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Serializer attributes

JsonFlow ships custom RTTI attributes (unit JsonFlow.Serializer.Attributes) that control how properties are serialized and deserialized. Attributes are applied only when TJSONSerializerOptions.ProcessAttributes is True (the default).

Available attributes​

[JSONIgnore]​

Excludes a property entirely from serialization and deserialization.

type
  TUser = class
  public
    Name: string;
    [JSONIgnore]
    InternalId: Integer; // not written to JSON, not read from JSON
  end;

[JSONName('key')]​

Maps a Delphi property to a different JSON key name.

type
  TProduct = class
  public
    [JSONName('product_name')]
    Name: string;
    [JSONName('unit_price')]
    Price: Double;
  end;

Result: {"product_name":"Widget","unit_price":9.99}

[JSONInclude(AIncludeNull, AIncludeEmpty)]​

Controls whether null or empty values are written to the output.

[JSONInclude(False, False)]
Description: string; // skipped when nil or empty

Default: both True.

[JSONDateTimeFormat('format')] or [JSONDateTimeFormat(AUseISO8601)]​

Overrides the DateTime serialization format for a specific property.

[JSONDateTimeFormat(True)]        // ISO 8601 (e.g., "2026-06-20T12:00:00")
CreatedAt: TDateTime;

[JSONDateTimeFormat('dd/MM/yyyy')]
BirthDate: TDateTime;

[JSONFloatFormat(ADecimalPlaces, AUseDecimalSeparator?)]​

Overrides the float format for a specific property.

[JSONFloatFormat(2)]         // 2 decimal places, use decimal separator (default True)
Price: Double;

[JSONFloatFormat(4, False)]  // 4 decimal places, no decimal separator
Rate: Double;

Constructor: Create(const ADecimalPlaces: Integer; const AUseDecimalSeparator: Boolean = True)

Attribute inheritance​

Attributes are read from the property definition on the class that declares it. Overriding a property in a subclass and re-applying a different attribute is supported.

Enabling attribute processing​

var
  LOptions: TJSONSerializerOptions;
begin
  LOptions := TJSONSerializerOptions.Default;
  LOptions.ProcessAttributes := True; // already True by default
  LSerializer := TJSONSerializer.Create(LOptions);
end;
note

Attributes require System.Rtti in the uses clause of the unit where they are declared. Delphi automatically includes RTTI for published properties; for public properties, ensure RTTI generation is enabled ({$RTTI EXPLICIT METHODS([]) FIELDS([]) PROPERTIES([vcPublic, vcPublished])}).