Customize JPA field name mapping using EclipseLink

Question

I need to map camel-case names to underscore-separated names in my current project, which uses EclipseLink, due to historical reasons. I know we can customize name mapping i

Answer 1

In case you want to distinguish between non-annotated elements and annotated elements using @Column annotations, then I found a very beautiful example doing this:

public class CamelCaseSessionCustomizer implements SessionCustomizer {

@Override
public void customize(Session session) throws SQLException {
    for (ClassDescriptor descriptor : session.getDescriptors().values()) {
        // Only change the table name for non-embedable entities with no
        // @Table already
        if (!descriptor.getTables().isEmpty() && descriptor.getAlias().equalsIgnoreCase(descriptor.getTableName())) {
            String tableName = addUnderscores(descriptor.getTableName());
            descriptor.setTableName(tableName);
            for (IndexDefinition index : descriptor.getTables().get(0).getIndexes()) {
                index.setTargetTable(tableName);
            }
        }
        for (DatabaseMapping mapping : descriptor.getMappings()) {
            // Only change the column name for non-embedable entities with
            // no @Column already

            if (mapping instanceof AggregateObjectMapping) {
                for (Association association : ((AggregateObjectMapping) mapping).getAggregateToSourceFieldAssociations()) {
                    DatabaseField field = (DatabaseField) association.getValue();
                    field.setName(addUnderscores(field.getName()));

                    for (DatabaseMapping attrMapping : session.getDescriptor(((AggregateObjectMapping) mapping).getReferenceClass()).getMappings()) {
                        if (attrMapping.getAttributeName().equalsIgnoreCase((String) association.getKey())) {
                            ((AggregateObjectMapping) mapping).addFieldTranslation(field, addUnderscores(attrMapping.getAttributeName()));
                            ((AggregateObjectMapping) mapping).getAggregateToSourceFields().remove(association.getKey());
                            break;
                        }
                    }
                }
            } else if (mapping instanceof ObjectReferenceMapping) {
                for (DatabaseField foreignKey : ((ObjectReferenceMapping) mapping).getForeignKeyFields()) {
                    foreignKey.setName(addUnderscores(foreignKey.getName()));
                }
            } else if (mapping instanceof DirectMapMapping) {
                for (DatabaseField referenceKey : ((DirectMapMapping) mapping).getReferenceKeyFields()) {
                    referenceKey.setName(addUnderscores(referenceKey.getName()));
                }
                for (DatabaseField sourceKey : ((DirectMapMapping) mapping).getSourceKeyFields()) {
                    sourceKey.setName(addUnderscores(sourceKey.getName()));
                }
            } else {
                DatabaseField field = mapping.getField();
                if (field != null && !mapping.getAttributeName().isEmpty() && field.getName().equalsIgnoreCase(mapping.getAttributeName())) {
                    field.setName(addUnderscores(mapping.getAttributeName()));
                }
            }
        }
    }
}

private static String addUnderscores(String name) {
    if (name.equalsIgnoreCase("begintime")) {
        System.err.println();
    }
    StringBuffer buf = new StringBuffer(name.replace('.', '_'));
    for (int i = 1; i < buf.length() - 1; i++) {
        if (Character.isLowerCase(buf.charAt(i - 1)) && Character.isUpperCase(buf.charAt(i)) && Character.isLowerCase(buf.charAt(i + 1))) {
            buf.insert(i++, '_');
        }
    }
    return buf.toString().toLowerCase();
}

}

From https://gist.github.com/ganeshs/c0deb77ffae33dee4555