Ticket #473: postingiterator-from-query-wip.patch

xapian-core/api/database.cc

@@ -196 +196 @@
     return PostingIterator(new PostingIterator::Internal(pl, *this));
 }
 
+PostingIterator
+Database::postlist_begin(const Xapian::Query& query, bool prestart) const
+{
+    PostList* pl = internal->open_post_list(query, prestart);
+    if (!pl) return PostingIterator();
+    return PostingIterator(new PostingIterator::Internal(pl, *this));
+}
+
 TermIterator
 Database::termlist_begin(Xapian::docid did) const
 {

xapian-core/api/postingiteratorinternal.h

@@ -69 +69 @@
     }
 
     bool next() {
-        (void)pl->next();
+        auto prune = pl->next();
+        if (rare(prune)) {
+            delete pl;
+            pl = prune;
+        }
         return !pl->at_end();
     }
 
     bool skip_to(Xapian::docid did) {
-        (void)pl->skip_to(did);
+        auto prune = pl->skip_to(did);
+        if (rare(prune)) {
+            delete pl;
+            pl = prune;
+        }
         return !pl->at_end();
     }
 

xapian-core/backends/databaseinternal.cc

@@ -25 +25 @@
 
 #include "api/termlist.h"
 #include "heap.h"
+#include "matcher/localsubmatch.h"
+#include "matcher/postlisttree.h"
 #include "omassert.h"
 #include "postlist.h"
 #include "slowvaluelist.h"
@@ -77 +79 @@
     return get_doclength_upper_bound();
 }
 
+PostList*
+Database::Internal::open_post_list(const Query& query, bool prestart) const
+{
+    // FIXME: query_length wtscheme
+    Xapian::termcount query_length = query.get_length();
+    // FIXME: Move to Enquire?
+    // FIXME: Also need special implementations for multi and remote (or UnimplementedError)
+    BoolWeight wtscheme;
+    LocalSubMatch localsubmatch(this, query, query_length, wtscheme, 0);
+    Xapian::Database db(const_cast<Database::Internal*>(this));
+
+    // FIXME: Need to arrange for these to be deleted.
+    ValueStreamDocument* vsdoc = new ValueStreamDocument{db};
+    PostListTree* pltree = new PostListTree(*vsdoc, db, wtscheme);
+
+    Xapian::termcount total_subqs_i = 0;
+    auto plest = localsubmatch.get_postlist(pltree, &total_subqs_i);
+    PostList* pl = plest.pl;
+    if (!prestart) {
+        auto prune = pl->next();
+        if (rare(prune)) {
+            delete pl;
+            pl = prune;
+        }
+    }
+    return pl;
+}
+
 // Discard any exceptions - we're called from the destructors of derived
 // classes so we can't safely throw.
 void

xapian-core/backends/databaseinternal.h

@@ -218 +218 @@
     /** Return a PostList suitable for use in a PostingIterator. */
     virtual PostList* open_post_list(std::string_view term) const = 0;
 
+    /*virtual*/ PostList* open_post_list(const Query& query, bool prestart) const;
+
     /** Create a LeafPostList for use during a match.
      *
      *  @param term             The term to open a postlist for, or the empty

xapian-core/include/xapian/database.h

@@ -47 +47 @@
 
 class Compactor;
 class Document;
+class Query;
 class WritableDatabase;
 
 /** An indexed database of documents.
@@ -260 +261 @@
         return PostingIterator();
     }
 
+    PostingIterator postlist_begin(const std::string& term) const {
+        return postlist_begin(std::string_view{term});
+    }
+
+    /** End iterator corresponding to postlist_begin(). */
+    PostingIterator postlist_end(const std::string&) const noexcept {
+        return PostingIterator();
+    }
+
+    /** Start iterating the postings of a Query object.
+     *
+     *  This returns the document ids matching a query.  The key difference
+     *  compared to Enquire::get_mset() are that it can only return in
+     *  ascending document id order.  However get_mset() needs O(n) memory
+     *  so this can be useful if you want to process a lot of results.
+     *
+     *  @param query    The query to iterate the postings from.
+     *  @param prestart If true the returned iterator needs incrementing to
+     *                  be at the first result.  This is mainly useful as
+     *                  you can call get_description() and see the results
+     *                  of Xapian's query optimisation.  (Default: false)
+     *
+     *  @since Added in 1.5.0.
+     */
+    PostingIterator postlist_begin(const Xapian::Query& query,
+                                   bool prestart = false) const;
+
+    /** End iterator corresponding to postlist_begin(). */
+    PostingIterator postlist_end(const Xapian::Query&,
+                                 bool = false) const noexcept {
+        return PostingIterator();
+    }
+
     /** Start iterating the terms in a document.
      *
      *  @param did      The document id to iterate terms from