How to return a List of Objects instead of Array of Objects from a Spring Data JPA GROUP BY query

Question

My question is related to this thread.

Following is my repository method using group by some field:

@Query(value = "SELECT  t.test_id AS testId, COUNT(t.id) AS total FROM test_instances t GROUP BY t.test_id", nativeQuery = true)
public Object[] getTestStats();

It's working and the result is obtained as follows:

[ [ 1, 2 ], [ 2, 1 ], [ 3, 2 ], [ 5, 1 ], [ 7, 2 ], [ 8, 1 ], [ 9, 1 ] ]

But, when I replace return type of getTestStats() from Object[] to List<?> I am getting the following error message:

{
"cause": null,
"message": "Couldn't find PersistentEntity for type class [Ljava.lang.Object;!"]
}

I want to use List<?> because if it is working, I want to use custom projection to cast it to i.e., List<CustomProjection>

I tried following return types {List<?>, List<CustomProjection>, CustomProjection[]}; but every thing is returning the same error. Hope someone will help me, thanks in advance.

Youcef LAIDANI · Accepted Answer · 2019-10-25 08:04:28Z

2

If you want to return a List then :

create a constructor which hold this fiels
in your query you can create an Object which took this fields.

For example :

 Select new com.CustomObject(t.test_id, COUNT(t.id))

And in this case you can use List<CustomObject> instead of an array of objects

answered Oct 25, 2019 at 8:04

Youcef LAIDANI

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13 Comments

Mohan Over a year ago

I tried this also but still, it causes the same error. Thanks for your answer.

Mohan Over a year ago

If I return only one record from the query using where clause then I can easily map that record to the CustomObject, but I am unable to do it while returning multiple records.

Youcef LAIDANI Over a year ago

This is a general solution, can you confirm that you example is the same as your real code?

Youcef LAIDANI Over a year ago

Can you please show me your code after edit ? And which version of spring boot you are using?

Emmanuel Ogoma Over a year ago

it should be public Object[][] getTestStats()

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