Formatting api JSON response to add attributes to an array

Question

I have the following api controller that returns a json representation of the query you see here:

public async Task<ActionResult<IEnumerable<CarDto>>> GetCarData(Guid carID)
{
    var carData = await (from cl in _context.CarList
                         join tl in _context.transmissionList
                             on cl.CId equals tl.CId
                         join to in _context.transmissionOptions
                             on tl.TId equals to.TId
                         where cl.CId == carID
                         select new CarDto
                         {
                             CarId = cl.CarId,
                             TransmissionId = tl.TId,
                             OptionId = to.OptionId,
                             GearId = to.GearId
                         })
                         .ToListAsync();
    return carData;
}

The returned json data looks like this:

[
    {
        "carId": "351a",
        "transmissionId": "ec7",
        "optionId": "a1",
        "gearId": "674532a"
    },
    {
        "carId": "351a",
        "transmissionId": "ec7",
        "optionId": "b7",
        "gearId": "5f9173f"
    },
    {
        "carId": "351a",
        "transmissionId": "ec7",
        "optionId": "c5",
        "gearId": "cf807"
    }
]

However, I'd like for it to be formatted such that there is a property called transmissionChoices that contains an array of the possible options.

Like this:

{
    "carId": "351a",
    "transmissionId": "ec7",
    "transmissionChoices": [
        {
            "optionId": "a1",
            "gearId": "674532a"
        },
        {
            "optionId": "b7",
            "gearId": "5f9173f"
        },
        {
            "optionId": "c5",
            "gearId": "cf807"
        }
    ]
}

Is there a way to get the controller to format it like that?

Tom Faltesek · Accepted Answer · 2019-11-06 21:43:31Z

1

You can use the LINQ GroupBy method and then project the grouped results into the shape you want.

public async Task<ActionResult<IEnumerable<object>>> GetCarData(Guid carID)
{
    var carData = await (from cl in _context.CarList
                        join tl in _context.transmissionList
                            on cl.CId equals tl.CId
                        join to in _context.transmissionOptions
                            on tl.TId equals to.TId
                        where cl.CId == carID
                        select new
                        {
                            CarId = cl.CarId,
                            TransmissionId = tl.TId,
                            OptionId = to.OptionId,
                            GearId = to.GearId
                        })
                        .GroupBy(x => x.CarId)
                        .Select(g => new
                        {
                            CarId = g.First().CarId,
                            TransmissionId = g.First().TransmissionId,
                            TransmissionChoices = g.Select(x => new
                            {
                                OptionId = x.OptionId,
                                GearId = x.GearId
                            })
                        })
                        .ToListAsync();
    return carData;
}

Note that this is projecting the results into an anonymous type. Feel free to create a model that matches the schema you need and then use that model in the Select(...) projection.

edited Nov 6, 2019 at 21:43

answered Nov 6, 2019 at 21:36

Tom Faltesek

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2 Comments

SkyeBoniwell Over a year ago

Hi, thanks! So would this require 2 models? My original one, CarDto, and a new one? Or would it be best to combine the two? Thanks again!

Tom Faltesek Over a year ago

It's up to you. There's no real reason to have a defined model for the first projection since that type is not exposed by your API. I would probably just change the shape of your CarDto class to match your intended output. You'll probably want to add a TransmissionChoiceDto or something for the nested collection of { optionId; gearId; }.

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