GAE w / Objectify - Can you request a HashMap?
In GAE, when using Objectify, can you query the HashMap? If so, how would you write it?
ofy().load().type(MyClass.class).filter("hashMapfieldName", "keyQueryinggFor").list();
Doesn't seem to work where hashMapfieldName
is HashMap<String, String>
. I am looking to find objects where hashMapfieldName
a specific key contains.
source to share
Just like the built-in classes, Objectify converts Map<String, String>
to a low-level object EmbeddedEntity
that is not indexed. However, if you @Index on a field Map
(or a nested class field), Objectify will create a synthetic index that will allow you to execute the query anyway.
Following your example, let's say you have a Named Map field hashMapfieldName
containing a mapping of rows "key"
to "value"
. This query syntax returns objects that have a pair:
ofy().load().type(MyClass.class).filter("hashMapfieldName.key", "value");
If you're just looking for the existence of a key, give it a try filter("hashMapfieldName.key !=", null)
.
source to share
I have a similar case where I have stored device specific values in an embedded hashmap where the device id is the key and I need to query for all objects that contain a specific value.
The suggested solution above actually works in my test environment. But I realized that I could not use this real application as it would not scale for the number of users we are designing. This is because Objectify will generate a property index for each hashmap key that I save . In my case, this means that each user device will have its own index, which could be 100,000 indexes!
So I went for this alternative approach instead:
- in the method
@OnSave
for the object, I store the values that I want to find in a separate indexed list that I only use for queries - then I will make my filtered request like this:
ofy().load().type(MyEntity.class).filter("values", value)
source to share
I'm not sure what Objectify
for HashMap
.
But according to the docs the HashMap
field type is not supported in Datastore
. Even if we serialize
save it, it will be saved as Blob, which is the default unindexded
.
As far as I know, HashMap
cannot be queried because no indexes have been created for it.
source to share