JsonObjectArrayUpdater.h

Go to the documentation of this file.

// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreMinimal.h"
#include "Dom/JsonObject.h"
#include "Dom/JsonValue.h"
 
template <typename ElementType, typename KeyType>
struct FJsonObjectArrayUpdater
{
    DECLARE_DELEGATE_RetVal_OneParam(KeyType, FGetElementKey, const ElementType&);
 
    DECLARE_DELEGATE_RetVal_TwoParams(bool, FTryGetJsonObjectKey, const FJsonObject&, KeyType& /*OutKey*/);
 
    DECLARE_DELEGATE_TwoParams(FUpdateJsonObject, const ElementType&, FJsonObject&);
 
    DECLARE_DELEGATE_OneParam(FSortArray, TArray<TSharedPtr<FJsonValue>>&);
 
    static void Execute(FJsonObject& JsonObject, const FString& ArrayName, const TArray<ElementType>& SourceArray, FGetElementKey GetElementKey, FTryGetJsonObjectKey TryGetJsonObjectKey, FUpdateJsonObject UpdateJsonObject, FSortArray SortJsonArray = FSortArray())
    {
        if (SourceArray.Num() > 0)
        {
            TArray<TSharedPtr<FJsonValue>> NewJsonValues;
            {
                const TArray<TSharedPtr<FJsonValue>>* ExistingJsonValues;
                if (JsonObject.TryGetArrayField(ArrayName, ExistingJsonValues))
                {
                    // Build a map of elements for quick access and to keep track of which ones got updated
                    TMap<KeyType, const ElementType*> ElementsMap;
                    for (const ElementType& Element : SourceArray)
                    {
                        ElementsMap.Add(GetElementKey.Execute(Element), &Element);
                    }
 
                    // Update existing json values and discard entries that no longer exist or are invalid
                    for (TSharedPtr<FJsonValue> ExistingJsonValue : *ExistingJsonValues)
                    {
                        const TSharedPtr<FJsonObject>* ExistingJsonValueAsObject;
                        if (ExistingJsonValue->TryGetObject(ExistingJsonValueAsObject))
                        {
                            KeyType ElementKey;
                            if (TryGetJsonObjectKey.Execute(**ExistingJsonValueAsObject, ElementKey))
                            {
                                if (const ElementType** ElementPtr = ElementsMap.Find(ElementKey))
                                {
                                    UpdateJsonObject.Execute(**ElementPtr, **ExistingJsonValueAsObject);
                                    NewJsonValues.Add(ExistingJsonValue);
                                    ElementsMap.Remove(ElementKey);
                                }
                            }
                        }
                    }
 
                    // Add new elements
                    for (auto It = ElementsMap.CreateConstIterator(); It; ++It)
                    {
                        TSharedPtr<FJsonObject> NewJsonObject = MakeShareable(new FJsonObject);
                        UpdateJsonObject.Execute(*It.Value(), *NewJsonObject.Get());
                        NewJsonValues.Add(MakeShareable(new FJsonValueObject(NewJsonObject)));
                    }
                }
                else
                {
                    // Array doesn't exist in the given JsonObject, so build a new array
                    for (const ElementType& Element : SourceArray)
                    {
                        TSharedPtr<FJsonObject> NewJsonObject = MakeShareable(new FJsonObject);
                        UpdateJsonObject.Execute(Element, *NewJsonObject.Get());
                        NewJsonValues.Add(MakeShareable(new FJsonValueObject(NewJsonObject)));
                    }
                }
            }
 
            // Optionally sort new json array before setting incase the user doesn't want the default
            // appending of new items at the end.
            SortJsonArray.ExecuteIfBound(NewJsonValues);
 
            // Set the new content of the json array
            JsonObject.SetArrayField(ArrayName, NewJsonValues);
        }
        else
        {
            // Source array is empty so remove the json array
            JsonObject.RemoveField(ArrayName);
        }
    }
};