unit orm_utils;

interface

uses
  System.SysUtils,
  System.Classes,
  System.Generics.Collections,
  System.Rtti,
  System.TypInfo,
  Data.DB,
  Uni,
  pixel_classes,
  orm_customattributes;

type
  EORMUtilsException = class(Exception);

  /// <summary>
  /// Base class for query record information
  /// Use descendants of this class to represent specific database records.
  /// </summary>
  TQryRecInfo = class
  private
    FDirtyFields: TDictionary<string, Boolean>;
    FPreviousValues: TDictionary<string, TValue>;
    procedure SetInfo(Index: Integer; const Value: TValue);
  public
    constructor Create;
    destructor Destroy; override;

    // Methods to set nullable fields
    procedure SetInfoNullableString(Index: Integer; const Value: TNullable<string>);
    procedure SetInfoNullableInteger(Index: Integer; const Value: TNullable<Integer>);
    procedure SetInfoNullableInt64(Index: Integer; const Value: TNullable<Int64>);
    procedure SetInfoNullableExtended(Index: Integer; const Value: TNullable<Extended>);
    procedure SetInfoNullableCurrency(Index: Integer; const Value: TNullable<Currency>);
    procedure SetInfoNullableDateTime(Index: Integer; const Value: TNullable<TDateTime>);
    procedure SetInfoNullableBoolean(Index: Integer; const Value: TNullable<Boolean>);
    procedure SetInfoNullableVariant(Index: Integer; const Value: TNullable<Variant>);

    // Methods to set non-nullable simple types
    procedure SetInfoCurrency(Index: Integer; const Value: Currency);
    procedure SetInfoString(Index: Integer; const Value: string);
    procedure SetInfoInteger(Index: Integer; const Value: Integer);
    procedure SetInfoInt64(Index: Integer; const Value: Int64);
    procedure SetInfoExtended(Index: Integer; const Value: Extended);
    procedure SetInfoDateTime(Index: Integer; const Value: TDateTime);
    procedure SetInfoBoolean(Index: Integer; const Value: Boolean);
    procedure SetInfoVariant(Index: Integer; const Value: Variant);

    // Methods to handle dirty fields
    function IsFieldDirty(const FieldName: string): Boolean;
    procedure ClearDirtyFlags;
    property DirtyFields: TDictionary<string, Boolean> read FDirtyFields;

    // Methods to handle previous values
    function GetPreviousValue(const FieldName: string): TValue;
    procedure ClearPreviousValues;
    property PreviousValues: TDictionary<string, TValue> read FPreviousValues;

    /// <summary>
    /// Retrieves the formatted text for a given field based on the FmtProp attribute.
    /// </summary>
    function GetFormattedText(const FieldName: string): string;

    /// <summary>
    /// Fetches data for this record from the database based on the provided SQL.
    /// </summary>
    procedure Fetch(DBConn: TUniConnection; const QryTxt: string);
  end;

  /// <summary>
  /// Generic class to handle arrays of TQryRecInfo descendants.
  /// </summary>
  TQryRecArray<T: class, constructor> = class
  private
    FQryRecInfoList: TObjectList<T>;
    FFilterSQL: string;
    FDBConn: TUniConnection;
    function GetCount: Integer;
  public
    constructor Create;
    destructor Destroy; override;

    /// <summary>
    /// Fetches all records based on the provided SQL text and populates the array.
    /// </summary>
    /// <param name="QryTxt">The base SQL query text.</param>
    procedure FetchAllInstance(DBConn: TUniConnection; const QryTxt: string);

    /// <summary>
    /// Clears any SQL filters applied.
    /// </summary>
    procedure ClearFilter;

    /// <summary>
    /// Accesses a record at the specified index.
    /// </summary>
    /// <param name="Index">The zero-based index of the record.</param>
    /// <returns>The record at the specified index.</returns>
    function Rec(Index: Integer): T;

    /// <summary>
    /// Number of records in the array.
    /// </summary>
    property RecCount: Integer read GetCount;

