At times, we may have a set of IDs that we would like to get them from Elasticsearch. The IDs query, as the name suggests, fetches the documents given a set of document IDs. It’s a much simpler way to fetch the documents in one go. The following listing shows how to retrieve some documents using a list of document IDs.

GET movies/_search
{
  "query": {
   "ids": { 
    "values": [10,4,6,8] 
   }
  }
 }

This query returns four documents with the corresponding four IDs. Each document that gets indexed has a mandatory _id field.

The metadata fields (like _id) can’t be part of the mapping schema. The _id field, along with other metadata fields like _source, _size, _routing etc. are part of the metadata fields pack and hence are not allowed to be part of the index mapping exercise.

We can also use a terms query to fetch documents if we have a set of document IDs instead of an IDs query. The following listing shows how we can do this.

GET movies/_search
{
  "query": {
   "terms": {
    "_id":[10,4,6,8]
   }
  }
 }

Here, we use a terms query, setting the array of document identifiers on the _id field as our search criteria.

These short articles are condensed excerpts taken from my book Elasticsearch in Action, Second Edition. The code is available in my GitHub repository.