The process cannot access the file because it is being used by another process --- EF Core serializing XML - filestream

Question

I am trying to write a method to fetch the categories and their respective products from the Northwind database and to then use xml serialization to write to a file.
I have tried the following code but get the error detailed in the heading. (The file is created but no XML is written to it).
Is anyone able to advise what is wrong with my code ? Any assistance would be greatly appreciated. Thank you.
static async void SerializeCategoriesWithXML() {
FileStream xmlFileStream = null;
XmlWriter xml = null;
// Create file to write to :
string path = Combine(CurrentDirectory, "CategoriesAndTheirProducts.xml");
// Create a file stream :
xmlFileStream = File.Create(path);
// Wrap the file stream in an Xml writer helper and automatically indent the nested elements :
xml = XmlWriter.Create(xmlFileStream, new XmlWriterSettings { Indent = true });
using (var db = new NorthwindContext())
{
// A query to get all categories and their related products :
IQueryable<Categories> cats = db.Categories
.Include(c => c.Products
.ToList());
await using (FileStream stream = File.Create(path))
{
// Write the Xml declaration :
xml.WriteStartDocument();
// Serialize the object graph to the stream :
foreach (Categories c in cats)
{
// Write a root element :
xml.WriteStartElement("category");
foreach(Products p in c.Products)
{
xml.WriteElementString("product", p.ProductName);
}
// Write the closing root element :
xml.WriteEndElement();
xml.Flush();
}
// CLose the helper and stream :
xml.Close();
xmlFileStream.Close();
}
}
}

Answer 1

There are multiple problems with the code being shared.
Lets try to understand each problem and think of a possible solution to the problem -
The problem statement as far as I understand is, you wanted to create a XML file with category and products under the category. So for simplicity I assume you are trying to get a XML file as below -
<?xml version="1.0" encoding="utf-8"?>
<categories>
<category>
<product>Chai</product>
<product>Chang</product>
<product>Guaraná Fantástica</product>
<product>Sasquatch Ale</product>
<product>Steeleye Stout</product>
<product>Côte de Blaye</product>
</category>
<category>
<product>Aniseed Syrup</product>
<product>Chef Anton's Cajun Seasoning</product>
<product>Chef Anton's Gumbo Mix</product>
<product>Grandma's Boysenberry Spread</product>
</category>
</categories>
Coming to what's wrong with above posted code -
Problem 1: Multiple Creation of file with the specified path -
// Create a file stream :
xmlFileStream = File.Create(path);
you have already fired File.Create in the above line so when you are firing the below code it is saying file already in use.... (the below line is not required)
await using (FileStream stream = File.Create(path))
Problem 2: Linq query is not right. You can replace your linq query with the below code -
var cats = db.Categories
.Include(c => c.Products).ToList();
Problem 3: Xml construction is wrong...
You need to wrap the category tag inside a parent as multiple category objects will get created. Also in the code above you are trying to flush the xml when one category is read. You need to perform flush once the last
xml.WriteEndElement();
is executed.
So you can replace the code block for creating xml as below -
// Write the Xml declaration :
xml.WriteStartDocument();
xml.WriteStartElement("categories");
// Serialize the object graph to the stream :
foreach (Categories c in cats)
{
// Write a root element :
xml.WriteStartElement("category");
foreach (Products p in c.Products)
{
xml.WriteElementString("product", p.ProductName);
}
// Write the closing root element :
xml.WriteEndElement();
}
xml.WriteEndElement();
xml.Flush();
// CLose the helper and stream :
xml.Close();
xmlFileStream.Close();
Now the file should get created with the categories->category[].
And each category->product[].
Thanks