In this example:

• We create a new LMDB environment at the specified path.
• We open a database within a transaction, inserting the key-value pair ("hello", "world").
• We commit the transaction to save the changes.
• We then start a read-only transaction to retrieve and display the value associated with the key "hello".

Handling Multiple Values for the Same Key

LMDB supports storing multiple values for a single key when the database is configured with the Dupsort flag. Here's how you can work with duplicate keys and use the cursor's NextDuplicate function:

using System;
using System.Text;
using LightningDB;

class Program
{
    static void Main()
    {
        using var env = new LightningEnvironment("path_to_your_database");
        env.Open();

        // Configure the database to support duplicate keys
        var dbConfig = new DatabaseConfiguration { Flags = DatabaseOpenFlags.Create | DatabaseOpenFlags.DuplicatesSort };

        // Begin a transaction and open the database
        using (var tx = env.BeginTransaction())
        using (var db = tx.OpenDatabase(configuration: dbConfig))
        {
            var key = Encoding.UTF8.GetBytes("fruit");
            var value1 = Encoding.UTF8.GetBytes("apple");
            var value2 = Encoding.UTF8.GetBytes("cherry");
            var value3 = Encoding.UTF8.GetBytes("banana");

            // Insert multiple values for the same key
            tx.Put(db, key, value1);
            tx.Put(db, key, value2);
            tx.Put(db, key, value3);
            tx.Commit();
        }

        // Begin a read-only transaction to retrieve the values
        using (var tx = env.BeginTransaction(TransactionBeginFlags.ReadOnly))
        using (var db = tx.OpenDatabase())
        using (var cursor = tx.CreateCursor(db))
        {
            var key = Encoding.UTF8.GetBytes("fruit");

            // Position the cursor at the first occurrence of the key
            var result = cursor.Set(key);
            if(result == MDBResultCode.Success)
            {
                do
                {
                    var current = cursor.GetCurrent();
                    var currentKey = current.key.AsSpan();
                    var currentValue = current.value.AsSpan();
                    Console.WriteLine($"{UTF8.GetString(currentKey)}: {UTF8.GetString(currentValue)}");
                }
                // Move to the next duplicate value
                while (cursor.NextDuplicate().resultCode == MDBResultCode.Success);
            }
            else
            {
                Console.WriteLine("Key not found.");
            }
            
            //Or even simpler
            var values = cursor.AllValuesFor(key);
            foreach(var value in values)
            {
                Console.WriteLine($"fruit: {Encoding.UTF8.GetString(value.AsSpan())}");
            }
        }
    }
}

In this example:

• We configure the database with the DupSort flag to allow multiple values for a single key.
• We insert three different values ("apple", "cherry", "banana") under the same key "fruit".
• Using a cursor, we iterate over all values associated with the key "fruit" by moving to the next duplicate entry and see the values retrieved are ordered.
• Then we demonstrate doing the same thing with IEnumerable instead.

Additional Resources

For more detailed examples and advanced usage, refer to the unit tests in the Lightning.NET repository.

The <a href="http://lmdb.tech/doc" target="_blank">Official LMDB API documentation</a> is also a valuable resource for understanding the underlying database engine.