the difference between the blockJoinParentQuery and blockJoinChildQuery in Solr

 The blockJoinParentQuery and blockJoinChildQuery parameters are used in Solr's Block Join feature to perform parent-child queries on a nested schema.

The blockJoinParentQuery parameter is used to specify the query that selects the parent documents in the block join query. This query should only match the parent documents in the index. It is used to filter the search results to include only those documents that have at least one matching child document.

The blockJoinChildQuery parameter, on the other hand, is used to specify the query that selects the child documents in the block join query. This query should only match the child documents in the index. It is used to filter the search results to include only those child documents that match the query criteria specified in the fq parameter.

In other words, the blockJoinParentQuery identifies the parent documents that should be included in the search results, and the blockJoinChildQuery identifies the child documents that should be included in the search results. Together, they allow you to perform a query that includes both parent and child documents in a nested schema.

It's worth noting that the blockJoinParentQuery and blockJoinChildQuery parameters are used in conjunction with the {!parent} and {!child} query parsers in Solr. The {!parent} parser is used to filter results to include only parent documents, and the {!child} parser is used to filter results to include only child documents.

import org.apache.solr.client.solrj.SolrClient; import org.apache.solr.client.solrj.SolrQuery; import org.apache.solr.client.solrj.impl.HttpSolrClient; public class BlockJoinExample { public static void main(String[] args) throws Exception { String solrUrl = "http://localhost:8983/solr/mycore"; SolrClient solrClient = new HttpSolrClient.Builder(solrUrl).build(); SolrQuery query = new SolrQuery(); // Set the parent query query.set("q", "*:*"); query.set("fq", "{!parent which='type:parent'}"); // Set the child query query.set("fq", "{!child of='type:parent'}name:child_name"); // Set the Block Join parameters query.set("blockJoinParentQuery", "{!parent which='type:parent'}"); query.set("blockJoinChildQuery", "{!child of='type:parent'}"); // Execute the query QueryResponse response = solrClient.query(query); SolrDocumentList results = response.getResults(); for (SolrDocument result : results) { System.out.println(result); } solrClient.close(); } }