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Indexes: Boosting

  • When querying with some filtering conditions, a basic score is calculated by the underlying engine for each document in the results.

  • Providing a boost value to selected fields allows prioritization of the resulting documents.
    The boos value is integrated with the basic score, increasing the document rank.

  • The automatic ordering of results by their score is configurable.

  • Boosting can be achieved in the following ways:

    • At query time:
      By applying a boost factor to searched terms at query time (see Boost search results).

    • Via index definition:
      By applying a boost factor in the index definition, as described in this article.

  • In this page:

Assign a boost factor to an index-field​

Applying a boost value to an index-field allows prioritization of matching documents based on an index-field.

The index:​
public class Orders_ByCountries_BoostByField : AbstractIndexCreationTask<Order>
{
  public class IndexEntry
  {
      // Index-field 'ShipToCountry' will be boosted in the map definition below
      public string ShipToCountry { get; set; }
      public string CompanyCountry { get; set; }
  }
  
  public Orders_ByCountries_BoostByField()
  {
      Map = orders => from order in orders
          let company = LoadDocument<Company>(order.Company)
          
          // Note: with current server version,
          // use 'select new' instead of 'select new IndexEntry' for compilation
          select new 
          {
              // Boost index-field 'ShipToCountry':
              // * Use method 'Boost', pass a numeric value to boost by 
              // * Documents that match the query criteria for this field will rank higher
              ShipToCountry = order.ShipTo.Country.Boost(10), 
              CompanyCountry = company.Address.Country
          };
  }
}
The query:​
List<Order> orders = session
   // Query the index    
  .Query<Orders_ByCountries_BoostByField.IndexEntry, Orders_ByCountries_BoostByField>()
  .Where(x => x.ShipToCountry == "Poland" || x.CompanyCountry == "Portugal")
  .OfType<Order>()
  .ToList();

// Because index-field 'ShipToCountry' was boosted (inside the index definition),
// then documents containing 'Poland' in their 'ShipTo.Country' field will get a higher score than
// documents containing a company that is located in 'Portugal'.

Assign a boost factor to the index-entry​

Applying a boost value to the whole index-entry allows prioritization of matching documents by content from the document.

The index:​
public class Orders_ByCountries_BoostByIndexEntry : AbstractIndexCreationTask<Order>
{
  public class IndexEntry
  {
      public string ShipToCountry { get; set; }
      public string CompanyCountry { get; set; }
  }
  
  public Orders_ByCountries_BoostByIndexEntry()
  {
      Map = orders => from order in orders
          let company = LoadDocument<Company>(order.Company)
          
          select new IndexEntry()
          {
              ShipToCountry = order.ShipTo.Country,
              CompanyCountry = company.Address.Country
          }
          // Boost the whole index-entry:
          // * Use method 'Boost'
          // * Pass a document-field that will set the boost level dynamically per document indexed.  
          // * The boost level will vary from one document to another based on the value of this field.
         .Boost((float) order.Freight);
  }
}
The query:​
List<Order> orders = session
   // Query the index  
  .Query<Orders_ByCountries_BoostByIndexEntry.IndexEntry, Orders_ByCountries_BoostByIndexEntry>()
  .Where(x => x.ShipToCountry == "Poland" || x.CompanyCountry == "Portugal")
  .OfType<Order>()
  .ToList();

// The resulting score per matching document is affected by the value of the document-field 'Freight'. 
// Documents with a higher 'Freight' value will rank higher.

Automatic score-based ordering​

  • By default, whenever boosting is applied, either via dynamic querying or when querying an index that has a boosting factor in its definition, the results will be automatically ordered by the score.

  • This behavior can be modified using the OrderByScoreAutomaticallyWhenBoostingIsInvolved
    configuration key.

  • Refer to the Get resulting score section to learn how to retrieve the calculated score of each result.