Parse string as json array from Postgre - json

Question

I have a table in PostgreSQL with 2 columns - Id and coord.
Column "coord" - geo coordinates stored as a string in JSON format.
Example:
[{"lat":49.09693425316379,"lng":33.61747393628419},{"lat":49.11835977646441,"lng":33.638456496907},{"lat":49.12103137811804,"lng":33.63866144845382},{"lat":49.09694682809236,"lng":33.61746879914138},{"lat":49.08920750204137,"lng":33.61734796797724},{"lat":49.07643862058337,"lng":33.61246117651179}]
How to send such string as JSON Array of objects(POST request).
Entity without getters and setters
public class Lepcoord implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#Basic(optional = false)
#NotNull
#Size(min = 1, max = 30)
#Column(name = "tplnr")
private String tplnr;
#Size(max = 2147483647)
#Column(name = "coord")
private String coord;
Controller
#POST
#RequestMapping(value= "/lep/{voltage}", method = RequestMethod.POST, headers = "Accept=application/json")
#ResponseBody
public ResponseEntity<List<Lepcoord>> lep (#PathVariable String voltage)
{
return new ResponseEntity<>(gisDaoService.lep(voltage), HttpStatus.OK);
}
And service
#Transactional(readOnly = true)
public List <Lepcoord> lep (String voltage) {
Query query = this.em.createQuery(
" From Lepcoord ");
List <Lepcoord> rez = null;
try {
rez = (List<Lepcoord>) query.getResultList();
} catch (PersistenceException r) {
return null;
}
return rez;
}
Hibernate cant handle json type If i storeing coord as json in Postgre. May be someone knows easier way. Not to write own classes to work with Postgres json type

Answer 1

You are using Hibernate so it is good to use a custom UserType which knows how to handle json.
create a hibernate usertype
public class GeoJsonType implements UserType
{
protected static final int[] SQL_TYPES = { java.sql.Types.VARCHAR };
#Override
public int[] sqlTypes()
{
return SQL_TYPES;
}
#Override
public Class returnedClass()
{
return GeoEntity.class;
}
#Override
public boolean equals(Object x, Object y) throws HibernateException
{
if (x == y)
{
return true;
}
else if (x == null || y == null)
{
return false;
}
else
{
return x.equals(y);
}
}
#Override
public int hashCode(Object x) throws HibernateException
{
return x.hashCode();
}
#Override
public Object nullSafeGet(ResultSet rs, String[] names, Object owner) throws HibernateException, SQLException
{
// if (rs.wasNull())
// {
// return null;
// }
//this is your json stored in db
String rsArr = rs.getString(names[0]);
if (rsArr == null)
return null;
GeoEntity detailAttr = JSON.toObject(rsArr, GeoEntity.class, null);
return detailAttr;
}
#Override
public void nullSafeSet(PreparedStatement st, Object value, int index) throws HibernateException, SQLException
{
if (value == null)
{
st.setNull(index, SQL_TYPES[0]);
}
else
{
//when stroing object into db convert it to json
GeoEntity castObject = (GeoEntity) value;
String json = JSON.toJson(castObject);
st.setString(index, json);
}
}
#Override
public Object deepCopy(Object value) throws HibernateException
{
return value;
}
#Override
public boolean isMutable()
{
return true;
}
#Override
public Serializable disassemble(Object value) throws HibernateException
{
return null;
}
#Override
public Object assemble(Serializable cached, Object owner) throws HibernateException
{
return null;
}
#Override
public Object replace(Object original, Object target, Object owner) throws HibernateException
{
return original;
}
}
Your Entity.java
#Type(type = "FQN to your GeoJsonType")
#Column(name = "geo")
public GeoEntity getGeo()
{
return geo;
}

Answer 2

Postgres supports the json_to_array function that should be of help here. Take a look at the documentation here.
Alternatively, there is this answer on SO: How to turn a json array into rows in postgres that could point you in the right direction.