Getting column names from a JPA Native Query

Question

I have an administrative console in my web application that allows an admin to perform a custom SQL SELECT query on our database.

Underneath, the application is using Hibernate, but these queries are not HQL, they're pure SQL, so I'm using a Native Query like this:

protected EntityManager em;

public List<Object[]> execute(String query) {
    Query q = em.createNativeQuery(query);
    List<Object[]> result = q.getResultList();
    return result;
}

This works correctly, but it only returns the rows of data, with no extra information. What I would like is to also get the column names, so when I print the results back to the user I can also print a header to show what the various columns are.

Is there any way to do this?

Answer 1

2020

With hibernate 5.2.11.Final is actually pretty easy. In my example you can see how I get the column names for every row. And how I get values by column name.

Query q = em.createNativeQuery("SELECT columnA, columnB FROM table");
List<Tuple> result = q.getResultList();

for (Tuple row: result){

    // Get Column Names
    List<TupleElement<Object>> elements = row.getElements();
    for (TupleElement<Object> element : elements ) {
        System.out.println(element.getAlias());
    }

    // Get Objects by Column Name
    Object columnA;
    Object columnB;
    try {
        columnA = row.get("columnA");
        columnB= row.get("columnB");
    } catch (IllegalArgumentException e) {
        System.out.println("A column was not found");
    }
}

Answer 2

This code worked for me

DTO Class :

 public class ItemResponse<T> {

 private T item;

 public ItemResponse() {
 }

 public ItemResponse(T item) {
   super();
   this.item = item;
 }

 public T getItem() {
    return item;
}

public void setItem(T item) {
    this.item = item;
}

}

Service Class is in the below

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;
import org.springframework.stereotype.Service;
import org.hibernate.transform.AliasToEntityMapResultTransformer;

@Service
public class ServiceClass{ 

@PersistenceContext
public EntityManager entityManager;

public ItemResponse exceuteQueryResponse(String queryString) {

        ItemResponse itemResponse=new ItemResponse();           
        Query jpaQuery =  entityManager.createNativeQuery(queryString);
        org.hibernate.Query hibernateQuery =((org.hibernate.jpa.HibernateQuery)jpaQuery).getHibernateQuery();
      hibernateQuery.setResultTransformer(AliasToEntityMapResultTransformer.INSTANCE);
        List<Map<String,Object>> res = hibernateQuery.list();

        itemResponse.setItem(res);
        return itemResponse;

    }

    }

Answer 3

Ryiad's answer DTO adds some confusion, you should have kept it away. You should have explained that it works only with hibernate.

If like me you needs to keep the order of columns, you can specify your own transformer. i copied the code from hibernate and changed the HashMap to LinkedHashMap:

import java.util.LinkedHashMap;
import java.util.Map;

import org.hibernate.transform.AliasedTupleSubsetResultTransformer;
import org.hibernate.transform.ResultTransformer;

/**
 * {@link ResultTransformer} implementation which builds a map for each "row", made up of each aliased value where the
 * alias is the map key. Inspired by {@link org.hibernate.transform.AliasToEntityMapResultTransformer}, but kepping the
 * ordering of elements.
 * <p/>
 * Since this transformer is stateless, all instances would be considered equal. So for optimization purposes we limit
 * it to a single, singleton {@link #INSTANCE instance}.
 */
public class AliasToEntityMapResultTransformer extends AliasedTupleSubsetResultTransformer {

    public static final AliasToEntityMapResultTransformer INSTANCE = new AliasToEntityMapResultTransformer();

    /**
     * Disallow instantiation of AliasToEntityMapResultTransformer.
     */
    private AliasToEntityMapResultTransformer() {
    }

    @Override
    public Object transformTuple(Object[] tuple, String[] aliases) {
        Map result = new LinkedHashMap<>(tuple.length);
        for (int i = 0; i < tuple.length; i++) {
            String alias = aliases[i];
            if (alias != null) {
                result.put(alias, tuple[i]);
            }
        }
        return result;
    }

    @Override
    public boolean isTransformedValueATupleElement(String[] aliases, int tupleLength) {
        return false;
    }

