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Composer — dynamic editing

TJSONComposer (unit JsonFlow.Composer) provides an in-place, fluent API for building and mutating JSON structures. It implements IJSONComposer.

Building JSON from scratch​

uses
  JsonFlow.Composer,
  JsonFlow.Interfaces;

var
  LComposer: TJSONComposer;
begin
  LComposer := TJSONComposer.Create;
  try
    LComposer
      .BeginObject
        .Add('name', 'Alice')
        .Add('age', 28)
        .Add('active', True)
        .BeginArray('tags')
          .Add('', 'dev')
          .Add('', 'lead')
        .EndArray
      .EndObject;

    WriteLn(LComposer.AsJSON);
  finally
    LComposer.Free;
  end;
end;

Loading and mutating existing JSON​

LComposer := TJSONComposer.Create;
try
  LComposer.LoadJSON('{"user":{"name":"Bob","age":25},"tags":["dev"]}');

  // Dot-notation path for nested access
  LComposer.SetValue('user.age', 26);
  LComposer.AddToArray('tags', 'lead');
  LComposer.RemoveKey('user.name');

  WriteLn(LComposer.AsJSON);
finally
  LComposer.Free;
end;

Array manipulation​

// Add single value
LComposer.AddToArray('items', 42);

// Add element (IJSONElement)
LComposer.AddToArray('items', LElement);

// Add multiple values
LComposer.AddToArray('items', TArray<Variant>.Create(1, 2, 3));

// Merge values into existing array
LComposer.MergeArray('items', TArray<Variant>.Create(4, 5));

// Remove by index
LComposer.RemoveFromArray('items', 0);

// Replace entire array content
LComposer.ReplaceArray('items', TArray<Variant>.Create(10, 20));

Nested object manipulation​

// Add a named sub-object at path
LComposer.AddObject('user', 'address');

// Embed raw JSON at a key
LComposer.AddJSON('meta', '{"version":2}');

Convenience value methods​

LComposer
  .StringValue('city', 'Berlin')
  .NumberValue('lat', 52.52)
  .IntegerValue('zoom', 14)
  .BooleanValue('visible', True)
  .NullValue('extra')
  .DateTimeValue('created', Now);

Callback-style nested builders​

LComposer.ObjectValue('address',
  procedure(const B: IJSONComposer)
  begin
    B.Add('street', 'Main St')
     .Add('zip', '10115');
  end
);

LComposer.ArrayValue('scores',
  procedure(const B: IJSONComposer)
  begin
    B.Add('', 10).Add('', 20).Add('', 30);
  end
);
// Navigate to a path for subsequent Add calls (context-aware)
LComposer.NavigateTo('user.address');
LComposer.GetCurrentPath; // returns 'user.address'
LComposer.GetContextInfo; // returns TContextInfo record

Debug mode​

LComposer.EnableDebugMode(True);
// ... operations ...
for var LStep in LComposer.GetCompositionTrace do
  WriteLn(LStep);

Output methods​

MethodDescription
AsJSON(AIdent)Returns compact or indented JSON string
ToJSON(AIdent)Alias for AsJSON
ToElementReturns the root IJSONElement
GetRootReturns the root IJSONElement

Merging​

// Merge another IJSONElement into the composer root
LComposer.Merge(LExtraElement);

Cloning and clearing​

LClone := LComposer.Clone;   // deep copy
LComposer.Clear;             // reset to empty

TJSONNavigator — read-only path access​

For read-only navigation, use TJSONNavigator directly:

uses
  JsonFlow.Navigator;

var
  LNav: TJSONNavigator;
begin
  LNav := TJSONNavigator.Create(LComposer.GetRoot);
  try
    WriteLn(LNav.GetString('user.name'));
    WriteLn(LNav.GetInteger('user.age'));
    WriteLn(BoolToStr(LNav.GetBoolean('active'), True));
    WriteLn(BoolToStr(LNav.IsNull('extra'), True));
  finally
    LNav.Free;
  end;
end;

TJSONNavigator supports dot-notation and array index notation (tags[0]).