How to return JSON in a C# API

Question

I'm new to C# and I'm wondering how would one go about casting a stringbuilder to a JSON structure? I'm using SQL's FOR JSON feature and it returns JSON in multiple rows. I add the rows together to get a string and cast it to JSON this way. I'm getting this error when I compile however this was the closest solution I found. It seems like C# is pretty strict with data types

Error Argument 1: cannot convert from 'System.Text.StringBuilder' to 'System.ReadOnlySpan' WebApiSwagger

public class AlgReadingChannel
{
     /// <example>1</example>
     [Required]
     public int chanNo { get; set; }
}


public class AlgReadingInner
{
    /// <example>2020-03-12T16:41:43.017</example>
    public string Created { get; set; }
    /// <example>2020-03-12T16:41:43.017</example>
    public string Modified { get; set; }
    /// <example>24867</example>
    public int ReadingID { get; set; }
    /// <example>2323</example>
    public string Name { get; set; }
    /// <example>Starting</example>
    public string Reading { get; set; }
    /// <example></example>
    public string State { get; set; }
    /// <example>X</example>
    public string Site { get; set; }
    /// <example>Main</example>
    [Required]
    public IList<AlgReadingChannel> v { get; set; }
}

/// <summary>
/// Represents AlgReading parent class
/// </summary>
public class AlgReadingOuter
{
    /// <example>5137</example>
    [Required]
    public int AnalogID { get; set; }
    /// <example>E360EC39-7B0F-42A1-B125-2298SHDE53</example>
    [Required]
    public string SiteID { get; set; }
    /// <example>2020-03-12T09:41:43</example>
    [Required]
    public string EntryDateTime { get; set; }
    [Required]
    public IList<AlgReadingInner> t { get; set; }
}

var stringBuilder = new StringBuilder();
var docs = new List<AlgReadingOuter>();

stringBuilder.Append([{
    "AnalogID": 5137,
    "SiteID": "E360EC39-7B0F-42A1-B125-22C1F6C5DE53",
    "EntryDateTime": "2020-03-12T09:41:43",
    "t": [{
        "Created": "2020-03-12T16:41:43.017",
        "Modified": "2020-03-12T16:41:43.017",
        "ReadingID": 24867,
        "Name": "ABC",
        "Reading": "Starting",
        "State": "X",
        "Site": "Main",
        "v": [{
            "chanNo": 1
        }]
    },
    {
        "Created": "2020-03-12T16:41:43.017",
        "Modified": "2020-03-12T16:41:43.017",
        "ReadingID": 24868,
        "Name": "bar",
        "Reading": "Starting",
        "State": "X",
        "Site": "Main",
        "v": [{
            "chanNo": 2
        }]
    },
    {
        "Created": "2020-03-12T16:41:43.017",
        "Modified": "2020-03-12T16:41:43.017",
        "ReadingID": 24869,
        "Name": "foo",
        "Reading": "Starting",
        "State": "X",
        "Site": "Main",
        "v": [{
            "chanNo": 3
        }]
    },
    {
        "Created": "2020-03-12T16:41:43.017",
        "Modified": "2020-03-12T16:41:43.017",
        "ReadingID": 24870,
        "Name": "Test",
        "Reading": "Starting",
        "State": "X",
        "Site": "Aux",
        "v": [{
            "chanNo": 4
        }]
    },
    {
        "v": [{
            "chanNo": 30
        },
        {
            "chanNo": 32
        },
        {
            "chanNo": 39
        },
        {
            "chanNo": 56
        },
        {
            "chanNo": 69
        },
        {
            "chanNo": 71
        },
        {
            "chanNo": 79
        },
        {
            "chanNo": 82
        },
        {
            "chanNo": 87
        }]
    }]
}]);

var algReading = JsonSerializer.Deserialize<AlgReadingOuter>(stringBuilder);
docs.Add(algReading);

bolkay · Accepted Answer · 2020-04-02 18:46:08Z

2

That is because StringBuilder is not a string.

You should call ToString() to actually get what you want.

So, it should really be:

algReading= JsonSerializer.Deserialize<AlgReadingOuter>(jsonResult.ToString());

answered Apr 2, 2020 at 18:46

bolkay

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5 Comments

node943034835 Over a year ago

I think you're correct however this leads to another error about JSON not matching the swagger model. "The JSON value could not be converted to WebApiSwagger.Api.v2.Models.AlgReadingOuter. Path: $ | LineNumber: 0 | BytePositionInLine: 1.". Do you know of an easy way to return the JSON other than that way I'm trying above? All I'm doing is a SQL query and trying to return the results.

bolkay Over a year ago

Ensure your json is correct. I suggest streaming from a text file.

node943034835 Over a year ago

I'm sure it's correct. I think it's having issues being serialized to the nested list constructor. I even used a generator such as json2csharp.com and it kicked back as unable to convert. pastebin.com/8wBcwYq8

bolkay Over a year ago

I pasted your json into json2csharp and it works. Don't know if it counts, but you could mark the date properties as DateTime instead of string.

node943034835 Over a year ago

So it was throwing errors coercing to the class structure as it was hard coded. So I changed the deserialization syntax to not have a structure to use as a template. I'm still unsure why that did the fix because the structure looked 1:1. That fixed it though! return Ok(JsonConvert.DeserializeObject(jsonResult.ToString()));

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