Facets.md

Faceting

SolrNet supports faceted searching.

There are basically three kinds of facet queries:

1. querying by field
2. date facets
3. arbitrary facet queries

Facet queries are issued through the FacetQueries property of QueryOptions. Then the QueryOptions instance is passed to the server instance.

Facet Limits

There is a possibility that a field that you are using as a facet may have too many values and thus you may want to limit how many should be displayed. For this purpose we have the Limit property in SolrFacetFieldQuery.

Simply set Limit to the number of values that you want Solr to return for the specific facet and you are good to go.

 var fq = new SolrFacetFieldQuery("pepe") {Limit = 5};

Or on the other hand your project requires all facets to be returned and since Solr's default value for Limit is 100 then you may need to set to a higher number or even an unlimited value which is -1. Word of advise is that for performance considerations you set only to what you require and not unlimited.

Querying by field

Querying by field is handled by the SolrFacetFieldQuery class. Results are available through the FacetFields property.

Example: print all categories sorted by popularity.

ISolrOperations<Document> solr = ...
var r = solr.Query(SolrQuery.All, new QueryOptions {
    Rows = 0,
    Facet = new FacetParameters {
        Queries = new[] {new SolrFacetFieldQuery("category")}
    }
});
foreach (var facet in r.FacetFields["category"]) {
  Console.WriteLine("{0}: {1}", facet.Key, facet.Value);
}

Date facets

Date facet queries create facets from date ranges. Sample code:

ISolrOperations<Product> solr = ...
var results = solr.Query(SolrQuery.All, new QueryOptions {
    Facet = new FacetParameters {
        Queries = new[] {
            new SolrFacetDateQuery("timestamp", new DateTime(2001, 1, 1).AddDays(-1) /* range start */, new DateTime(2001, 1, 1).AddMonths(1) /* range end */, "+1DAY" /* gap */) {
                HardEnd = true,
                Other = new[] {FacetDateOther.After, FacetDateOther.Before}
            },
        }
    }
});
DateFacetingResult dateFacetResult = results.FacetDates["timestamp"];
foreach (KeyValuePair<DateTime, int> dr in dateFacetResult.DateResults) {
    Console.WriteLine(dr.Key);
    Console.WriteLine(dr.Value);
}

Arbitrary facet queries

Arbitrary facet queries are handled by the SolrFacetQuery class. Results are available through the FacetQueries property.

Example: segregate items by price (less than $500 - more than $500)

ISolrOperations<Document> solr = ...
var lessThan500 = new SolrQueryByRange<decimal>("price", 0m, 500m);
var moreThan500 = new SolrQueryByRange<string>("price", "500", "*");
var r = solr.Query(SolrQuery.All, new QueryOptions {
    Rows = 0,
    Facet = new FacetParameters {
        Queries = new[] {new SolrFacetQuery(lessThan500), new SolrFacetQuery(moreThan500)}
    }
});
foreach (var facet in r.FacetQueries) {
  Console.WriteLine("{0}: {1}", facet.Key, facet.Value);
}

Pivot faceting

Pivot faceting allows creating multidimensional facets. You can create a pivot facet with a main category and group by sub-categories.

In this example I will show you how to create a pivot facet that separates items by inStock but grouping them by in category.

Please look at the example below:

//Create a facet Pivot Query
var facetPivotQuery = new SolrFacetPivotQuery()
    {
        //Define 1 pivot, grouping cat by inStock
        //Multiple can be defined as well
        Fields = new[] { new PivotFields("inStock", "cat") },

        //Set the minCount to 1
        MinCount = 1
    };

//Create the facet parameters
//Note that you can use pivotQueries together with other facets queries
var facetParams = new FacetParameters()
{
    Queries = new[] { facetPivotQuery },

    //Limit the amounts of pivotRows to 15
    Limit = 15
};

var queryOptions = new QueryOptions();
queryOptions.Facet = facetParams;
queryOptions.Rows = 0;

var results = solr.Query("*:*", queryOptions);
if (results.FacetPivots.Count > 0)
{
    foreach (var pivotTable in results.FacetPivots)
    {
        System.Diagnostics.Debug.WriteLine("Pivot table for " + pivotTable.Key);
        foreach (var pivot in pivotTable.Value)
        {
            System.Diagnostics.Debug.WriteLine("  Pivot: " + pivot.Field + " with value " + pivot.Value + ". Child Pivots:");
            foreach (var pivotChild in pivot.ChildPivots)
            {
                System.Diagnostics.Debug.WriteLine("    - " + pivotChild.Value + " (" + pivotChild.Count + ")");
            }
        }
    }
}

This sample will create two main categories by inStock(true or false) and then broken down by cat (category). It will print out the following:

  Pivot: inStock with value true. Child Pivots:
    - electronics (10)
    - memory (3)
    - hard drive (2)
    - monitor (2)
    - search (2)
    - software (2)
    - camera (1)
    - copier (1)
    - multifunction printer (1)
    - music (1)
    - printer (1)
    - scanner (1)
  Pivot: inStock with value false. Child Pivots:
    - electronics (4)
    - connector (2)
    - graphics card (2)
    ```

Additional information to be found in:
http://wiki.apache.org/solr/HierarchicalFaceting#Pivot_Facets

http://wiki.apache.org/solr/SimpleFacetParameters#Pivot_.28ie_Decision_Tree.29_Faceting