Indexes on Maps

[Kai]

Hi,

I wanted to get a better understanding of how indexes work on HashMaps with Morphia.

If I have an object like this:

class Job {

  @Indexed

  Map<String, String> taskMap = new HashMap<String, String>();

}

Will each key that gets stored in "taskMap" be indexed for fast retrieval?

Thanks.

[Scott Hernandez]

Not in the way you think. A map turns into this structure:

taskMap: {
key1 : value,
key2 : value,
...
}

And the index will be created on taskMap, not taskMap.* (which isn't
supported on the server), and indexes the complete embedded doc.

I think you want this structure:

taskMap : [
{name: key1, value: value },
{name: key1, value: value },
...
]

And then you can index the "name" field so you can quickly find the
docs with a certain name (key in the map example).

Also, your terminology "for fast retrieval" is confusing. What do you
mean by that? Is there some query you want to perform well?

[Kai]

Sorry, am a bit confused. To give a better example,

If I have Traveller Class that wraps hashmap with potential values like this:

site: Grand Canyon

travelMedium: Car

yearVisited: 2010

Class Traveller {

@Indexed

  Map<String, String> taskMap = new HashMap<String, String>();

}

I wanted to have each potential "key" in the Map be indexed, so when I write a query to get all Travellers who have visited Grand Canyon between 2006-2010, the query speed would be fast since each key is indexed.

Can you please describe how the object structure you mentioned above would look like in Java using Morphia?

Thanks!

[Kai]

Thanks for the tip Scott. I converted my map to a list of objects which essentially contains a key/value field and both fields are index. This way, I can achieve something like a map.* index.

Thanks again!