add unreport, check errors better

lmdb-safe.cc

@@ -147,6 +147,13 @@ MDBDbi MDBEnv::openDB(const char* dbname, int flags)
   return rwt.openDB(dbname, flags);
 }
 
+void MDBRWTransaction::clear(MDB_dbi dbi)
+{
+  if(int rc = mdb_drop(d_txn, dbi, 0)) {
+    throw runtime_error("Error clearing database: " + MDBError(rc));
+  }
+}
+
 MDBRWCursor MDBRWTransaction::getCursor(const MDBDbi& dbi)
 {
   return MDBRWCursor(this, dbi);

lmdb-safe.hh

@@ -271,6 +271,8 @@ public:
     d_parent->decRWTX();
   }
 
+  void clear(MDB_dbi dbi);
+  
   void put(MDB_dbi dbi, const MDB_val& key, const MDB_val& val, int flags=0)
   {
     if(!d_txn)
@@ -318,6 +320,11 @@ public:
   {
     d_cursors.insert(child);
   }
+  void unreportCursor(MDBRWCursor* child)
+  {
+    d_cursors.erase(child);
+  }
+  
   void reportCursorMove(MDBRWCursor* from, MDBRWCursor* to)
   {
     d_cursors.erase(from);
@@ -370,11 +377,15 @@ public:
   {
     if(d_cursor)
       mdb_cursor_close(d_cursor);
+    d_parent->unreportCursor(this);
   }
 
   int get(MDB_val& key, MDB_val& data, MDB_cursor_op op)
   {
-    return mdb_cursor_get(d_cursor, &key, &data, op);
+    int rc = mdb_cursor_get(d_cursor, &key, &data, op);
+    if(rc && rc != MDB_NOTFOUND)
+      throw std::runtime_error("mdb_cursor_get: " + string(mdb_strerror(rc)));
+    return rc;
   }
 
   int put(MDB_val& key, MDB_val& data, int flags=0)

multi-example.cc

@@ -0,0 +1,38 @@
+#include "lmdb-safe.hh"
+
+int main()
+{
+  auto env = getMDBEnv("multi",  0, 0600);
+  auto dbi = env->openDB("qnames", MDB_DUPSORT | MDB_CREATE);
+
+  auto txn = env->getRWTransaction();
+  txn.clear(dbi);
+
+  txn.put(dbi, "bdb", "old");
+  txn.put(dbi, "lmdb", "hot");
+  txn.put(dbi, "lmdb", "fast");
+  txn.put(dbi, "lmdb", "zooms");
+  txn.put(dbi, "mdb", "old name");
+
+  std::string_view v1;
+  if(!txn.get(dbi, "mdb", v1)) {
+    cout<<v1<<endl;
+  }
+  else {
+    cout << "found nothing" << endl;
+  }
+  txn.commit();
+  
+  txn = env->getRWTransaction();
+  auto cursor = txn.getCursor(dbi);
+  int count=0;
+  MDB_val key{4, (char*)"lmdb"};
+  MDB_val data{0,0};
+  int rc=0;
+  while(!(rc=cursor.get(key, data, count ? MDB_NEXT_DUP : MDB_SET))) {
+    std::string_view k((char*)key.mv_data, key.mv_size);
+    std::string_view v((char*)data.mv_data, data.mv_size);
+    cout << k << " = " << v <<endl;
+    ++count;
+  }
+}