CODEWITHSUNDEEP
c#
Flavio Caetano
Flavio Caetano

Reputation: 33

"Dictionary nest" in C#?

Im beginner in C# and I´m trying to do the following:

I created a Dictionary: _innerProducts = new Dictionary<string, string>();

then another dictionary to store the first one on it: _KitProducts = new Dictionary<string, Dictionary<string, string>>();

The first one (_innerProducts) contains about 15 products atributes that I collected from and .xml file, and the TKey its the product code.

after collect all the atributes I call:

_KitProducts.Add(_innerProducts["cProd"], _innerProducts);

When I watch this via debug, its works fine, as I can see:

Before Clear

The problem is that I cannot add another group of atributes using the same TKey as the first _innerProducts "cProd", so inside the foreach I put one _innerProducts.Clear(); at the end.

The problem is when I Clear it, it clear not only the current _innerProducts, it clear the TValue of the _KitProducts too:

After Clear

Im not sure if this is because of those "by reference" and not "by value" lecture that I read (remember I´m at very beginning), so what should I do in this case?

It will be a lot of those cases, I know that I will need to store it (but I still didnt learn Entity Framework, working on it), while that, Im just storing in the Dictionary to learning purposes.

Thanks and sorry for the english, isnt my main language.

Upvotes: 3

Views: 134

Answers (2)

mikka
mikka

Reputation: 176

If you wish to avoid changing your data inside the main dictionary - just put the copies of inner dictionaries

var key = _innerProducts["cProd"];
var value = new Dictionary<string, string>(_innerProducts);
_KitProducts.Add(key, value);

Upvotes: 1

Heinzi
Heinzi

Reputation: 172200

After adding the value to the outer dictionary, both _innerProducts and the value of the outer dictionary entry refer to the same object:

             +-----------------------+
             | your inner dictionary |
             +-----------------------+
                ^          ^
                |          |
      _innerProducts      value in the outer dictionary entry

When executing _innerProducts.Clear(), you empty that dictionary with the following result:

             +-----------------------+
             |    empty dictionary   |
             +-----------------------+
                ^          ^
                |          |
      _innerProducts      value in the outer dictionary entry

Thus, instead of emptying the existing instance, create a new instance, i.e., replace

_innerProducts.Clear();     // "a.DoSomething()" operates on the object referenced by a

with

_innerProducts = new Dictionary<string, string>();    // "a = ..." defines which object a refers to

That results in the following situation:

   +-----------------------+    +-----------------------+
   |   a new, empty dict.  |    | your inner dictionary |
   +-----------------------+    +-----------------------+
                         ^          ^
                         |          |
               _innerProducts      value in the outer dictionary entry

That way, you don't modify the existing inner dictionary, but instead let the variable _innerProducts point to a new one.

Even simpler and better, if possible: Move the declaration of _innerProducts inside the loop that you use to fill _KitProducts. That will ensure that each loop iteration gets its own instance of the inner dictionary.

Upvotes: 5

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