Retrieve keys in LMDB

Question

I wanted to access the key in lmdb from scala code as below:

 val file = new File("test.txt")
    val createEnv = create().setMapSize(10485760).setMaxDbs(1)
    val env = createEnv.open(file,MDB_NOSUBDIR)
    val db = env.openDbi(LMDBMain.DB_NAME, MDB_CREATE)
    //define key ,val pair 
    val key = allocateDirect(env.getMaxKeySize)
    val value = allocateDirect(700)
    //insert to db
    key.put("Greeting".getBytes(UTF_8)).flip
    value.put("Hello World".getBytes(UTF_8)).flip
    db.put(key, value)
    //fetching data 
    val txn = env.txnRead
    try {
      val fetchedKey : ByteBuffer = db.get(txn,key)
      val fetchedVal : ByteBuffer = txn.`val`()
      println(UTF_8.decode(fetchedVal).toString())
      println(UTF_8.decode(fetchedKey).toString())
      txn.commit()
    } finally if (txn != null) txn.close()

the output is :

HelloWorld

why I can't see greeting in my output !! any idea to how I can access key ?

Answer 1

Like in every map implementation, for accessing the keys, you need to iterate them:

try (CursorIterator<ByteBuffer> it = db.iterate(txn, KeyRange.all())) {
    for (final KeyVal<ByteBuffer> kv : it.iterable()) {
      println(UTF_8.decode(kv.key()).toString())
    }
}

You can see more examples in the code examples here