    /**
     * Serialization hook for ensuring singleton uniqueing.
     *
     * @return The singleton instance : {@link #INSTANCE}
     */
    private Object readResolve() {
        return INSTANCE;
    }
}

With this transformer you can used Ryiad's solution with Hibernate:

    Query jpaQuery =  entityManager.createNativeQuery(queryString);
    org.hibernate.Query hibernateQuery =((org.hibernate.jpa.HibernateQuery)jpaQuery).getHibernateQuery();
  hibernateQuery.setResultTransformer(AliasToEntityMapResultTransformer.INSTANCE);
    List<Map<String,Object>> res = hibernateQuery.list();

Answer 4

如果 JPA 提供程序不支持查询元数据的检索，另一种解决方案可能是使用 SQL 解析器，如JSQLParser 、 ZQL或General SQL Parser （商业），它从SELECT语句中提取字段。

Answer 5

很长时间没有任何答案，并且根据我自己的进一步研究，似乎不可能，不幸的是。

Answer 6

cast query to hibernate query, then use hibernate method

          //normal use, javax.persistence.Query interface
    Query dbQuery = entityManager.createNativeQuery(sql);
    //cast to hibernate query
    org.hibernate.Query hibernateQuery =((org.hibernate.jpa.HibernateQuery)dbQuery)
            .getHibernateQuery();
    hibernateQuery.setResultTransformer(AliasToEntityMapResultTransformer.INSTANCE);

    List<Map<String,Object>> res = hibernateQuery.list();

    List<TxTestModel> txTestModels = new ArrayList<>();
    res.forEach(e->{
        TxTestModel txTestModel = new ObjectMapper().convertValue(e, TxTestModel.class);
    //  txTestModels.add(new TxTestModel().setIdd((Integer) e.get("idd")).setMmm((String) e.get("mmm")).setDdd((Date) e.get("ddd")));
        txTestModels.add(txTestModel);
    });
    System.out.println(txTestModels.size());

Answer 7

To enforce em.createNativeQuery(..).getResultList() to return List<Tuple> specify it with Tuple.class when creating native queries :

Query q = em.createNativeQuery("SELECT columnA, columnB FROM table", Tuple.class );

List<Tuple> result = q.getResultList();

for (Tuple row: result){

    // Get Column Names
    List<TupleElement<Object>> elements = row.getElements();
    for (TupleElement<Object> element : elements ) {
        System.out.println(element.getAlias());
    }

    // Get Objects by Column Name
    Object columnA;
    Object columnB;
    try {
        columnA = row.get("columnA");
        columnB= row.get("columnB");
    } catch (IllegalArgumentException e) {
        System.out.println("A column was not found");
    }

}

Answer 8

Query query = entityManager.createNamedQuery(namedQuery);
NativeQueryImpl nativeQuery = (NativeQueryImpl) query;
nativeQuery.setResultTransformer(AliasToEntityMapResultTransformer.INSTANCE);
List<Map<String,Object>> result = nativeQuery.getResultList();

And now you have Map<String,Object> . You can see your Column Names

Answer 9

This worked for me:

    final Query emQuery = em.createNativeQuery(query, Tuple.class);
    final List<Tuple> queryRows = emQuery.getResultList();

    final List<Map<String, Object>> formattedRows = new ArrayList<>();

    queryRows.forEach(row -> {
        final Map<String, Object> formattedRow = new HashMap<>();

        row.getElements().forEach(column -> {
            final String columnName = column.getAlias();
            final Object columnValue = row.get(column);

            formattedRow.put(columnName, columnValue);
        });
        
        formattedRows.add(formattedRow);
    });

    return formattedRows;

Answer 10

List dataList = session.createSQLQuery("SLECT * FROM EMPLOYEETABLE").setResultTransformer(Transformers.ALIAS_TO_ENTITY_MAP).list();
for (Object obj : dataList) {
    HashMap<String, Object> hashMap = (HashMap<String, Object>) obj;
    Set<String> keySet = hashMap.keySet();
    break;
}

Answer 11

I also faced a similar problem working with JPA. There is no direct way in JPA to access the resultset metadata. The solution can be extracting column names from the query itself or use JDBC to get the metadata.