    /// <summary>
    /// Database connection used for fetching records.
    /// </summary>
    property DBConn: TUniConnection read FDBConn write FDBConn;

    /// <summary>
    /// Additional SQL filter to apply to the query.
    /// </summary>
    property SQLFilter: string read FFilterSQL write FFilterSQL;

    /// <summary>
    /// Provides support for for-in loops by returning an enumerator.
    /// </summary>
    function GetEnumerator: TEnumerator<T>;

    /// <summary>
    /// Factory method to create and fetch records in a single step.
    /// </summary>
    /// <param name="DBConn">Database connection.</param>
    /// <param name="QryTxt">SQL query text.</param>
    /// <returns>Populated instance of TQryRecArray<T>.</returns>
    class function FetchAll(DBConn: TUniConnection; const QryTxt: string): TQryRecArray<T>; static;
  end;

  // Example descendant of TQryRecInfo (You can create your own)
  TDynRec = class(TQryRecInfo)
    // Define additional properties as needed
  end;

implementation

uses
  System.Variants,
  StrUtils,
  pixel_utils; // Ensure this unit is in your project and properly implemented

{ TQryRecInfo }

constructor TQryRecInfo.Create;
begin
  inherited Create;
  FDirtyFields := TDictionary<string, Boolean>.Create;
  FPreviousValues := TDictionary<string, TValue>.Create;
end;

destructor TQryRecInfo.Destroy;
begin
  FDirtyFields.Free;
  FPreviousValues.Free;
  inherited;
end;

procedure TQryRecInfo.ClearDirtyFlags;
begin
  FDirtyFields.Clear;
end;

procedure TQryRecInfo.ClearPreviousValues;
begin
  FPreviousValues.Clear;
end;

function TQryRecInfo.IsFieldDirty(const FieldName: string): Boolean;
begin
  Result := FDirtyFields.ContainsKey(FieldName) and FDirtyFields[FieldName];
end;

function TQryRecInfo.GetPreviousValue(const FieldName: string): TValue;
begin
  if not FPreviousValues.TryGetValue(FieldName, Result) then
    raise EORMUtilsException.CreateFmt('No previous value found for field "%s".', [FieldName]);
end;

function FormataInfo(info: Variant; tipo: TFormatType): string;
begin
  if VarIsNull(info) or VarIsEmpty(info) then
    Exit('');

  case tipo of
    tiString:
      Result := VarToStr(info);
    tiInteger:
      Result := IntToStr(Integer(info));
    tiMoney:
      Result := FormatFloat(FMT_MONEY, Currency(info));
    tiFloat:
      Result := FloatToStr(info);
    tiDate:
      if VarIsType(info, [varDate, varDouble]) then
      begin
        if VarToDateTime(info) < EncodeDate(1900, 1, 1) then
          Result := ''
        else
          Result := FormatDateTime('dd/mm/yyyy', VarToDateTime(info));
      end
      else
        raise EORMUtilsException.CreateFmt('FormataInfo: Cannot treat information [%s] as tiDate.', [VarToStr(info)]);
    tiDateTime:
      if VarIsType(info, [varDate, varDouble]) then
      begin
        if VarToDateTime(info) = 0 then
          Result := ''
        else
          Result := FormatDateTime('dd/mm/yyyy hh:mm:ss', VarToDateTime(info));
      end
      else
        raise EORMUtilsException.CreateFmt('FormataInfo: Cannot treat information [%s] as tiDateTime.', [VarToStr(info)]);
    tiBoolean:
      Result := IfThen(Boolean(info), 'S', 'N');
    tiByteArray:
      Result := ByteArrayToHex(info);
    tiNone:
      Result := '';
  else
    raise EORMUtilsException.CreateFmt('FormataInfo: Format type [%s] not recognized.', [GetEnumName(TypeInfo(TFormatType), Integer(tipo))]);
  end;
end;

function TQryRecInfo.GetFormattedText(const FieldName: string): string;
var
  Ctx: TRttiContext;
  RttiType: TRttiType;
  Prop: TRttiProperty;
  Field: TRttiField;
  Value: TValue;
  FmtType: TFormatType;
  UnderlyingType: TRttiType;
  HasValueField: TRttiField;
  ValueField: TRttiField;
  HasValue: Boolean;
  ActualValue: TValue;
  Attr: TCustomAttribute;
  FmtAttr: FmtPropAttribute;
begin
  Result := '';
  Ctx := TRttiContext.Create;
  try
    RttiType := Ctx.GetType(Self.ClassType);

