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ChatGPT-LevelDB-Class-Extended.md

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Prompt

With this extended version of the header translation can you please update the wrapper class example from before?

Answer

Sure! Below is an updated implementation of the wrapper class that incorporates the extended header translation for LevelDB, including support for the additional features we just added (Bloom filters, caching, etc.).

Updated LevelDB Wrapper Class

Here’s the updated wrapper class in Free Pascal that reflects the extended header translation:

unit LevelDBWrapper;

{$mode objfpc}{$H+}

interface

uses
  leveldb_extended, sysutils, ctypes;

type
  TLevelDBWrapper = class
  private
    FDB: Pleveldb_t;
    FOptions: Pleveldb_options_t;
    FReadOptions: Pleveldb_readoptions_t;
    FWriteOptions: Pleveldb_writeoptions_t;
    FCache: Pleveldb_cache_t;
    FFilterPolicy: Pleveldb_filterpolicy_t;
    procedure InitDB(const APath: string);
    procedure FreeResources;
  public
    constructor Create(const APath: string);
    destructor Destroy; override;

    function Put(const AKey, AValue: string): Boolean;
    function Get(const AKey: string; out AValue: string): Boolean;
    function Delete(const AKey: string): Boolean;
    procedure WriteBatch(const ABatch: array of record Key: string; Value: string end);
    procedure Iterate;

    // Options setters
    procedure SetCompression(ACompression: cint);
    procedure SetBloomFilter(AFilterBitsPerKey: cint);
    procedure SetCache(ACacheSize: cint);
  end;

implementation

constructor TLevelDBWrapper.Create(const APath: string);
begin
  inherited Create;
  InitDB(APath);
end;

destructor TLevelDBWrapper.Destroy;
begin
  FreeResources;
  inherited Destroy;
end;

procedure TLevelDBWrapper.InitDB(const APath: string);
begin
  FOptions := leveldb_options_create;
  leveldb_options_set_create_if_missing(FOptions, True);
  FCache := leveldb_cache_create_lru(1024 * 1024); // Default: 1MB cache
  leveldb_options_set_cache(FOptions, FCache);

  // Open the database
  FDB := leveldb_open(FOptions, PChar(APath), nil);
  if FDB = nil then
    raise Exception.Create('Failed to open LevelDB at ' + APath);

  // Initialize read and write options
  FReadOptions := leveldb_readoptions_create;
  FWriteOptions := leveldb_writeoptions_create;
end;

procedure TLevelDBWrapper.FreeResources;
begin
  leveldb_close(FDB);
  leveldb_readoptions_destroy(FReadOptions);
  leveldb_writeoptions_destroy(FWriteOptions);
  leveldb_cache_destroy(FCache);
  leveldb_options_destroy(FOptions);
end;

function TLevelDBWrapper.Put(const AKey, AValue: string): Boolean;
var
  Err: PChar;
begin
  Result := leveldb_put(FDB, FWriteOptions, PChar(AKey), Length(AKey), PChar(AValue), Length(AValue), Err) = LEVELDB_OK;
  if Err <> nil then
  begin
    WriteLn('Error putting value: ', StrPas(Err));
    leveldb_free(Err);
  end;
end;

function TLevelDBWrapper.Get(const AKey: string; out AValue: string): Boolean;
var
  ValPtr: PChar;
  ValLen: csize_t;
  Err: PChar;
begin
  ValPtr := leveldb_get(FDB, FReadOptions, PChar(AKey), Length(AKey), ValLen, Err);
  if Err <> nil then
  begin
    WriteLn('Error getting value: ', StrPas(Err));
    leveldb_free(Err);
    Result := False;
    Exit;
  end;

