Lightning.NET Documentation

LMDB supports duplicate keys if the database is configured with the DatabaseOpenFlags.DuplicatesSort flag.

To retrieve these values, you can use a Cursor:

1. Create a cursor with tx.CreateCursor(db).
2. Position it at the first occurrence using cursor.Set(key).
3. Iterate through duplicates using cursor.NextDuplicate() until it returns a resultCode other than MDBResultCode.Success.

Alternatively, you can use the convenience method cursor.AllValues(key) to get an IEnumerable of all values associated with that key.

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

// ... inside a transaction ...
using (var db = tx.OpenDatabase(configuration: dbConfig))
{
    var key = Encoding.UTF8.GetBytes("fruit");
    tx.Put(db, key, Encoding.UTF8.GetBytes("apple"));
    tx.Put(db, key, Encoding.UTF8.GetBytes("cherry"));
    tx.Commit();
}

// ... retrieval using cursor ...
using (var cursor = tx.CreateCursor(db))
{
    var result = cursor.Set(key);
    if(result == MDBResultCode.Success)
    {
        do
        {
            var current = cursor.GetCurrent();
            Console.WriteLine($"{Encoding.UTF8.GetString(current.key.AsSpan())}: {Encoding.UTF8.GetString(current.value.AsSpan())}");
        }
        while (cursor.NextDuplicate().resultCode == MDBResultCode.Success);
    }

    // Or simpler:
    var values = cursor.AllValues(key);
    foreach(var value in values)
    {
        Console.WriteLine($"fruit: {Encoding.UTF8.GetString(value.AsSpan())}");
    }
}

To use Lightning.NET, follow these steps:

1. Create a LightningEnvironment with a specified path and call .Open().
2. Start a transaction using env.BeginTransaction().
3. Open a database within that transaction using tx.OpenDatabase(). Use DatabaseOpenFlags.Create in the DatabaseConfiguration to create a new database.
4. Use tx.Put(db, key, value) to insert data and tx.Commit() to save changes.
5. To retrieve data, start a transaction (optionally with TransactionBeginFlags.ReadOnly) and use tx.Get(db, key). This returns a tuple containing resultCode, key, and value.

using System;
using System.Text;
using LightningDB;

class Program
{
    static void Main()
    {
        // Specify the path to the database environment
        using var env = new LightningEnvironment("path_to_your_database");
        env.Open();

        // Begin a transaction and open (or create) a database
        using (var tx = env.BeginTransaction())
        using (var db = tx.OpenDatabase(configuration: new DatabaseConfiguration { Flags = DatabaseOpenFlags.Create }))
        {
            // Put a key-value pair into the database
            tx.Put(db, Encoding.UTF8.GetBytes("hello"), Encoding.UTF8.GetBytes("world"));
            tx.Commit();
        }

        // Begin a read-only transaction to retrieve the value
        using (var tx = env.BeginTransaction(TransactionBeginFlags.ReadOnly))
        using (var db = tx.OpenDatabase())
        {
            var (resultCode, key, value) = tx.Get(db, Encoding.UTF8.GetBytes("hello"));
            if (resultCode == MDBResultCode.Success)
            {
                Console.WriteLine($"{Encoding.UTF8.GetString(key)}: {Encoding.UTF8.GetString(value)}");
            }
            else
            {
                Console.WriteLine("Key not found.");
            }
        }
    }
}

You can control how keys and duplicate values are sorted using DatabaseConfiguration. This is useful for non-lexicographical sorting (e.g., integers or UTF-8 strings).

• Use config.CompareWith(comparer) to define how keys are sorted.
• Use config.FindDuplicatesWith(comparer) to define how duplicate values for the same key are sorted.

Available comparers in LightningDB.Comparers:

Note: Reverse variants (e.g., ReverseSignedIntegerComparer) are available for most comparers.

var config = new DatabaseConfiguration
{
    Flags = DatabaseOpenFlags.Create | DatabaseOpenFlags.DuplicatesSort
};

// Sort keys as signed integers (negative values sort before positive)
config.CompareWith(SignedIntegerComparer.Instance);

// Sort duplicate values in reverse order
config.FindDuplicatesWith(ReverseBitwiseComparer.Instance);

using var db = tx.OpenDatabase(configuration: config);