Mapping a FunctionalJava Option<Type> with Hibernate
-
09-06-2021 - |
سؤال
I have a hibernate-mapped Java object, JKL
, which is full of a bunch of normal hibernate-mappable fields (like strings and integers).
I'm added a new embedded field to it (which lives in the same table -- not a mapping), asdf
, which is a fj.data.Option<ASDF>
. I've made it an option to make it clear that this field may not actually contain anything (as opposed to having to handle null
every time I access it).
How do I set up the mapping in my JKL.hbm.xml
file? I'd like hibernate to automatically convert a null
in the database to a none
of fj.data.Option<ASDF>
when it retrieves the object. It should also convert a non-null instance of ASDF
to a some
of fj.data.Option<ASDF>
. Is there any other trickery that I have to do? Thank you.
المحلول
I would suggest introducing FunctionalJava's Option
in the accessors (getter and setter), while leaving Hibernate to handle a simple java field which is allowed to be null
.
For example, for an optional Integer
field:
// SQL
CREATE TABLE `JKL` (
`JKL_ID` INTEGER PRIMARY KEY,
`MY_FIELD` INTEGER DEFAULT NULL
)
You can map a Hibernate private field directly:
// Java
@Column(nullable = true)
private Integer myField;
You could then introduce Option
at the accessor boundary:
// Java
public fj.data.Option<Integer> getMyField() {
return fj.data.Option.fromNull(myField);
}
public void setMyField(fj.data.Option<Integer> value) {
myField = value.toNull();
}
Does that work for your needs?
نصائح أخرى
You can use Hibernate's custom mapping types. Documentation is here. Here is an analogous example of mapping Scala's Option to a Hibernate mapping.
Simply put, you would need to extend the org.hibernate.UserType
interface. You could also create a generic-typed base class with a JKL
-typed sub-type, similar to what you see in the Scala example.
I think using getter/setter
is simpler, but here's an example of what I did to make it work :
(It works fine for number and string, but not for date (error with @Temporal
annotation)).
import com.cestpasdur.helpers.PredicateHelper;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Optional;
import org.apache.commons.lang.ObjectUtils;
import org.apache.commons.lang.StringUtils;
import org.hibernate.HibernateException;
import org.hibernate.usertype.UserType;
import org.joda.time.DateTime;
import java.io.Serializable;
import java.sql.*;
public class OptionUserType implements UserType {
@Override
public int[] sqlTypes() {
return new int[]{
Types.NULL
};
}
@Override
public Class returnedClass() {
return Optional.class;
}
@Override
public boolean equals(Object o, Object o2) throws HibernateException {
return ObjectUtils.equals(o, o2);
}
@Override
public int hashCode(Object o) throws HibernateException {
assert (o != null);
return o.hashCode();
}
@Override
public Optional<? extends Object> nullSafeGet(ResultSet rs, String[] names, Object owner) throws HibernateException, SQLException {
return Optional.fromNullable(rs.getObject(names[0]));
}
@VisibleForTesting
void handleDate(PreparedStatement st, Date value, int index) throws SQLException {
st.setDate(index, value);
}
@VisibleForTesting
void handleNumber(PreparedStatement st, String stringValue, int index) throws SQLException {
Double doubleValue = Double.valueOf(stringValue);
st.setDouble(index, doubleValue);
}
@Override
public void nullSafeSet(PreparedStatement st, Object value, int index) throws SQLException {
if (value != null) {
if (value instanceof Optional) {
Optional optionalValue = (Optional) value;
if (optionalValue.isPresent()) {
String stringValue = String.valueOf(optionalValue.get());
if (StringUtils.isNotBlank(stringValue)) {
if (PredicateHelper.IS_DATE_PREDICATE.apply(stringValue)) {
handleDate(st, new Date(DateTime.parse(stringValue).getMillis()), index);
} else if (StringUtils.isNumeric(stringValue)) {
handleNumber(st, stringValue, index);
} else {
st.setString(index, optionalValue.get().toString());
}
} else {
st.setString(index, null);
}
} else {
System.out.println("else Some");
}
} else {
//TODO replace with Preconditions guava
throw new IllegalArgumentException(value + " is not implemented");
}
} else {
st.setString(index, null);
}
}
@Override
public Object deepCopy(Object o) throws HibernateException {
return o;
}
@Override
public boolean isMutable() {
return false;
}
@Override
public Serializable disassemble(Object o) throws HibernateException {
return (Serializable) o;
}
@Override
public Object assemble(Serializable serializable, Object o) throws HibernateException {
return serializable;
}
@Override
public Object replace(Object original, Object target, Object owner) throws HibernateException {
return original;
}
}