Working with JSON files in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Working with JSON files

Start Program

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Read JSON File

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Parse JSON to Object

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Use Object Data

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Modify Object (optional)

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Serialize Object to JSON

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Write JSON to File

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End Program

The program reads a JSON file, converts it to an object, optionally modifies it, then writes it back as JSON.

Execution Sample

C Sharp (C#)

using System.Text.Json;

string json = File.ReadAllText("data.json");
var person = JsonSerializer.Deserialize<Person>(json);
person.Age += 1;
string newJson = JsonSerializer.Serialize(person);
File.WriteAllText("data.json", newJson);

This code reads a JSON file, deserializes it into a Person object, increases the age by 1, then writes the updated JSON back.

Execution Table

Step	Action	Code Line	Variable State	Output/File Content
1	Read JSON file content	string json = File.ReadAllText("data.json");	json = '{"Name":"Alice","Age":30}'	File content read as string
2	Deserialize JSON to Person object	var person = JsonSerializer.Deserialize<Person>(json);	person = Person{Name="Alice", Age=30}	No output
3	Increase person's age by 1	person.Age += 1;	person = Person{Name="Alice", Age=31}	No output
4	Serialize Person object to JSON string	string newJson = JsonSerializer.Serialize(person);	newJson = '{"Name":"Alice","Age":31}'	No output
5	Write updated JSON string to file	File.WriteAllText("data.json", newJson);	person unchanged	File content updated to '{"Name":"Alice","Age":31}'
6	End program	End	person unchanged	File saved with updated JSON

💡 Program ends after writing updated JSON back to file.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	Final
json	null	{"Name":"Alice","Age":30}	{"Name":"Alice","Age":30}	{"Name":"Alice","Age":30}	{"Name":"Alice","Age":30}	{"Name":"Alice","Age":30}	{"Name":"Alice","Age":30}
person	null	null	Person{Name="Alice", Age=30}	Person{Name="Alice", Age=31}	Person{Name="Alice", Age=31}	Person{Name="Alice", Age=31}	Person{Name="Alice", Age=31}
newJson	null	null	null	null	{"Name":"Alice","Age":31}	{"Name":"Alice","Age":31}	{"Name":"Alice","Age":31}

Key Moments - 3 Insights

Why do we need to deserialize JSON before using it?

Because JSON is a text format, deserialization converts it into a C# object we can work with, as shown in step 2 of the execution_table.

What happens if we forget to write the updated JSON back to the file?

The file will not reflect changes made to the object in memory. Step 5 shows writing back is necessary to save changes.

Why do we serialize the object again before writing to the file?

Serialization converts the C# object back into JSON text format, which is needed to save it as a file, as shown in step 4.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'person.Age' after step 3?

A 31

B 30

C 29

D null

💡 Hint

Check the 'Variable State' column at step 3 in the execution_table.

At which step is the JSON string first read from the file?

A Step 2

B Step 4

C Step 1

D Step 5

💡 Hint

Look at the 'Action' column to find when the file content is read.

If we skip serialization (step 4), what will happen when writing to the file in step 5?

A The file will be empty

B The file will contain the object directly (invalid format)

C The file will contain the old JSON

D The program will crash

💡 Hint

Consider what File.WriteAllText expects as input and what happens if we pass an object instead of a string.

Concept Snapshot

Working with JSON files in C#:
- Read JSON text from file with File.ReadAllText
- Convert JSON text to object using JsonSerializer.Deserialize<T>
- Modify object properties as needed
- Convert object back to JSON text with JsonSerializer.Serialize
- Write JSON text back to file with File.WriteAllText
Always deserialize before use and serialize before saving.

Full Transcript

This example shows how to work with JSON files in C#. First, the program reads the JSON content from a file as a string. Then it converts this JSON string into a C# object using deserialization. After that, it modifies the object's data, for example increasing the age by one. Next, it converts the updated object back into a JSON string by serialization. Finally, it writes this new JSON string back to the file, saving the changes. This process ensures that the program can read, use, and update JSON data stored in files.