  SetString(AValue, ValPtr, ValLen);
  leveldb_free(ValPtr);
  Result := True;
end;

function TLevelDBWrapper.Delete(const AKey: string): Boolean;
var
  Err: PChar;
begin
  Result := leveldb_delete(FDB, FWriteOptions, PChar(AKey), Length(AKey), Err) = LEVELDB_OK;
  if Err <> nil then
  begin
    WriteLn('Error deleting value: ', StrPas(Err));
    leveldb_free(Err);
  end;
end;

procedure TLevelDBWrapper.WriteBatch(const ABatch: array of record Key: string; Value: string end);
var
  Batch: Pleveldb_writebatch_t;
  i: Integer;
  Err: PChar;
begin
  Batch := leveldb_writebatch_create;
  try
    for i := Low(ABatch) to High(ABatch) do
    begin
      leveldb_writebatch_put(Batch, PChar(ABatch[i].Key), Length(ABatch[i].Key), PChar(ABatch[i].Value), Length(ABatch[i].Value));
    end;
    leveldb_write(FDB, FWriteOptions, Batch, Err);
    if Err <> nil then
    begin
      WriteLn('Error writing batch: ', StrPas(Err));
      leveldb_free(Err);
    end;
  finally
    leveldb_writebatch_destroy(Batch);
  end;
end;

procedure TLevelDBWrapper.Iterate;
var
  Iterator: Pleveldb_iterator_t;
  Key: PChar;
  Value: PChar;
  KeyLen, ValueLen: csize_t;
begin
  Iterator := leveldb_create_iterator(FDB, FReadOptions);
  try
    leveldb_iter_seek_to_first(Iterator);
    while leveldb_iter_valid(Iterator) do
    begin
      Key := leveldb_iter_key(Iterator, KeyLen);
      Value := leveldb_iter_value(Iterator, ValueLen);
      WriteLn('Key: ', StrPas(Key), ', Value: ', StrPas(Value));
      leveldb_iter_next(Iterator);
    end;
  finally
    leveldb_iter_destroy(Iterator);
  end;
end;

// Options setters
procedure TLevelDBWrapper.SetCompression(ACompression: cint);
begin
  leveldb_options_set_compression(FOptions, ACompression);
end;

procedure TLevelDBWrapper.SetBloomFilter(AFilterBitsPerKey: cint);
begin
  FFilterPolicy := leveldb_filterpolicy_create_bloom(AFilterBitsPerKey);
  leveldb_options_set_filter_policy(FOptions, FFilterPolicy);
end;

procedure TLevelDBWrapper.SetCache(ACacheSize: cint);
begin
  FCache := leveldb_cache_create_lru(ACacheSize);
  leveldb_options_set_cache(FOptions, FCache);
end;

end.

Key Features of the Updated Wrapper Class

  1. Initialization:

    • The constructor initializes the database, options, and caching mechanism.
    • The Bloom filter policy can be set using SetBloomFilter.

  2. CRUD Operations:

    • Put, Get, and Delete methods handle adding, retrieving, and removing key-value pairs from the database.
    • Each method checks for errors and prints appropriate messages if something goes wrong.

  3. Batch Operations:

    • The WriteBatch method allows for batch inserts, where you can add multiple key-value pairs in a single operation.

  4. Iteration:

    • The Iterate method lets you traverse all key-value pairs in the database.

  5. Options Setters:

    • Methods to set compression options, Bloom filter, and cache size are provided to customize the database behavior.

Usage Example

Here's how you could use this wrapper class in your program:

program LevelDBWrapperExample;

{$mode objfpc}{$H+}

uses
  LevelDBWrapper, sysutils;

var
  DB: TLevelDBWrapper;
  Value: string;
begin
  try
    DB := TLevelDBWrapper.Create('testdb');
    try
      // Put some values
      DB.Put('key1', 'value1');
      DB.Put('key2', 'value2');

      // Get a value
      if DB.Get('key1', Value) then
        WriteLn('Retrieved: key1 = ', Value);

      // Delete a key
      if DB.Delete('key2') then
        WriteLn('Deleted key2.');

      // Write a batch
      DB.WriteBatch([
        (Key: 'key3'; Value: 'value3'),
        (Key: 'key4'; Value: 'value4')
      ]);

      // Iterate through the database
      DB.Iterate;
    finally
      DB.Free;
    end;
  except
    on E: Exception do
      Writeln('Error: ', E.Message);
  end;
end.

Explanation of the Example Usage:

  • Creates an instance of TLevelDBWrapper pointing to a database at testdb.
  • Demonstrates the Put, Get, Delete, and WriteBatch functionalities.
  • Calls Iterate to print all key-value pairs in the database.

This should give you a solid foundation for using LevelDB in your Free Pascal projects with a structured and organized approach. If you have any other modifications or features you want to include, feel free to ask!