JPA domain.Sort based on content of json column? - mysql

Question

I have a column defined as follows:
#Type(type = "json")
#Column(name = "ex_data")
#JsonProperty
#JsonTypeInfo(use = JsonTypeInfo.Id.CLASS)
private T exData;
Where, given type T, I can store a variety of basic JSON objects in my table, like so:
{
"active": true,
"color": "red",
"flavor": "cherry"
}
If I want to created a sorted, paginated, query against the table, is it possible to use the content of the JSON for the Sort object?
i.e. an equivalent to this, which presently does not work:
Sort sort = Sort.by("exData.color").ascending();

Answer 1

JSON is not directly supported by JPA.
One way would be to use a native SQL function to access a specific property nested inside the json column.
Unfortunately, native expressions are not supported when using Sort, which only accepts entity properties to order by.
Solution 1: native query with json key parameter and pagination
#Repository
public interface JsonSortNativeRepositoryMySql extends JpaRepository<JsonSortNativeEntity, Long> {
#Query(value = "SELECT * FROM json_sort_native_entity ORDER BY "
// flexibly extract the sort value from json:
+ "my_json_column->> :sortKey" //
+ " DESC", //
countQuery = "select count(*) from json_sort_native_entity", //
nativeQuery = true)
Page<JsonSortNativeEntity> findSortedNative(Pageable pageable, #Param("sortKey") String sortKey);
}
The corresponding pageable is created without Sort parameter, and the sort key can be dynamically supplied when calling the native query method:
var pageable = PageRequest.of(0, 20); // first page with 20 entries
var pageResult = repository.findSortedNative(pageable, "$.color");
Solution 2: sort by computed attribute value
Another option would be to specify a computed attribute value using a Hibernate #Formula as part of the Entity:
#Formula("my_json_column->>'$.color'") // <-- fixed key "color" to extract from json column
private String formulaValue;
This way, a normal Sort can be used:
var pageable = PageRequest.of(0, 20, Sort.by("formulaValue").descending());
var pageResult = repository.findAll(pageable); // standard JpaRepository method
However, the key to extract the sort values is fixed in this case (possible alternative: Spring Data - Page Request - order by function)
MySQL JSON reference: https://dev.mysql.com/doc/refman/8.0/en/json.html