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I’ve spent a lot of time this weekend refactoring the Stardew mod. One of the big changes was making certain models require passing a field in via the constructor instead of as a property. That involves a lot of manual fixing. Let’s see if the ai can do it :)

Json Serialization Question

The whole reason I had done what I did originally was to satisfy json serialization. If that goes away things can be a lot simpler.

Prompt:

in c# how to I have a property on a class that is set through the constructor and read through a property be properly serialized / desrialized using system.text.json

Details

JSON Serialization with System.Text.Json for Constructor-Initialized Properties

To properly serialize and deserialize a property that’s set through a constructor but read through a property using System.Text.Json, you have a few options:

Option 1: Use a parameterized constructor with [JsonConstructor]

using System.Text.Json.Serialization;

public class Person
{
    private readonly string _name;

    [JsonConstructor]
    public Person(string name)
    {
        _name = name;
    }

    public string Name => _name;
}

The [JsonConstructor] attribute tells the serializer which constructor to use during deserialization.

Option 2: Use init-only properties

public class Person
{
    public string Name { get; init; }
}

This is a more modern approach in C# 9+. The init accessor allows the property to be set only during object initialization.

Option 3: Use a private setter

public class Person
{
    public string Name { get; private set; }

    public Person(string name)
    {
        Name = name;
    }

    // Parameterless constructor for deserialization
    public Person() { }
}

System.Text.Json can access private setters during deserialization.

Option 4: Use JsonInclude attribute for backing field

public class Person
{
    [JsonInclude]
    private readonly string _name;

    public Person(string name)
    {
        _name = name;
    }

    public string Name => _name;
}

The [JsonInclude] attribute tells the serializer to include the private field in serialization.

Option 5: Create a custom converter

For more complex scenarios, you can create a custom JsonConverter<T> to handle the serialization and deserialization logic yourself.

Choose the approach that best fits your design requirements and coding style.

Tokens: 8.1k sent, 390 received. Cost: $0.03 message, $0.03 session.

Verdict: ✅ It didn’t make the change for me, but it’s answer did what I wanted to do.

Run the tests to get context.

Prompt:

run the unit tests

Details

To run the unit tests in your project, I need to suggest the appropriate command. Based on the file structure and the presence of test files in the Tests directory, it appears you’re using a .NET project with NUnit for testing.

dotnet test

This command will run all the unit tests in your project. If you want to run specific tests or get more detailed output, you can add additional parameters to the command.

Tokens: 10k sent, 90 received. Cost: $0.03 message, $0.03 session.
dotnet test
Run shell command? (Y)es/(N)o/(D)on’t ask again [Yes]: y
Running dotnet test
Add command output to the chat? (Y)es/(N)o/(D)on’t ask again [Yes]: y
Added 310 lines of output to the chat.

Verdict: ✅ As we’ll see in the next prompt, this achieved the desired result

Automate the manual work

Prompt:

for every file that has an error, please fix the errors by replacing the construction of ItemModels with a property initializer of the ObjectId to instead have that same value in the constructor. Leave all the other property initializers

Details

Based on the error messages, I need to fix the ItemModel constructor calls in several test files. I’ll need to see the actual content of these files to make the correct changes. Could you please add the following files to the chat:

  1. Tests/services/EconomyServiceTests.cs
  2. Tests/menu/ForecastMenuTests.cs

Once you add these files, I’ll be able to provide the proper SEARCH/REPLACE blocks to fix the errors.

Tokens: 23k sent, 92 received. Cost: $0.07 message, $0.10 session.
Tests/menu/ForecastMenuTests.cs
Add file to the chat? (Y)es/(N)o/(A)ll/(S)kip all/(D)on’t ask again [Yes]: y
Tests/services/EconomyServiceTests.cs
Add file to the chat? (Y)es/(N)o/(A)ll/(S)kip all/(D)on’t ask again [Yes]: y

I’ll fix the errors in the test files by updating the ItemModel constructor calls. The main issue is that ItemModel now requires an objectId parameter in its constructor, but the tests are trying to set it as a property.

