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From Semyon Boikov <sboi...@gridgain.com>
Subject Json support in Ignite
Date Wed, 15 Jul 2015 07:00:28 GMT
Hi all,

As part of integration with Node.Js (IGNITE-961) we age going to add in
Ignite support for JSON (possibility for IgniteCache to put, get, index and
query JSON data).

We can implement standard 'javax.json' API (JSR 353), with this API work
with cache will look like in this example:

*  javax.json.JsonProvider provider = ...; // Somehow get json API provider
from Ignite.*

*  IgniteCache<Long, javax.json.JsonObject> cache =

*  // Build json object using javax.json.JsonObjectBuilder.*
*  javax.json.JsonObject person = provider.createObjectBuilder().add("id",
1L).add("name", "John Doe").add("salary", 1000).build();*

*  cache.put(person.getJsonNumber("id").longValue(), person);*

*  // SQL clause which selects salaries based on range.*
*  String sql = "salary > ? and salary <= ?";*

*  // Execute queries for salary ranges.*
*  log.info <http://log.info>("People with salaries between 0 and 1000
(queried with SQL query): " +*
*    cache.query(new SqlQuery<Long, JsonObject>(JsonObject.class,
sql).setArgs(0, 1000)).getAll());*

Ignite should somehow provide access to 'javax.json' API, unfortunately
'javax.json' is not part of JDK so we have several options how it can be
added in Ignite:

1. Add dependency for 'javax.json-api' in core module, in this case we can
have method to get access for json API on 'org.apache.ignite.Ignite':

* interface Ignite {*
*    ...*

*    javax.json.JsonProvider json();*
* }*

* JsonProvider json = ignite.json();*

Not sure it is ok, since now we don't have 3rd party dependencies in ignite
'core' module except 'javax.cache' API.

2. Added another optional module 'json', this module will have dependency
for 'javax.json' API, and in this module we can have factory providing
access to 'javax.json' API:

* class IgniteJsonProvider {*
*    ...*

*    static IgniteJsonProvider json(Ignite ignite);*
* }*

* javax.json.JsonProvider provider = IgniteJsonProvider.json(ignite);*

3. Create plugin for json, in this case plugin will provide access to
'javax.json' API:

* IgniteJsonPlugin jsonPlugin = ignite.plugin(IgniteJsonPlugin.NAME);*

* javax.json.JsonProvider provider = jsonPlugin.json();*

Not sure this aproach with plugin is ok, since now we don't have 'core'
ignite functionality implemented as plugins.

Also we need following functionality for json objects

1. Possibility to map json cache key to affinity key. This can be achieved
with custom affinity mapper:

    cache.setAffinityMapper(new AffinityKeyMapper() {
        @Override public Object affinityKey(Object key) {
            return ((JsonObject)key).getJsonNumber("orgId").longValue();

2. Efficient implementation for equals/hashCode for json cache keys.

One option is just have equals/hashCode like in HashMap.

Another option can be add special JsonConfiguration, it should be set in
CacheConfiguration and can contain following settings:
- list of fields to use in 'equals' and 'hashCode' calculation
- alternatively for equals/hashCode we can provide possibility to implement
custom comparator/hash code calculator
- JsonConfiguration can have setting for affinity key

So JsonConfiguration can look like this:

*class JsonConfiguration {*
*    /***
*     * Field names for hash code calculation.*
*     */*
*    public Collection<String> getKeyHashCodeFields();*

*    /***
*     * Field names to use .*
*     */*
*    public Collection<String> getKeyEqualsFields();*

*    /***
*     * Field name to get key which will be used for node affinity
*     */*
*    public String getAffinityKeyField();*

I need your feedback on these questions:
- is it ok to implement 'javax.json' API to support json for Ignite caches?
- if we implement 'javax.json' what is best way to add it in Ignite (see my
suggestion above: just add dependency for 'javax.json' API in 'core'
module, add special module or plugin)
- do we need to adde JsonConfiguration I described above?


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