java - 如何转义 Hibernate 的 HQL 中的保留字

Question

我使用下面的查询来获取一个 java.util.Map，索引为 id、text 和 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);

... 但是 object 似乎是一个保留字。例如 obj 就可以了。当前在 HQL 中转义 别名 的方式是什么，就像 MySQL 使用反引号转义一样？

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]

Answer 1

您可以通过使用自定义“映射别名”转换器的解决方法来实现它，因此您的代码将更改为类似这样的内容

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()
    );

然后使用这个类:

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);
        }
    }
}