(PECL solr >= 0.9.2)
SolrDocument::merge — Merges source to the current SolrDocument
Merges source to the current SolrDocument.
sourceDocThe source document.
overwrite
If this is true then fields with the same name in the destination document will be overwritten.
成功時(shí)返回 true， 或者在失敗時(shí)返回 false。