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

Perhaps you could use my session customizer. It converts table names, and field names to Camel case. It supports inheritance and embeded entities. I tested for 2 years, and I got no issues or side effects. Enjoy it!

import java.sql.SQLException;
import java.util.Locale;
import java.util.Vector;
import org.eclipse.persistence.config.SessionCustomizer;
import org.eclipse.persistence.descriptors.ClassDescriptor;
import org.eclipse.persistence.internal.helper.DatabaseField;
import org.eclipse.persistence.mappings.DatabaseMapping;
import org.eclipse.persistence.sessions.Session;
import org.eclipse.persistence.tools.schemaframework.IndexDefinition;

public class CamelNamingStrategy implements SessionCustomizer {
    public static String unqualify(final String qualifiedName) {
        int loc = qualifiedName.lastIndexOf(".");
        return loc < 0 ? qualifiedName : qualifiedName.substring(qualifiedName.lastIndexOf(".") + 1);
    }

    @Override
    public void customize(final Session session) throws SQLException {
        for (ClassDescriptor descriptor : session.getDescriptors().values()) {
            if (!descriptor.getTables().isEmpty()) {
                // Take table name from @Table if exists
                String tableName = null;
                if (descriptor.getAlias().equalsIgnoreCase(descriptor.getTableName())) {
                    tableName = unqualify(descriptor.getJavaClassName());
                } else {
                    tableName = descriptor.getTableName();
                }
                tableName = camelCaseToUnderscore(tableName);
                descriptor.setTableName(tableName);
                for (IndexDefinition index : descriptor.getTables().get(0).getIndexes()) {
                    index.setTargetTable(tableName);
                }
                Vector mappings = descriptor.getMappings();
                camelCaseToUnderscore(mappings);
            } else if (descriptor.isAggregateDescriptor() || descriptor.isChildDescriptor()) {
                camelCaseToUnderscore(descriptor.getMappings());
            }
        }
    }

    private void camelCaseToUnderscore(Vector mappings) {
        for (DatabaseMapping mapping : mappings) {
            DatabaseField field = mapping.getField();
            if (mapping.isDirectToFieldMapping() && !mapping.isPrimaryKeyMapping()) {
                String attributeName = mapping.getAttributeName();
                String underScoredFieldName = camelCaseToUnderscore(attributeName);
                field.setName(underScoredFieldName);
            }
        }
    }

    private String camelCaseToUnderscore(final String name) {
        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(Locale.ENGLISH);
    }
}