a Map mapping question.

ffaerton · **Joined:** Wed Jul 05, 2006 10:37 pm **Posts:** 6

How would you go about mapping this Map variable:

Code:

Map<String, <List<String>> map

here's roughly what i have in my mapping file atm:

Code:

<map name="requestHeaders" access="field">
          <key column="requestHeaders"/>
          <map-key column="keys" type="string"/>
          <element column="values" type="java.util.List"/>
</map>

Which of course doesn't want to work. Any suguestions?

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

You have to use an intermediate entity, you cannot do it directly. That is, your POJO will contain a Map<String, CustomListOfString>, where CustomListOfStrings has its own DB identifier and a list of strings.

This isn't an hibernate restriction, it's a relational DB restriction. That shape cannot be described in SQL without the extra ID column that CustomListOfStrings provides.

ffaerton · **Joined:** Wed Jul 05, 2006 10:37 pm **Posts:** 6

yeah i was starting to think along those lines. I stoped cursing hibernate after i learnt that JDO didn't really do that kind of thing either.

I understand the relational restriction, though it would be nice as this is a common structure for hibernate to create a psuedo table to make this work. Though then it would create one hellova mapping problem if you imagine: Map<String, <List <List String>>> m.

dslevine · **Joined:** Thu May 26, 2005 12:20 am **Posts:** 72

I am doing something similar to this, and the underlying DB implementation is just a single String. I do a custom mapping in the Java VO load which basically splits the string on get and joins the collection on set. Then it's just a String-String mapping at the DB level. I can see why this wont work in more complex cases, but maybe for what you are doing it will...

dan

ffaerton · **Joined:** Wed Jul 05, 2006 10:37 pm **Posts:** 6

aaaah nice one :)

but alas i loath filling my code with getters and setters lol.

dslevine · **Joined:** Thu May 26, 2005 12:20 am **Posts:** 72

Here's some code to get you started along that treachorous path... =)

Code:

   public void setMetricsMap(Map<String, String[]> deepMap) {
      Map<String,String> map = new HashMap<String,String>();
      Iterator<String> it = deepMap.keySet().iterator();
      String key;
      while(it.hasNext()) {
         key = it.next();
         map.put(key,StringUtils.join(deepMap.get(key), '|'));
      }
      this.setFlatMetricsMap(map);
   }

   public Map<String, String[]> getMetricsMap() {
      Map<String,String> flatMap = this.getFlatMetricsMap();
      Map<String,String[]> map = new HashMap<String, String[]>();
      Iterator<String> it = flatMap.keySet().iterator();
      String key;
      while(it.hasNext()) {
         key = it.next();
         map.put(key,StringUtils.split(flatMap.get(key), '|'));
      }
      return map;
   }

Then map the field flatMetricsMap in your Hibernate code and call the metricsMap field in your Java code.

Have fun!