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 ，<$ c $的 java.util.Map c> 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 object 似乎是一个保留字。例如 obj 是可以的。什么是当前在HQL中使用反引号转义的方式来在HQL中转义别名？

使用反向提供以下错误：

 线程main中的异常org.hibernate.QueryException：意外的char：
'`'[SELECT u.id AS id ，u.name AS text，u AS`object` FROM User u] 
  

解决方案<您可以通过使用自定义的别名映射转换器的解决方法来实现它，所以您的代码会变成类似于这样的内容。

  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 {
 $ b $ private Map< String，String> renameAliasMap; 
 
 
 public AliasToMapTransformer（Map< String，String> renameAliasMap）{
 this.renameAliasMap =（renameAliasMap == null）？ < String，String> emptyMap（）：renameAliasMap; 
 
 
 $ b @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]）; 
} 
} 
返回结果; 
 
 
 $ b public static Builder renameAlias（String alias，String newAlias）{
 return new Builder（）。renameAlias（alias，newAlias）; 
} 
 
 
 public static class Builder {
 $ b $ private Map< String，String> aliasConversionMap = new HashMap< String，String>（）; 
 
 
 public Builder renameAlias（String alias，String newAlias）{
 aliasConversionMap.put（alias，newAlias）; 
返回此; 
} 
 
 
 public AliasToMapTransformer build（）{
返回新的AliasToMapTransformer（aliasConversionMap）; 
} 
} 
} 
  

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);

... 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?

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]

解决方案

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()
    );

And then using this class:

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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