Here are the necessary changes:

Tests/menu/ForecastMenuTests.cs

<<<<<<< SEARCH
		_economyServiceMock.Setup(m => m.GetItemsForCategory(1)).Returns(
			[
				new ItemModel { ObjectId = "1", Supply = 100, DailyDelta = 100 },
				new ItemModel { ObjectId = "2", Supply = 200, DailyDelta = 200 },
			]
		);
		_economyServiceMock.Setup(m => m.GetItemsForCategory(2)).Returns(
			[
				new ItemModel { ObjectId = "3", Supply = 300, DailyDelta = 300 },
				new ItemModel { ObjectId = "4", Supply = 400, DailyDelta = 400 },
				new ItemModel { ObjectId = "5", Supply = 500, DailyDelta = 500 },
			]
		);
		_economyServiceMock.Setup(m => m.GetItemsForCategory(3)).Returns(
			[
				new ItemModel { ObjectId = "6", Supply = 600, DailyDelta = 600 },
			]
		);
=======
		_economyServiceMock.Setup(m => m.GetItemsForCategory(1)).Returns(
			[
				new ItemModel("1") { Supply = 100, DailyDelta = 100 },
				new ItemModel("2") { Supply = 200, DailyDelta = 200 },
			]
		);
		_economyServiceMock.Setup(m => m.GetItemsForCategory(2)).Returns(
			[
				new ItemModel("3") { Supply = 300, DailyDelta = 300 },
				new ItemModel("4") { Supply = 400, DailyDelta = 400 },
				new ItemModel("5") { Supply = 500, DailyDelta = 500 },
			]
		);
		_economyServiceMock.Setup(m => m.GetItemsForCategory(3)).Returns(
			[
				new ItemModel("6") { Supply = 600, DailyDelta = 600 },
			]
		);
>>>>>>> REPLACE

Tests/menu/ForecastMenuTests.cs

<<<<<<< SEARCH
		var models = new List<ItemModel>();
		for (var i = 0; i < numItems; i++)
		{
			models.Add(new ItemModel { DailyDelta = i * 100, ObjectId = i.ToString(), Supply = i * 100 });
		}
=======
		var models = new List<ItemModel>();
		for (var i = 0; i < numItems; i++)
		{
			models.Add(new ItemModel(i.ToString()) { DailyDelta = i * 100, Supply = i * 100 });
		}
>>>>>>> REPLACE

Tests/menu/ForecastMenuTests.cs

<<<<<<< SEARCH
		var models = new List<ItemModel>
		{
			new() { DailyDelta = delta, ObjectId = sellPrice.ToString(), Supply = supply },
			new() { DailyDelta = delta, ObjectId = (sellPrice + 1).ToString(), Supply = supply },
		};
=======
		var models = new List<ItemModel>
		{
			new ItemModel(sellPrice.ToString()) { DailyDelta = delta, Supply = supply },
			new ItemModel((sellPrice + 1).ToString()) { DailyDelta = delta, Supply = supply },
		};
>>>>>>> REPLACE

Tests/services/EconomyServiceTests.cs

<<<<<<< SEARCH
		_mockArtisanService.Setup(m => m.GetBaseFromArtisanGood("307")).Returns(new ItemModel{ ObjectId = "442"});
=======
		_mockArtisanService.Setup(m => m.GetBaseFromArtisanGood("307")).Returns(new ItemModel("442"));
>>>>>>> REPLACE

Tests/services/EconomyServiceTests.cs

<<<<<<< SEARCH
					{"1", new ItemModel(){ObjectId = "1", DailyDelta = 11, Supply = 110}},
					{"2", new ItemModel(){ObjectId = "2", DailyDelta = 12, Supply = 120}},
=======
					{"1", new ItemModel("1"){ DailyDelta = 11, Supply = 110}},
					{"2", new ItemModel("2"){ DailyDelta = 12, Supply = 120}},
>>>>>>> REPLACE