    // Find the property by name
    Prop := RttiType.GetProperty(FieldName);
    if not Assigned(Prop) then
      raise EORMUtilsException.CreateFmt('Property "%s" not found.', [FieldName]);

    // Get the value of the property
    Value := Prop.GetValue(Self);
    FmtType := tiNone;

    // Check for FmtProp attribute on the property
    for Attr in Prop.GetAttributes do
    begin
      if Attr is FmtPropAttribute then
      begin
        FmtAttr := FmtPropAttribute(Attr);
        FmtType := FmtAttr.FormatType;
        Break;
      end;
    end;

    // If not found on property, check on the corresponding field
    if FmtType = tiNone then
    begin
      Field := RttiType.GetField('_' + FieldName);
      if Assigned(Field) then
      begin
        for Attr in Field.GetAttributes do
        begin
          if Attr is FmtPropAttribute then
          begin
            FmtAttr := FmtPropAttribute(Attr);
            FmtType := FmtAttr.FormatType;
            Break;
          end;
        end;
      end;
    end;

    // Determine default FmtType based on property type if not set by attribute
    if FmtType = tiNone then
    begin
      UnderlyingType := Prop.PropertyType;

      // Handle TNullable<T>
      if UnderlyingType.TypeKind = tkRecord then
      begin
        ValueField := UnderlyingType.GetField('Value');
        if Assigned(ValueField) then
          UnderlyingType := ValueField.FieldType;
      end;

      case UnderlyingType.TypeKind of
        tkInteger, tkInt64:
          FmtType := tiInteger;
        tkFloat:
          if UnderlyingType.Handle = TypeInfo(TDateTime) then
            FmtType := tiDateTime
          else
            FmtType := tiFloat;
        tkString, tkLString, tkWString, tkUString:
          FmtType := tiString;
        tkEnumeration:
          if UnderlyingType.Handle = TypeInfo(Boolean) then
            FmtType := tiBoolean
          else
            FmtType := tiString;
        tkVariant:
          FmtType := tiString;
      else
        FmtType := tiNone;
      end;
    end;

    // Extract actual value from TNullable<T> if necessary
    if Value.Kind = tkRecord then
    begin
      // Assuming TNullable<T> has 'HasValue' and 'Value' fields
      UnderlyingType := Prop.PropertyType;
      HasValueField := UnderlyingType.GetField('HasValue');
      ValueField := UnderlyingType.GetField('Value');

      if Assigned(HasValueField) and Assigned(ValueField) then
      begin
        HasValue := HasValueField.GetValue(Value.GetReferenceToRawData).AsBoolean;
        if HasValue then
        begin
          ActualValue := ValueField.GetValue(Value.GetReferenceToRawData);
          // Format the actual value
          Result := FormataInfo(ActualValue.AsVariant, FmtType);
        end
        else
          Result := '';
      end
      else
      begin
        // Not TNullable<T>, handle value directly
        if not Value.IsEmpty then
          Result := FormataInfo(Value.AsVariant, FmtType)
        else
          Result := '';
      end;
    end
    else
    begin
      // Not a record, handle value directly
      if not Value.IsEmpty then
        Result := FormataInfo(Value.AsVariant, FmtType)
      else
        Result := '';
    end;
  finally
    // No need to free TRttiContext as it's a record
  end;
end;

procedure TQryRecInfo.Fetch(DBConn: TUniConnection; const QryTxt: string);
var
  qr: TUniQuery;
  Ctx: TRttiContext;
  ObjType: TRttiType;
  Prop: TRttiProperty;
  Field: TField;
  ORMFieldName: string;
begin
  if not Assigned(DBConn) or Trim(QryTxt).IsEmpty then
    Exit;

