Introduction
When working with Elasticsearch, there are times when you may want to remove hits from the response to reduce the amount of data returned or to focus on specific information. This article will discuss various methods to remove hits from Elasticsearch response, including using the _source filtering, stored_fields parameter, and scripting.
1. Using _source Filtering
_source filtering allows you to include or exclude specific fields from the response. This can be useful when you want to remove certain fields from the hits in the response. To use _source filtering, you can add the _source parameter to your search query.
Example:
GET /index_name/_search
{
"_source": {
"includes": ["field1", "field2"],
"excludes": ["field3", "field4"]
},
"query": {
"match_all": {}
}
}In this example, the response will include only field1 and field2, while field3 and field4 will be excluded.
2. Using stored_fields Parameter
The stored_fields parameter allows you to specify which fields should be returned in the response. By default, all fields are returned in the _source, which is itself stored. To remove hits from the response, you can set the stored_fields parameter to an empty array.
Example:
GET /index_name/_search
{
"stored_fields": [],
"query": {
"match_all": {}
}
}In this example, no stored fields will be returned in the response, effectively removing the hits.
3. Using Script Fields
Script fields allow you to compute custom values for each hit in the response. You can use script fields to remove hits from the response by adding a condition in the script that filters out unwanted hits.
Example:
GET /index_name/_search
{
"script_fields": {
"custom_field": {
"script": {
"source": "if (doc['field1'].value > 10) { return doc['field1'].value; } else { return null; }"
}
}
},
"query": {
"match_all": {}
}
}In this example, the custom_field will only be added to the response if the value of field1 is greater than 10. If the condition is not met, the hit will be removed from the response.
4. Using Post-Filter
Post-filter is a feature that allows you to filter the search results after the initial query has been executed. This can be useful when you want to remove hits from the response based on specific criteria.
Example:
GET /index_name/_search
{
"query": {
"match_all": {}
},
"post_filter": {
"range": {
"field1": {
"gt": 10
}
}
}
}In this example, the post_filter will remove any hits where the value of field1 is less than or equal to 10.
5. Using Aggregations
Aggregations can be used to group and summarize data in the response. By using aggregations, you can effectively remove hits from the response and focus on the aggregated data.
Example:
GET /index_name/_search
{
"size": 0,
"aggs": {
"group_by_field1": {
"terms": {
"field": "field1"
}
}
}
}In this example, the size parameter is set to 0, which means no hits will be returned in the response. Instead, the response will contain the aggregated data grouped by the values of field1.
Conclusion
Removing hits from Elasticsearch response can be achieved using various methods, such as _source filtering, stored_fields parameter, scripting, post-filter, and aggregations. Depending on your use case and requirements, you can choose the most suitable method to filter out unwanted hits and focus on the relevant data.
Related log errors to this ES concept
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