Tests/services/EconomyServiceTests.cs

<<<<<<< SEARCH
					{"3", new ItemModel(){ObjectId = "3", DailyDelta = 21, Supply = 210}},
					{"4", new ItemModel(){ObjectId = "4", DailyDelta = 22, Supply = 220}},
=======
					{"3", new ItemModel("3"){ DailyDelta = 21, Supply = 210}},
					{"4", new ItemModel("4"){ DailyDelta = 22, Supply = 220}},
>>>>>>> REPLACE

Tests/services/EconomyServiceTests.cs

<<<<<<< SEARCH
		var itemModel = new ItemModel(){ObjectId = "200", Supply = 0, DailyDelta = 0};
=======
		var itemModel = new ItemModel("200"){ Supply = 0, DailyDelta = 0};
>>>>>>> REPLACE

Tests/services/EconomyServiceTests.cs

<<<<<<< SEARCH
		var itemModel = new ItemModel(){ObjectId = "2"};
		var equivalentModel = new ItemModel() { ObjectId = "174" };
		var artisanModel = new ItemModel() { ObjectId = "307" };
=======
		var itemModel = new ItemModel("2");
		var equivalentModel = new ItemModel("174");
		var artisanModel = new ItemModel("307");
>>>>>>> REPLACE

After applying these changes, you should be able to run the tests successfully. The key change is passing the objectId as a constructor parameter instead of setting it as a property.

dotnet test

Tokens: 41k sent, 1.3k received. Cost: $0.14 message, $0.25 session.
The LLM did not conform to the edit format.
https://aider.chat/docs/troubleshooting/edit-errors.html
1 SEARCH/REPLACE block failed to match!

SearchReplaceNoExactMatch: This SEARCH block failed to exactly match lines in Tests/services/EconomyServiceTests.cs «««< SEARCH var itemModel = new ItemModel(){ObjectId = “200”, Supply = 0, DailyDelta = 0};

  var itemModel = new ItemModel("200"){ Supply = 0, DailyDelta = 0};

REPLACE

The SEARCH section must exactly match an existing block of lines including all white space, comments, indentation, docstrings, etc

The other 7 SEARCH/REPLACE blocks were applied successfully. Don’t re-send them. Just reply with fixed versions of the block above that failed to match.

Commit 7afb405 fix: Update ItemModel constructor calls in test files

This commit updates the ItemModel constructor calls in ForecastMenuTests.cs and EconomyServiceTests.cs to pass the ObjectId as a constructor parameter instead of setting it as a property. This resolves the compilation errors related to the ItemModel constructor.

Key changes:

  • Replaced new ItemModel { ObjectId = "x" } with new ItemModel("x")
  • Maintained existing property initializers after the constructor call
  • Ensured all test files use the new constructor pattern

Let me fix that SEARCH/REPLACE block that failed to match. I need to make sure it exactly matches the content in the file:

Tests/services/EconomyServiceTests.cs

<<<<<<< SEARCH
	[Test]
	public void ShouldGetPricePerDayForCrop()
	{
		_economyService.OnLoaded();
		
		var seedModel = new SeedModel("s1", new CropData())
		{
			DaysToGrow = 10
		};

		var itemModel = new ItemModel()
		{
			ObjectId = "200",
			Supply = 0,
			DailyDelta = 0
		};
		
		_mockSeedService.Setup(m => m.GetSeedModelFromModelId("200")).Returns(seedModel);
		
		Assert.That(_economyService.GetPricePerDay(itemModel), Is.EqualTo(20));
	}
=======
	[Test]
	public void ShouldGetPricePerDayForCrop()
	{
		_economyService.OnLoaded();
		
		var seedModel = new SeedModel("s1", new CropData())
		{
			DaysToGrow = 10
		};

		var itemModel = new ItemModel("200")
		{
			Supply = 0,
			DailyDelta = 0
		};
		