  qr := TUniQuery.Create(nil);
  try
    qr.Connection := DBConn;
    qr.SpecificOptions.Values['FetchAll'] := 'True';
    qr.SpecificOptions.Values['CreateConnection'] := 'False';
    qr.SQL.Text := QryTxt;
    qr.Open;

    if qr.RecordCount > 0 then
    begin
      Ctx := TRttiContext.Create;
      try
        ObjType := Ctx.GetType(Self.ClassType);

        for Prop in ObjType.GetProperties do
        begin
          if not Prop.IsWritable then
            Continue;

          // Attempt to find the corresponding field in the query
          Field := qr.FindField(Prop.Name);
          if not Assigned(Field) then
            Continue; // Field not found, skip

          ORMFieldName := '_' + Prop.Name;
          // Handle TNullable<T> types
          if Prop.PropertyType.TypeKind = tkRecord then
          begin
            // Expecting TNullable<T>
            // Attempt to find the backing field for the nullable property
            if ObjType.GetField(ORMFieldName) = nil then
              Continue; // Backing field not found, skip

            if Prop.PropertyType.Name.StartsWith('TNullable<') then
            begin
              // Use RTTI to determine the generic type parameter
              if Field.IsNull then
                ObjType.GetField(ORMFieldName).SetValue(Self, TValue.From<TNullable<string>>(NullValue))
              else
              begin
                if Prop.PropertyType.Name = 'TNullable<System.string>' then
                  ObjType.GetField(ORMFieldName).SetValue(Self, TValue.From<TNullable<string>>(Field.AsString))
                else if Prop.PropertyType.Name = 'TNullable<System.Integer>' then
                  ObjType.GetField(ORMFieldName).SetValue(Self, TValue.From<TNullable<Integer>>(Field.AsInteger))
                else if Prop.PropertyType.Name = 'TNullable<System.Int64>' then
                  ObjType.GetField(ORMFieldName).SetValue(Self, TValue.From<TNullable<Int64>>(Field.AsLargeInt))
                else if Prop.PropertyType.Name = 'TNullable<System.Extended>' then
                  ObjType.GetField(ORMFieldName).SetValue(Self, TValue.From<TNullable<Extended>>(Field.AsFloat))
                else if Prop.PropertyType.Name = 'TNullable<System.Currency>' then
                  ObjType.GetField(ORMFieldName).SetValue(Self, TValue.From<TNullable<Currency>>(Field.AsCurrency))
                else if Prop.PropertyType.Name = 'TNullable<System.TDateTime>' then
                  ObjType.GetField(ORMFieldName).SetValue(Self, TValue.From<TNullable<TDateTime>>(Field.AsDateTime))
                else if Prop.PropertyType.Name = 'TNullable<System.Boolean>' then
                  ObjType.GetField(ORMFieldName).SetValue(Self, TValue.From<TNullable<Boolean>>(Field.AsBoolean))
                else if Prop.PropertyType.Name = 'TNullable<System.Variant>' then
                  ObjType.GetField(ORMFieldName).SetValue(Self, TValue.From<TNullable<Variant>>(Field.Value))
                else
                  raise EORMUtilsException.CreateFmt('Unsupported TNullable type: %s', [Prop.PropertyType.Name]);
              end;
            end
            else
              raise EORMUtilsException.CreateFmt('Unsupported record type: %s', [Prop.PropertyType.Name]);
          end
          else
          begin
            // Handle non-nullable types
            case Prop.PropertyType.TypeKind of
              tkString, tkLString, tkWString, tkUString:
                ObjType.GetField(ORMFieldName).SetValue(Self, Field.AsString);
              tkInteger:
                ObjType.GetField(ORMFieldName).SetValue(Self, Field.AsInteger);
              tkInt64:
                ObjType.GetField(ORMFieldName).SetValue(Self, Field.AsLargeInt);
              tkFloat:
                if Prop.PropertyType.Handle = TypeInfo(Currency) then
                  ObjType.GetField(ORMFieldName).SetValue(Self, Field.AsCurrency)
                else
                  ObjType.GetField(ORMFieldName).SetValue(Self, Field.AsFloat);
              tkVariant:
                ObjType.GetField(ORMFieldName).SetValue(Self, TValue.FromVariant(Field.AsVariant));
              tkEnumeration:
                if Prop.PropertyType.Handle = TypeInfo(Boolean) then
                  ObjType.GetField(ORMFieldName).SetValue(Self, Field.AsBoolean)
                else
                  raise EORMUtilsException.CreateFmt('Unsupported enumeration type: %s', [Prop.PropertyType.Name]);
            else
              // Add additional handling for other types if necessary
            end;
          end;
        end;
      finally
        // No need to free TRttiContext as it's a record
      end;
    end;
  finally
    qr.Free;
  end;
end;

