我有一个 Converter 转换 String 在数据库中存储到相应的 Enum 要素：

@Converter(autoApply=true)
public class DokumentTypConverter implements AttributeConverter<DokumentTypSchluessel, String> {
   @Override
   public String convertToDatabaseColumn(DokumentTypSchluessel attribute) {
      return attribute.getValue();
   }
   @Override
   public DokumentTypSchluessel convertToEntityAttribute(String dbData) {
      return DokumentTypSchluessel.from(dbData);
   }
}

我有一个实体类，它有一个枚举类型的字段：

@Entity
@Table(name="REF_DOKUMENTTYPEN")
public class DokumentTyp {
   private DokumentTypSchluessel schluessel;
   // snip
}

现在，当我尝试从数据库中检索该实体的示例时

String query = "SELECT d FROM DokumentTyp d WHERE d.schluessel = " + VORBEREITUNG;
entityManager.createQuery(query, DokumentTyp.class).getSingleResult();

我得到以下错误：

javax.persistence.PersistenceException: An exception occurred while calling convertToDatabaseColumn on converter class de.drvbund.pub.model.convert.DokumentTypConverter with value VORBEREITUNG
        at org.eclipse.persistence.mappings.converters.ConverterClass.convertObjectValueToDataValue(ConverterClass.java:139)
        at org.eclipse.persistence.mappings.foundation.AbstractDirectMapping.getFieldValue(AbstractDirectMapping.java:778)
        at org.eclipse.persistence.internal.expressions.QueryKeyExpression.getFieldValue(QueryKeyExpression.java:420)
        at org.eclipse.persistence.internal.expressions.ConstantExpression.printSQL(ConstantExpression.java:152)
        at org.eclipse.persistence.expressions.ExpressionOperator.printDuo(ExpressionOperator.java:2241)
        at org.eclipse.persistence.internal.expressions.CompoundExpression.printSQL(CompoundExpression.java:286)
        at org.eclipse.persistence.internal.expressions.RelationExpression.printSQL(RelationExpression.java:899)
        at org.eclipse.persistence.internal.expressions.ExpressionSQLPrinter.translateExpression(ExpressionSQLPrinter.java:325)
        at org.eclipse.persistence.internal.expressions.ExpressionSQLPrinter.printExpression(ExpressionSQLPrinter.java:129)
        at org.eclipse.persistence.internal.expressions.SQLSelectStatement.printSQL(SQLSelectStatement.java:1755)
        at org.eclipse.persistence.internal.databaseaccess.DatabasePlatform.printSQLSelectStatement(DatabasePlatform.java:3268)
        at org.eclipse.persistence.platform.database.OraclePlatform.printSQLSelectStatement(OraclePlatform.java:967)
        at org.eclipse.persistence.internal.expressions.SQLSelectStatement.buildCall(SQLSelectStatement.java:843)
        at org.eclipse.persistence.internal.expressions.SQLSelectStatement.buildCall(SQLSelectStatement.java:854)
        at org.eclipse.persistence.descriptors.ClassDescriptor.buildCallFromStatement(ClassDescriptor.java:815)
        at org.eclipse.persistence.internal.queries.StatementQueryMechanism.setCallFromStatement(StatementQueryMechanism.java:390)
        at org.eclipse.persistence.internal.queries.StatementQueryMechanism.prepareSelectAllRows(StatementQueryMechanism.java:315)
        at org.eclipse.persistence.internal.queries.ExpressionQueryMechanism.prepareSelectAllRows(ExpressionQueryMechanism.java:1723)
        at org.eclipse.persistence.queries.ReadAllQuery.prepareSelectAllRows(ReadAllQuery.java:904)
        at org.eclipse.persistence.queries.ReadAllQuery.prepare(ReadAllQuery.java:835)
        at org.eclipse.persistence.queries.DatabaseQuery.checkPrepare(DatabaseQuery.java:673)
        ... 151 more
Caused by: java.lang.ClassCastException: java.lang.String cannot be cast to de.drvbund.pub.enums.DokumentTypSchluessel

我想这个框架需要 toString() -代表 Enum 元素，假定它是需要转换为其相应dbvalue的实体属性值，并尝试调用 convertToDatabaseColumn() 方法通过 String . 我只是不知道该怎么做才对。
如何检索由 Enum jpa属性值？