methods to check elements without deserialization

cache.h

@@ -42,6 +42,7 @@ public:
     virtual bool forceRecord(const K& key, const V& value) override;
     virtual void changeRecord(const K& key, const V& value) override;
     virtual void removeRecord(const K& key) override;
+    virtual bool checkRecord(const K& key) const override;
     virtual V getRecord(const K& key) const override;
     virtual uint32_t count() const override;
     virtual int drop(MDB_txn * transaction) override;

cache.hpp

@@ -137,11 +137,41 @@ V DataBase::Cache<K, V>::getRecord(const K& key) const {
         handleMode();
         return value;
     } catch (const NotFound& error) {
-        abscent->insert(key);
+        if (*mode != Mode::full) {
+            abscent->insert(key);
+        }
         throw error;
     }
 }
 
+template<class K, class V>
+bool DataBase::Cache<K, V>::checkRecord(const K& key) const {
+    if (!DataBase::Table<K, V>::db->opened) {
+        throw Closed("checkRecord", DataBase::Table<K, V>::db->name, DataBase::Table<K, V>::name);
+    }
+
+    typename std::map<K, V>::const_iterator itr = cache->find(key);
+    if (itr != cache->end()) {
+        return true;
+    }
+
+    if (*mode == Mode::full || abscent->count(key) != 0) {
+        return false;
+    }
+
+    try {
+        V value = Table<K, V>::getRecord(key);
+        cache->insert(std::make_pair(key, value));
+        handleMode();
+        return true;
+    } catch (const NotFound& error) {
+        if (*mode != Mode::full) {
+            abscent->insert(key);
+        }
+        return false;
+    }
+}
+
 template<class K, class V>
 std::map<K, V> DataBase::Cache<K, V>::readAll() const {
     if (!DataBase::Table<K, V>::db->opened) {

table.h

@@ -58,6 +58,7 @@ public:
     virtual bool forceRecord(const K& key, const V& value);     //returns true if there was addition, false if change
     virtual void changeRecord(const K& key, const V& value);
     virtual void removeRecord(const K& key);
+    virtual bool checkRecord(const K& key) const;               //checks if there is a record with given key
     virtual V getRecord(const K& key) const;
     virtual std::map<K, V> readAll() const;
 

table.hpp

@@ -141,6 +141,32 @@ V DataBase::Table<K, V>::getRecord(const K& key) const {
     }
 }
 
+template<class K, class V>
+bool DataBase::Table<K, V>::checkRecord(const K& key) const {
+    if (!db->opened) {
+        throw Closed("checkRecord", db->name, name);
+    }
+
+    MDB_val lmdbKey = keySerializer->setData(key);
+    MDB_val lmdbData;
+
+    MDB_txn *txn;
+    int rc;
+    mdb_txn_begin(db->environment, NULL, MDB_RDONLY, &txn);
+    rc = mdb_get(txn, dbi, &lmdbKey, &lmdbData);
+    mdb_txn_abort(txn);
+
+    if (rc) {
+        if (rc == MDB_NOTFOUND) {
+            return false;
+        } else {
+            throw Unknown(db->name, mdb_strerror(rc), name);
+        }
+    } else {
+        return true;
+    }
+}
+
 template<class K, class V>
 std::map<K, V> DataBase::Table<K, V>::readAll() const {
     if (!db->opened) {