Deserializing values I need from large JSON using System.Text.Json Utf8JsonReader

Question

I'm trying to do the following..

Not represent JSON in a POCO

Find and Deserialize only the value of a particular property hidden deep within a large JSON using Utf8JsonReader.

Filter for JSON tokens : working

Following is the code that is working.

using System;
using System.IO;
using System.Text;
using System.Text.Json;
namespace ProcessData
{
    class Program
    {

        private static readonly byte[] s_pagetypeUtf8 = Encoding.UTF8.GetBytes("type");
        private static readonly byte[] s_transactionorderidUtf8 = Encoding.UTF8.GetBytes("orderid");
        private static readonly byte[] s_transactionorderamountUtf8 = Encoding.UTF8.GetBytes("amount_to_pay");

static void Main(string[] args)
        {
            string fileName = "D:\\500GBNP\\Projects\\temp1\\temp1.json";
            using var fs = new FileStream(fileName, FileMode.Open, FileAccess.Read);
            using var sr = new StreamReader(fs, Encoding.UTF8);
            string line = String.Empty;
            bool success =false;
            string orderid="";
            decimal orderamount=0;
            while ((line = sr.ReadLine()) != null)
                {
                    ReadOnlySpan<byte> jsonReadOnlySpan = Encoding.UTF8.GetBytes(line);
            
                    var reader = new Utf8JsonReader(jsonReadOnlySpan);

                    while (reader.Read())
                    {
                        JsonTokenType tokenType = reader.TokenType;

                        switch (tokenType)
                        {
                            case JsonTokenType.PropertyName:
                                if (reader.ValueTextEquals(s_pagetypeUtf8))
                                {
                                    // Assume valid JSON, known schema
                                    reader.Read();
                                    if (reader.GetString().Equals("Success Confirmation"))
                                    {
                                        success=true;
                                        
                                    
                                    }
                                }
                                break;
                        }
                    }
                }
            Console.WriteLine($"{success}");
        }

    }
}

The json file contains the following text and is successfully able to find if the line contains page type value Success Confirmation :

{"contexts":{"page":{"type":"Success Confirmation"},"transaction":{"orderid":100002210,"shipping_cost":70,"subtotal":200,"subtotal_incl_tax":200,"tax_cost":0,"amount_to_pay":270,"delivery":{"postcode":"400666","state":"West Bengal","city":"kolkata","country":"IN"},"billing":{"postcode":"400666","state":"West Bengal","city":"kolkata","country":"IN"},"product_details":{"no_of_items":1,"order_items":[{"name":"Designer Red Folral Earrings with White Beads","id":5384,"quantity":1,"price":200,"tax":0,"price_incl_tax":200,"actual_price":400,"percent_discount":50,"category":["New Arrivals","Modern Jewellery","Women","Earrings & Studs","Earrings & Studs","Danglers","View All","Hot Deals","Puja Collection 2016"]}]},"payment_mathod":"Cash On Delivery"}}

What I need to do is if page type is Success Confirmation, get the value of orderid and amount_to_pay. This is where I'm getting stuck.

I tried the following..

if (reader.GetString().Equals("Success Confirmation"))
                                    {
                                        success=true;
                                        reader.Read(); 
                                        if (reader.TokenType == JsonTokenType.EndObject)
                                            {
                                                break;
                                            }
                                            reader.Read();
                                        if (reader.ValueTextEquals(s_transactionorderidUtf8))
                                            {
                                                reader.Read();
                                                orderid=reader.GetString();
                                            }

                                        if (reader.ValueTextEquals(s_transactionorderamountUtf8))
                                            {
                                                reader.Read();
                                                orderamount=reader.GetDecimal();
                                            }
                                    Console.WriteLine($"{orderid}:{orderamount}");
                                    
                                    }

Without the if (reader.TokenType == JsonTokenType.EndObject) codeblock, it throws an error

> Cannot compare the value of a token type 'EndObject' to text.

With the code block it just moves forward

Any help is sincerely appreciated.

Please do ask if I have not been able to explain or you need any further info.

Thanks

Answer 1

What I need to do is if page type is Success Confirmation, get the value of orderid and amount_to_pay.

I think you're overthinking it. You could just map the classes:

class Order {
    public Context contexts { get;set;}
};

class Context {
    public Page page {get; set;}
    public Transaction transaction {get; set;}
}

class Page {
    public string type {get; set;}
}

class Transaction 
{
    public long orderid {get;set;}
    public decimal amount_to_pay {get;set;}
}

Then with

var o = JsonSerializer.Deserialize<Order>(json);

Console.WriteLine(o.contexts.page.type);
Console.WriteLine(o.contexts.transaction.orderid);
Console.WriteLine(o.contexts.transaction.amount_to_pay);

the result is:

Success Confirmation
100002210
270

Option B. With JsonDocument

If you don't wish to create classes then you can use JsonDocument.

using JsonDocument doc = JsonDocument.Parse(json);

var context = doc.RootElement.GetProperty("contexts");
Console.WriteLine(context.GetProperty("page").GetProperty("type").GetString());
Console.WriteLine(context.GetProperty("transaction").GetProperty("orderid").GetUInt64());
Console.WriteLine(context.GetProperty("transaction").GetProperty("amount_to_pay").GetDecimal());

Result:

Success Confirmation
100002210
270