procedure TQryRecInfo.SetInfo(Index: Integer; const Value: TValue);
var
  PropName: string;
  PropKind: TTypeKind;
  Ctx: TRttiContext;
  Prop: TRttiProperty;
  Field: TRttiField;
  OldValue: TValue;
begin
  // Retrieve property name and kind based on index
  // Assuming that the index corresponds to the property order
  Ctx := TRttiContext.Create;
  try
    Prop := Ctx.GetType(Self.ClassType).GetProperties()[Index];
    if not Assigned(Prop) then
      raise EORMUtilsException.CreateFmt('Error: The index "%d" does not correspond to any property in class "%s".', [Index, ClassName]);

    PropName := Prop.Name;
    PropKind := Prop.PropertyType.TypeKind;

    Field := Ctx.GetType(Self.ClassType).GetField('_' + PropName);
    if not Assigned(Field) then
      raise EORMUtilsException.CreateFmt('Error: Field "_%s" not found in class "%s".', [PropName, ClassName]);

    // If the field is not yet dirty, store the previous value
    if not FDirtyFields.ContainsKey(PropName) then
    begin
      OldValue := Field.GetValue(Self);
      FPreviousValues.AddOrSetValue(PropName, OldValue);
    end;

    // Set the new value
    Field.SetValue(Self, Value);

    // Mark the property as dirty
    FDirtyFields.AddOrSetValue(PropName, True);
  finally
    // No need to free TRttiContext as it's a record
  end;
end;

procedure TQryRecInfo.SetInfoCurrency(Index: Integer; const Value: Currency);
begin
  SetInfo(Index, TValue.From<Currency>(Value));
end;

procedure TQryRecInfo.SetInfoString(Index: Integer; const Value: string);
begin
  SetInfo(Index, TValue.From<string>(Value));
end;

procedure TQryRecInfo.SetInfoInteger(Index: Integer; const Value: Integer);
begin
  SetInfo(Index, TValue.From<Integer>(Value));
end;

procedure TQryRecInfo.SetInfoInt64(Index: Integer; const Value: Int64);
begin
  SetInfo(Index, TValue.From<Int64>(Value));
end;

procedure TQryRecInfo.SetInfoExtended(Index: Integer; const Value: Extended);
begin
  SetInfo(Index, TValue.From<Extended>(Value));
end;

procedure TQryRecInfo.SetInfoDateTime(Index: Integer; const Value: TDateTime);
begin
  SetInfo(Index, TValue.From<TDateTime>(Value));
end;

procedure TQryRecInfo.SetInfoBoolean(Index: Integer; const Value: Boolean);
begin
  SetInfo(Index, TValue.From<Boolean>(Value));
end;

procedure TQryRecInfo.SetInfoVariant(Index: Integer; const Value: Variant);
begin
  SetInfo(Index, TValue.From<Variant>(Value));
end;

procedure TQryRecInfo.SetInfoNullableBoolean(Index: Integer; const Value: TNullable<Boolean>);
begin
  SetInfo(Index, TValue.From<TNullable<Boolean>>(Value));
end;