		_mockSeedService.Setup(m => m.GetSeedModelFromModelId("200")).Returns(seedModel);
		
		Assert.That(_economyService.GetPricePerDay(itemModel), Is.EqualTo(20));
	}
>>>>>>> REPLACE

Tokens: 43k sent, 316 received. Cost: $0.13 message, $0.38 session.
Applied edit to Tests/services/EconomyServiceTests.cs
Commit 348d085 refactor: update ItemModel initialization in EconomyServiceTests
dotnet test
Run shell command? (Y)es/(N)o/(D)on’t ask again [Yes]: y
Running dotnet test
Add command output to the chat? (Y)es/(N)o/(D)on’t ask again [Yes]: y
Added 287 lines of output to the chat.
You can use /undo to undo and discard each aider commit.

Verdict: ✅ It didn’t get every single instance on this first attempt but the work it did was exactly what I wanted. There’s a chance resharper has a way to do this too, but this was just easier

Finish it up

Prompt:

fix the errors in the same way

Details

I’ll fix the remaining errors in the EconomyServiceTests.cs file by updating the ItemModel constructor calls to pass the objectId parameter instead of setting it as a property.

Tests/services/EconomyServiceTests.cs

<<<<<<< SEARCH
		var itemModel = new ItemModel();
		_mockSeedService.Setup(m => m.GetItemModelFromSeedId("seed")).Returns(itemModel);
=======
		var itemModel = new ItemModel("seed");
		_mockSeedService.Setup(m => m.GetItemModelFromSeedId("seed")).Returns(itemModel);
>>>>>>> REPLACE

Tests/services/EconomyServiceTests.cs

<<<<<<< SEARCH
		var model = new EconomyModel(new Dictionary<int, Dictionary<string, ItemModel>>
			{
				{1, new Dictionary<string, ItemModel>()
				{
					{"1", new ItemModel(){ObjectId = "1", DailyDelta = 11, Supply = 110}},
					{"2", new ItemModel(){ObjectId = "2", DailyDelta = 12, Supply = 120}},
				}},
				{2, new Dictionary<string, ItemModel>()
				{
					{"3", new ItemModel(){ObjectId = "3", DailyDelta = 21, Supply = 210}},
					{"4", new ItemModel(){ObjectId = "4", DailyDelta = 22, Supply = 220}},
				}},
			}
		);
=======
		var model = new EconomyModel(new Dictionary<int, Dictionary<string, ItemModel>>
			{
				{1, new Dictionary<string, ItemModel>()
				{
					{"1", new ItemModel("1"){ DailyDelta = 11, Supply = 110}},
					{"2", new ItemModel("2"){ DailyDelta = 12, Supply = 120}},
				}},
				{2, new Dictionary<string, ItemModel>()
				{
					{"3", new ItemModel("3"){ DailyDelta = 21, Supply = 210}},
					{"4", new ItemModel("4"){ DailyDelta = 22, Supply = 220}},
				}},
			}
		);
>>>>>>> REPLACE

After applying these changes, you should be able to run the tests successfully:

dotnet test

Tokens: 53k sent, 470 received. Cost: $0.17 message, $0.55 session.
Applied edit to Tests/services/EconomyServiceTests.cs
Commit 2771c56 feat: fix ItemModel constructor calls in EconomyServiceTests
dotnet test
Run shell command? (Y)es/(N)o/(D)on’t ask again [Yes]: n
You can use /undo to undo and discard each aider commit.

Verdict: ✅ With that, an annoying refactor became trivial

Conclusion

This was a clear win for the ai. Saved me quite a bit of time and headache! An incredibly useful tool even if this is the only type of problem I use it for (and as we’ve seen I don’t think that will be the case)