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c#asp.net.netsessionsession-variables
CJe
CJe

Reputation: 1992

Session object changes when object is updated in C#

I have this really weird problem and I'm sure I'm missing something obvious here. I have these two lines:

HttpContext.Current.Session[listModelType + "ListModel"] = listModel;
listModel.ProductRows = new Collection<ProductRow>(listModel.ProductRows.Where(r => r.ParentRowId == 0).ToList());

After the second line is executed my session object is updated as well (according to "Watch" in Visual Studio)

What am I missing here?

I have tried

int i = 0;
HttpContext.Current.Session["i"] = i;
i++;

and HttpContext.Current.Session["i"] remains 0.

Upvotes: 6

Views: 8392

Answers (6)

Chandu Gunji
Chandu Gunji

Reputation: 11

In the first example your session variable is pointing to a reference so it gets updated because the two references are pointing to the same value.

so before assigning to the session you convert it into Json and then assign

HttpContext.Current.Session[listModelType + "ListModel"] = JsonConvert.SerializeObject(listModel);

Note: JsonConvert is from name space Newtonsoft.Json namespace in c#

In second line if value changes in listModel object that does't reflect session. but when you want to retreive the value from session you should convert to object form Json

if (HttpContext.Current.Session[listModelType + "ListModel"] != null)
{

    listModel = JsonConvert.DeserializeObject<*CLASS name of lsitmodel*>((string)HttpContext.Current.Session[listModelType + "ListModel"]);

}

Upvotes: 1

Chandu Gunji
Chandu Gunji

Reputation: 11

In the first example your session variable is pointing to a reference so it gets updated because the two references are pointing to the same value.

so before assigning to the session you convert it into Json and then assign

   HttpContext.Current.Session[listModelType + "ListModel"] = JsonConvert.SerializeObject(listModel);

Note: JsonConvert is from name space Newtonsoft.Json namespace in c#

In second line if value changes in listModel object that does't reflect session. but when you want to retreive the value from session you should convert to object form Json

   if (HttpContext.Current.Session[listModelType + "ListModel"] != null) {

        listModel = JsonConvert.DeserializeObject<*CLASS name of lsitmodel*>((string)HttpContext.Current.Session[listModelType + "ListModel"]);

    }

Upvotes: 0

dotnetfly
dotnetfly

Reputation: 190

The correct way should be:

  int i = 0;
  i++;
  HttpContext.Current.Session["i"] = i;

the HttpContext.Current.Session["i"] remains 1.

Upvotes: 0

Adi H
Adi H

Reputation: 738

In the first example your session variable is pointing to a reference so it gets updated because the two references are pointing to the same value.

The second session variable is pointing to a primitive (value) type so they have separate copies of value.

Upvotes: 1

Darren
Darren

Reputation: 70718

In your first example you are storing a reference to the object (The lists memory location). So if the list is updated it will reflect in the session. This is a reference type.

In the second example you are using a value type:

int i = 0;
HttpContext.Current.Session["i"] = i;
i++;

You declare i and set it to 0 (Value type)

You store the value 0 in the session. (Not the memory location of i)

You increment i but the session still has the value 0

Upvotes: 4

CodeCaster
CodeCaster

Reputation: 151586

See value types and reference types.

The int is a value type so will be stored "as-is" on the moment of assignment; your listModel is a reference type so you store a reference to the object in your session, not the value of the object.

You'll have to create a new instance of listModel if you want the one in your session untouched.

Upvotes: 12

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