procedure TQryRecInfo.SetInfoNullableCurrency(Index: Integer; const Value: TNullable<Currency>);
begin
  SetInfo(Index, TValue.From<TNullable<Currency>>(Value));
end;

procedure TQryRecInfo.SetInfoNullableDateTime(Index: Integer; const Value: TNullable<TDateTime>);
begin
  SetInfo(Index, TValue.From<TNullable<TDateTime>>(Value));
end;

procedure TQryRecInfo.SetInfoNullableExtended(Index: Integer; const Value: TNullable<Extended>);
begin
  SetInfo(Index, TValue.From<TNullable<Extended>>(Value));
end;

procedure TQryRecInfo.SetInfoNullableInteger(Index: Integer; const Value: TNullable<Integer>);
begin
  SetInfo(Index, TValue.From<TNullable<Integer>>(Value));
end;

procedure TQryRecInfo.SetInfoNullableInt64(Index: Integer; const Value: TNullable<Int64>);
begin
  SetInfo(Index, TValue.From<TNullable<Int64>>(Value));
end;

procedure TQryRecInfo.SetInfoNullableString(Index: Integer; const Value: TNullable<string>);
begin
  SetInfo(Index, TValue.From<TNullable<string>>(Value));
end;

procedure TQryRecInfo.SetInfoNullableVariant(Index: Integer; const Value: TNullable<Variant>);
begin
  SetInfo(Index, TValue.From<TNullable<Variant>>(Value));
end;

{ TQryRecArray<T> }

constructor TQryRecArray<T>.Create;
begin
  inherited Create;
  FQryRecInfoList := TObjectList<T>.Create(True); // Owns objects
end;

destructor TQryRecArray<T>.Destroy;
begin
  FQryRecInfoList.Free;
  inherited;
end;

procedure TQryRecArray<T>.ClearFilter;
begin
  FFilterSQL := '';
end;

function TQryRecArray<T>.GetCount: Integer;
begin
  Result := FQryRecInfoList.Count;
end;

function TQryRecArray<T>.Rec(Index: Integer): T;
begin
  if (Index < 0) or (Index >= FQryRecInfoList.Count) then
    raise EORMUtilsException.CreateFmt('Index %d out of bounds.', [Index]);

  Result := FQryRecInfoList[Index];
end;

procedure TQryRecArray<T>.FetchAllInstance(DBConn: TUniConnection; const QryTxt: string);
var
  qr: TUniQuery;
  RecInstance: T;
  Ctx: TRttiContext;
  ObjType: TRttiType;
  Prop: TRttiProperty;
  Field: TField;
  ORMFieldName: string;
begin
  if not Assigned(DBConn) then
    raise EORMUtilsException.Create('Database connection (DBConn) is not assigned.');

  if Trim(QryTxt).IsEmpty then
    raise EORMUtilsException.Create('Query text (QryTxt) cannot be empty.');

  qr := TUniQuery.Create(nil);
  try
    qr.Connection := DBConn;
    qr.SpecificOptions.Values['FetchAll'] := 'True';
    qr.SpecificOptions.Values['CreateConnection'] := 'False';
    qr.SQL.Text := QryTxt;
    qr.Open;

    if qr.IsEmpty then
      Exit; // No records to fetch

    Ctx := TRttiContext.Create;
    ObjType := Ctx.GetType(T);

    try
      while not qr.Eof do
      begin
        RecInstance := T.Create;
        try
          // Iterate over each property of T and assign values from the query
          for Prop in ObjType.GetProperties do
          begin
            if not Prop.IsWritable then
              Continue;

            // Attempt to find the corresponding field in the query
            Field := qr.FindField(Prop.Name);
            if not Assigned(Field) then
              Continue; // Field not found, skip

            ORMFieldName := '_' + Prop.Name;

