如何在Hibernate的HQL中转义保留字

  • Z时代
  • 2024-01-10
  • 分类：问答

我用下面的查询来获得java.util.Map与指数id，text以及object：

Query q = mySession.createQuery(
    "SELECT u.id AS id, u.name AS text, u AS object FROM User u")
    .setResultTransformer(Transformers.ALIAS_TO_ENTITY_MAP);

…但object似乎是保留字。例如obj可以。MySQL使用反引号转义的当前方式是如何在HQL中转义 别名 ？

使用反引号会出现以下错误：

Exception in thread "main" org.hibernate.QueryException: unexpected char: 
'`' [SELECT u.id AS id, u.name AS text, u AS `object` FROM User u]

回答：

您可以通过使用自定义“别名映射”转换器的解决方法来实现，因此您的代码将更改为如下所示

Query q = mySession.createQuery(
    "SELECT u.id AS id, u.name AS text, u AS obj FROM User u")
    .setResultTransformer(
        AliasToMapTransformer.renameAlias("obj", "object").build()
    );

然后使用此类：

public class AliasToMapTransformer extends BasicTransformerAdapter {
    private Map<String, String> renameAliasMap;
    public AliasToMapTransformer(Map<String, String> renameAliasMap) {
        this.renameAliasMap = (renameAliasMap == null) ? Collections.<String, String>emptyMap() : renameAliasMap;
    }
    @Override
    public Object transformTuple(Object[] tuple, String[] aliases) {
        Map<String, Object> result = new HashMap<String, Object>(tuple.length);
        for (int i = 0; i < tuple.length; i++) {
            String alias = aliases[i];
            if (alias != null) {
                String newAlias = renameAliasMap.get(alias);
                result.put((newAlias != null) ? newAlias : alias, tuple[i]);
            }
        }
        return result;
    }
    public static Builder renameAlias(String alias, String newAlias) {
        return new Builder().renameAlias(alias, newAlias);
    }
    public static class Builder {
        private Map<String, String> aliasConversionMap = new HashMap<String, String>();
        public Builder renameAlias(String alias, String newAlias) {
            aliasConversionMap.put(alias, newAlias);
            return this;
        }
        public AliasToMapTransformer build() {
            return new AliasToMapTransformer(aliasConversionMap);
        }
    }
}

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