solr join function to query documents in multiple cores NullPointerException

Question

I use solr join to query documents from two cores, my cores is defined as follows: Post core:

        <fields>   
      <!-- general -->
    <field name="id"type="string"indexed="true"stored="true" multiValued="false" required="true"/>

    <field name="creatorId"type="string"indexed="true"stored="true"multiValued="false" required="true"/>
    .
    .
    .

</fields>

User core:

 <fields>   
  <!-- general -->
  <field name="id"        type="string"    indexed="true"  stored="true"  multiValued="false" required="true"/>
  <field name="username"      type="string"    indexed="true"  stored="true"  multiValued="false" /> 
  <field name="email"      type="string"    indexed="true"  stored="true"  multiValued="false" /> 
  <field name="userBrief"      type="string"    indexed="true"  stored="true"  multiValued="false" /> 
  <field name="jobNumber"      type="string"    indexed="true"  stored="true"  multiValued="false" />   
</fields>

now I want to query all user who has created post, I use join function, my url is like this:

http://localhost:9080/solr/user/select?q=*:*&fq={!join from=creatorId to=id fromIndex=post}

but it don't work, and it throw a exception:

null: java.lang.NullPointerException
      at org.apache.lucene.search.IndexSearcher.rewrite(IndexSearcher.java:559)
      at org.apache.lucene.search.IndexSearcher.createNormalizedWeight(IndexSearcher.java:646)
      at org.apache.lucene.search.IndexSearcher.search(IndexSearcher.java:280)
      .
      .
      .

I don't know why, can you help me?

Answer 1

The fq parameter requires a valid query with the !join.

Try adding an everything search to the end of the fq param like this. http://localhost:9080/solr/user/select?q=*:*&fq={!join from=creatorId to=id fromIndex=post}*:*

In a realistic setting you would likely want to filter the joined results in some way, for example, "Find me all action movies rated by this user updated in the past two weeks," where the movies and user ratings are stored as separate documents.