotation seems not to work properly, I'm trying to declare fields, I want to have projected but when performing a GET-Request I get the JSON-Doc with just null values.
When I let the annotation without declaring any fields, it gives me only those that are in the method name and teh rest is null again.

Any suggestions?

[arthurhenning]

I'm also having issues with the @Query annotation used in combination with @EnableScan and findAll method. @derjust is this combination not supported?

`@DynamoDBTable(tableName = "vcc-globalprovisioning-PrimaryTenant-v1")
public class PrimaryTenant {

@Id
@DynamoDBHashKey
private String tenantId;

@DynamoDBIndexHashKey(globalSecondaryIndexName = "gsi-primaryTenant-customerId")
private String customerId;

@DynamoDBIndexHashKey(globalSecondaryIndexName = "gsi-primaryTenant-siteId")
private String siteId;

@DynamoDBIndexHashKey(globalSecondaryIndexName = "gsi-primaryTenant-clusterId")
private String clusterId;

@DynamoDBTypeConvertedEnum
private TenantSourceType source;

private String customerName;
private String pbxName;
private String parentAccountId;

private boolean isDRActivated;
private DRTenant drTenant;

}`

`public interface PrimaryTenantRepository extends DynamoDBCrudRepository<PrimaryTenant, String> {

@EnableScan
@EnableScanCount
@Query(fields = "tenantId,customerId,customerName")
Page<PrimaryTenant> findAll(Pageable pageable);

}`

Calling this method returns also other fields than the enumerated ones in the @Query.