Using field instead of "_id" for more-like-this query - elasticsearch

Question

I have a slug field that I want to use to identify object to use as a reference instead of "_id" field. But instead of using it as a reference, doc seems to use it as query to comapre against. Since slug is a unique field with a simple analyzer, it just returns exactly one result like the following. As far as I know, there is no way to use a custom field as _id field:
https://github.com/elastic/elasticsearch/issues/6730
So is double look up, finding out elasticsearch's id first then doing more_like_this the only way to achieve what I am looking for? Someone seems to have asked a similar question three years ago, but it doesn't have an answer.
ArticleDocument.search().query("bool",
should=Q("more_like_this",
fields= ["slug", "text"],
like={"doc": {"slug": "OEXxySDEPWaUfgTT54QvBg",
}, "_index":"article", "_type":"doc"},
min_doc_freq=1,
min_term_freq=1
)
).to_queryset()
Returns:
<ArticleQuerySet [<Article: OEXxySDEPWaUfgTT54QvBg)>]>

Answer 1

You can make some of your documents field as "default" _id while ingesting data.
Logstash
output {
elasticsearch {
hosts => ["localhost:9200"]
index => "my_name"
document_id => "%{some_field_id}"
}
}
Spark (Scala)
DF.saveToEs("index_name" + "/some_type", Map("es.mapping.id" -> "some_field_id"))
Index API
PUT twitter/_doc/1
{
"user" : "kimchy",
"post_date" : "2009-11-15T14:12:12",
"message" : "trying out Elasticsearch"
}
{
"_shards" : {
"total" : 2,
"failed" : 0,
"successful" : 2
},
"_index" : "twitter",
"_type" : "_doc",
"_id" : "1",
"_version" : 1,
"_seq_no" : 0,
"_primary_term" : 1,
"result" : "created"
}