            // Handle TNullable<T> types
            if Prop.PropertyType.TypeKind = tkRecord then
            begin
              // Expecting TNullable<T>
              // Attempt to find the backing field for the nullable property
              if ObjType.GetField(ORMFieldName) = nil then
               Continue; // Backing field not found, skip

              if Prop.PropertyType.Name.StartsWith('TNullable<') then
              begin
                // Use RTTI to determine the generic type parameter
                if Field.IsNull then
                  ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), TValue.From<TNullable<Variant>>(NullValue))
                else
                begin
                  // Determine the generic type and set the value accordingly

                  if Prop.PropertyType.Name = 'TNullable<System.string>' then
                    ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), TValue.From<TNullable<string>>(Field.AsString))
                  else if Prop.PropertyType.Name = 'TNullable<System.Integer>' then
                    ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), TValue.From<TNullable<Integer>>(Field.AsInteger))
                  else if Prop.PropertyType.Name = 'TNullable<System.Int64>' then
                    ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), TValue.From<TNullable<Int64>>(Field.AsLargeInt))
                  else if Prop.PropertyType.Name = 'TNullable<System.Extended>' then
                    ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), TValue.From<TNullable<Extended>>(Field.AsFloat))
                  else if Prop.PropertyType.Name = 'TNullable<System.Currency>' then
                    ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), TValue.From<TNullable<Currency>>(Field.AsCurrency))
                  else if Prop.PropertyType.Name = 'TNullable<System.TDateTime>' then
                    ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), TValue.From<TNullable<TDateTime>>(Field.AsDateTime))
                  else if Prop.PropertyType.Name = 'TNullable<System.Boolean>' then
                    ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), TValue.From<TNullable<Boolean>>(Field.AsBoolean))
                  else if Prop.PropertyType.Name = 'TNullable<System.Variant>' then
                    ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), TValue.From<TNullable<Variant>>(Field.Value))
                  else
                    raise EORMUtilsException.CreateFmt('Unsupported TNullable type: %s', [Prop.PropertyType.Name]);
                end;
              end
              else
                raise EORMUtilsException.CreateFmt('Unsupported record type: %s', [Prop.PropertyType.Name]);
            end
            else
            begin
              // Handle non-nullable types
              case Prop.PropertyType.TypeKind of
                tkString, tkLString, tkWString, tkUString:
                  ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), Field.AsString);
                tkInteger:
                  ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), Field.AsInteger);
                tkInt64:
                  ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), Field.AsLargeInt);
                tkFloat:
                  if Prop.PropertyType.Handle = TypeInfo(Currency) then
                    ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), Field.AsCurrency)
                  else if Prop.PropertyType.Handle = TypeInfo(TDateTime) then
                    ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), Field.AsDateTime)
                  else
                    ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), Field.AsFloat);
                tkVariant:
                  ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), TValue.FromVariant(Field.AsVariant));
                tkEnumeration:
                  if Prop.PropertyType.Handle = TypeInfo(Boolean) then
                    ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), Field.AsBoolean)
                  else
                    ObjType.GetField(ORMFieldName).SetValue(Pointer(RecInstance), Field.AsString);
              else
                // Unsupported type; you can extend this as needed
                Continue;
              end;
            end;
          end;

          // Add the populated record to the list
          FQryRecInfoList.Add(RecInstance);
        except
          RecInstance.Free;
          raise; // Re-raise the exception after cleanup
        end;
        qr.Next;
      end;
    finally
      // No need to free TRttiContext as it's a record
    end;
  finally
    qr.Free;
  end;
end;

function TQryRecArray<T>.GetEnumerator: TEnumerator<T>;
begin
  Result := FQryRecInfoList.GetEnumerator;
end;

class function TQryRecArray<T>.FetchAll(DBConn: TUniConnection; const QryTxt: string): TQryRecArray<T>;
var
  Instance: TQryRecArray<T>;
begin
  Instance := TQryRecArray<T>.Create;
  try
    Instance.FetchAllInstance(DBConn, QryTxt);
    Result := Instance;
  except
    Instance.Free;
    raise;
  end;
end;

end.

