Find the keywords that matched the query in Elastic Search - elasticsearch

Question

I'm using Elastic Search to search several indices.
When the user performs a query, the matches are split between 1 or 2 keywords that yield results. I'd like to be able to know for every hit, which keyword it originated from.
So if the user searched for "ventolin for asthma", I'd like to know which hits are for "ventolin" and which are for "asthma".
That is, for this query:
{
'query': {
'multi_match': {
'query': 'ventolin for asthma',
'fuzziness': 2,
'prefix_length': 1,
'type': 'best_fields',
'fields': ['term*']
}
}
}
And these hits:
{
...
'hits': {
'total': {
'value': 287,
'relation': 'eq'
},
'max_score': 10.301256,
'hits': [{
'_index': 'normalized-term-mapping',
'_type': '_doc',
'_id': '194526',
'_score': 10.301256,
'_source': {
'term': 'Ventolin Evohaler',
...
}
}, {
'_index': 'normalized-term-mapping',
'_type': '_doc',
'_id': '194362',
'_score': 8.529675,
'_source': {
'term': 'Childhood Asthma',
...
}
},
...
]
}
}
I want to match the first hit with the keyword Ventolin and the second hit with Asthma.
Note that:
I use fuzziness == 2, so the keywords may not exactly match the hit term
The indices use an analyzer (not a complex one but not trivial)
I can try and write code to match the terms with the query, but that would effectively mean reimplementing the elastic analysis in code which is not a great solution.
Is there a way to get the matched term from the original query from Elastic?

Answer 1

Yes, there is a way to get the matched terms using the Highlight API.
You're using a multi_match query so the default highlight options may be sufficient for you. You do need to specify the fields you want to highlight with something like this:
{
'query': {
'multi_match': {
'query': 'ventolin for asthma',
'fuzziness': 2,
'prefix_length': 1,
'type': 'best_fields',
'fields': ['term*']
}
},
'highlight': {
'fields': {
'term*': {}
}
}
}
However, this won't return an array of matched items. Instead, you will get the fields with existing matches marked (usually with HTML, but you can customize it). You could use that markup to post-process and isolate the individual matches if you need them.