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Showing content from https://github.com/CoreyKaylor/Lightning.NET below:

CoreyKaylor/Lightning.NET: .NET library for LMDB key-value store

Lightning.NET is a .NET library that provides a fast and easy-to-use interface to the Lightning Memory-Mapped Database (LMDB), a high-performance key-value store. This library enables .NET developers to leverage LMDB's efficiency and reliability in their applications.

• High Performance: Direct interaction with LMDB ensures minimal overhead (no copies / 0-alloc when using Span) and maximum speed.
• Simplicity: The API is designed to be straightforward, making it easy to integrate into existing projects.
• Flexibility: Supports various database configurations, including handling multiple values for the same key.
• Reliable: It is fully transactional with complete ACID semantics.

Lightning.NET is available as a NuGet package. To install it, run the following command in the Package Manager Console:

Install-Package LightningDB

Alternatively, you can install it via the .NET CLI:

dotnet add package LightningDB

Here's a simple example demonstrating how to create an environment, open a database, and perform basic put and get operations:

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, UTF8.GetBytes("hello"), 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($"{UTF8.GetString(key)}: {UTF8.GetString(value)}");
            }
            else
            {
                Console.WriteLine("Key not found.");
            }
        }
    }
}

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".

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.

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

The Official LMDB API documentation is also a valuable resource for understanding the underlying database engine.

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