ElasticSearch equivalent to MongoDB .distinct(...)
Let’s say we have an ElasticSearch index called strings with a field pattern
of {"type": "keyword"}
.
Now we want to do the equivalent of MongoDB db.getCollection('...').distinct('pattern')
:
Solution
In Python you can use the iterate_distinct_field()
helper from this previous post on ElasticSearch distinct. Full example:
from elasticsearch import Elasticsearch
es = Elasticsearch()
def iterate_distinct_field(es, fieldname, pagesize=250, **kwargs):
"""
Helper to get all distinct values from ElasticSearch
(ordered by number of occurrences)
"""
compositeQuery = {
"size": pagesize,
"sources": [{
fieldname: {
"terms": {
"field": fieldname
}
}
}
]
}
# Iterate over pages
while True:
result = es.search(**kwargs, body={
"aggs": {
"values": {
"composite": compositeQuery
}
}
})
# Yield each bucket
for aggregation in result["aggregations"]["values"]["buckets"]:
yield aggregation
# Set "after" field
if "after_key" in result["aggregations"]["values"]:
compositeQuery["after"] = \
result["aggregations"]["values"]["after_key"]
else: # Finished!
break
# Usage example
for result in iterate_distinct_field(es, fieldname="pattern.keyword", index="strings"):
print(result) # e.g. {'key': {'pattern': 'mypattern'}, 'doc_count': 315}