[elasticsearch-plugin] Allow script_fields in search request body

[Draykee]

Is your feature request related to a problem? Please describe.
There is currently no possibility to set script_fields to allow script evaluation for each hit.
https://www.elastic.co/guide/en/elasticsearch/reference/7.8/search-fields.html#script-fields

Describe the solution you'd like

• Add a search config entry to return a script_fields configuration.
• The field that contains the evaluated script value needs to be mapped to the search result
• "_source": true, needs to be set in the request body to still include the whole index document (When using script fields, the default response will not contain the _source field but only the custom field we have defined)

Additional context
Assuming the product should receive a location via custom fields. I would like to add geo location based search and therefore I extend the SearchInput with latitude , longitude (and als distance). Here is a example of a possible configutation:

indexMappingProperties: {
     location: {
         type: 'geo_point', // contains function arcDistance
     },
},
customProductMappings: {
     location: {
         graphQlType: 'String',
         valueFn: (product: Product) => {
             const custom = product.customFields.location;
             return `${custom.latitude},${location.longitude}`;
         },
     }
},
mapQuery: (query: any, input: SearchInput, searchConfig: DeepRequired<SearchConfig>) => {
  // Dummy implementation of the geo distance search
  const distance = input.radius;
  const lat = input.latitude;
  const lon = input.longitude;
  
  if (lat && lon && distance) {
      query.bool.must = {
          match_all: {},
      };
      query.bool.filter = {
          geo_distance: {
              distance: `${distance}km`,
              location: {
                  lat,
                  lon,
              },
          },
      };
  
  }
  
  return query;
},
// The new config entry !
scriptFields: (input) => {
     // assuming SearchInput was extended with latitude and longitude
    // this script would add a 
     const lat = input.latitude;
     const lon = input.longitude;
     return {
         distance: {
             script: `doc['location'].arcDistance(${lat}, ${lon})`,
         }
     }
}

This script will add a field with the distance like this inside the ElasticSearch response:

"fields": {
  "distance": [
    103861.9371616157
  ]
}

[Draykee]

I've been working on this and I'm nearly finished. I found out that createSyntheticProductIndexItem will not apply customProductMappings. This causes a script I want to apply to fail in a e2e test, because there is no value. Sure, I could no extend the script to check the field first, but I thought maybe it's also better to apply custom mappings to a synthetic product.

@michaelbromley What do you think?

customProductMappings: {
    answer: {
        graphQlType: 'Int!',
        valueFn: args => {
            return 42;
        },
    },
},
searchConfig: {
    scriptFields: {
        answerDouble: {
            graphQlType: 'Int!',
            environment: 'product',
            scriptFn: (input) => ({
                script: `doc['answer'].value * 2` // answer is not mapped for synthetic products
            })
        }
    }
}

[Izayda]

@Draykee hi! How did you managed to extend SearchInput from config? As i understand, it is impossible now

[Draykee]

@Izayda My example was just assuming that it was done. You can do it with another plugin or inside the vendure-config. Right now it's not possible - you are right.