Lucene.Net.Search.Query.ExtractTerms C# (CSharp) Method

        public virtual void ExtractTerms(ISet<Term> terms)
        {
            // needs to be implemented by query subclasses
            throw new System.NotSupportedException();
        }

        /// <summary> Create weight in multiple index scenario.
        ///
        /// Distributed query processing is done in the following steps:
        /// 1. rewrite query
        /// 2. extract necessary terms
        /// 3. collect dfs for these terms from the Searchables
        /// 4. create query weight using aggregate dfs.
        /// 5. distribute that weight to Searchables
        /// 6. merge results
        ///
        /// Steps 1-4 are done here, 5+6 in the search() methods
        ///
        /// </summary>
        /// <returns> rewritten queries
        /// </returns>
        public /*protected internal*/ override Weight CreateWeight(Query original, IState state)
        {
            // step 1
            Query rewrittenQuery = Rewrite(original, state);

            // step 2
            ISet <Term> terms = Lucene.Net.Support.Compatibility.SetFactory.CreateHashSet <Term>();

            rewrittenQuery.ExtractTerms(terms);

            // step3
            Term[] allTermsArray = terms.ToArray();
            int[]  aggregatedDfs = new int[terms.Count];
            for (int i = 0; i < searchables.Length; i++)
            {
                int[] dfs = searchables[i].DocFreqs(allTermsArray, state);
                for (int j = 0; j < aggregatedDfs.Length; j++)
                {
                    aggregatedDfs[j] += dfs[j];
                }
            }

            var dfMap = new Dictionary <Term, int>();

            for (int i = 0; i < allTermsArray.Length; i++)
            {
                dfMap[allTermsArray[i]] = aggregatedDfs[i];
            }

            // step4
            int            numDocs  = MaxDoc;
            CachedDfSource cacheSim = new CachedDfSource(dfMap, numDocs, Similarity);

            return(rewrittenQuery.Weight(cacheSim, state));
        }