如何在 Hibernate 的 HQL 中转义保留字 [英] How to escape reserved words in Hibernate's HQL

问题描述

我使用以下查询来获取带有索引 id、text 和 object 的 java.util.Map>:

I use the following query to get a java.util.Map with indexes id, text and 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 alias 的方法是什么，就像 MySQL 使用反引号转义一样?

... but object seems to be a reserved word. For example obj is OK. What is the current way to escape an alias in HQL the way MySQL uses backtick escapes?

使用反引号会出现以下错误:

Using backtick gives the following error:

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

推荐答案

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这样的内容

You could achieve it by a workaround using your custom "alias to map" transformer, so your code would change to something like this

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);
        }
    }
}

这篇关于如何在 Hibernate 的 HQL 中转义保留字的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！