-------------------------

unit ORM_CustomAttributes;

{$TYPEINFO ON}

interface

uses
  System.SysUtils, System.Classes, System.Rtti;

type
  TFormatType = (tiString, tiInteger, tiDate, tiDateTime, tiMoney, tiFloat, tiBoolean, tiByteArray, tiNone);

  /// <summary>
  /// Attribute to specify the database table associated with a class or field.
  /// </summary>
  TableAttribute = class(TCustomAttribute)
  private
    FTableName: string;
  public
    constructor Create(const ATableName: string);
    property TableName: string read FTableName;
  end;

  /// <summary>
  /// Attribute to mark a field as a primary key.
  /// </summary>
  PrimaryKeyAttribute = class(TCustomAttribute)
  public
    constructor Create;
  end;

  /// <summary>
  /// Attribute to specify the database column associated with a field.
  /// </summary>
  RefColumnAttribute = class(TCustomAttribute)
  private
    FColumnName: string;
  public
    constructor Create(const AColumnName: string);
    property ColumnName: string read FColumnName;
  end;

  /// <summary>
  /// Attribute to specify the formatting of a field.
  /// </summary>
  FmtPropAttribute = class(TCustomAttribute)
  private
    FFormatType: TFormatType;
  public
    constructor Create(AFormatType: TFormatType);
    property FormatType: TFormatType read FFormatType;
  end;

implementation

{ TableAttribute }

constructor TableAttribute.Create(const ATableName: string);
begin
  inherited Create;
  FTableName := ATableName;
end;

{ RefColumnAttribute }

constructor RefColumnAttribute.Create(const AColumnName: string);
begin
  inherited Create;
  FColumnName := AColumnName;
end;

{ PrimaryKeyAttribute }

constructor PrimaryKeyAttribute.Create;
begin
  inherited Create;
end;

{ FmtPropAttribute }

constructor FmtPropAttribute.Create(AFormatType: TFormatType);
begin
  inherited Create;
  FFormatType := AFormatType;
end;

end.

----------------------

unit pixel_classes;

interface

uses
 System.SysUtils, Rtti, TypInfo;

{$TYPEINFO ON}

type
 TZString = type string;

type
  TNullValue = record
  end;

  TNullable<T{: record}> = record
  public
    Value: T;
    HasValue: Boolean;

    class operator Implicit(const AValue: T): TNullable<T>;
    class operator Implicit(const AValue: TNullable<T>): T;
    class operator Implicit(const AValue: TNullValue): TNullable<T>;
    class operator Explicit(const AValue: T): TNullable<T>;

    // add these...
    class operator Equal(const A: TNullable<T>; const B: TNullValue): Boolean;
    class operator NotEqual(const A: TNullable<T>; const B: TNullValue): Boolean;
  end;

var NullValue: TNullValue;

implementation

class operator TNullable<T>.Implicit(const AValue: T): TNullable<T>;
begin
  Result.Value := AValue;
  Result.HasValue := True;
end;

class operator TNullable<T>.Implicit(const AValue: TNullable<T>): T;
begin
  if AValue.HasValue then
    Result := AValue.Value
  else
    Result := Default(T); // or raise an exception
end;

class operator TNullable<T>.Implicit(const AValue: TNullValue): TNullable<T>;
begin
  Result.Value := Default(T);
  Result.HasValue := False;
end;

class operator TNullable<T>.Explicit(const AValue: T): TNullable<T>;
begin
  Result.Value := AValue;
  Result.HasValue := True;
end;

class operator TNullable<T>.Equal(const A: TNullable<T>; const B: TNullValue): Boolean;
begin
  Result := not A.HasValue;
end;

class operator TNullable<T>.NotEqual(const A: TNullable<T>; const B: TNullValue): Boolean;
begin
  Result := A.HasValue;
end;

end.

-------------------------

In Delphi language, I have a TQryRecArray or its descendants, where  I want to map each property to a specific column of a TStringGrid. How can that be done? I need that when any property of a mapped class instance is changed, then the corresponding cell od the TStringGrid be updated accordingly, and when the contents of a TStringGrid Cell is changed, then the mapped class instance property is updated too.
Use RTTI do accomplish the task when appropriate.
Provide flexibility by avoiding hard-coded property accesses, making your solution more adaptable to different classes with similar structures.