MVC Tempdata , Peek and Keep confusion

This article talks about MVC Tempdata and how MVC tempdata, Peek and Keep works using example and step by step video tutorial on mvc.

This blog assumes you have idea on MVC in case not I would suggest starting from this youtube video Learn MVC.
Recently I was taking MVC class in Mumbai and I saw there was lot of confusion among participants on how MVC tempdata , Peek and Keep works. I think the confusion stems because most of the MVC developers know only thehalf truth.
So the half thing which most of MVC developer know is:-
“Tempdata helps to preserve values for a single request”.
The other half-truth which developers do not know is or I will say which confuses developer is:-
“TempData CAN ALSO preserve values for the next request depending on 4 conditions”.
So let us try to understand the above two statements. When an end user send’s a request to a MVC application “TempData” is maintained throughout the complete request. This request can traverse through multiple actions or controllers until it displays the view on the browser.

Now in the same session (without closing the browser) if a new / second request is initiated then “TempData” will be persisted depending on 4 CONDITIONS:-

• Not Read.
• Normal Read.
• Read and Keep.
• Peek and Read.

So let’s discuss these four conditions in more detail ( Do see the below diagram for better understanding ):-
Condition 1 (Not read):- If you set a “TempData” inside your action and if you do not read it in your view then “TempData” will be persisted for the next request.
Condition 2 ( Normal Read) :- If you read the “TempData” normally like the below code it will not persist for the next request.

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stringstr = TempData[“MyData”];

Even if you are displaying it’s a normal read like the code below.

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@TempData[“MyData”];

Condition 3 (Read and Keep) :- If you read the “TempData” and call the “Keep” method it will be persisted.

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@TempData[“MyData”];
TempData.Keep(“MyData”);

Condition 4 ( Peek and Read) :- If you read “TempData” by using the “Peek” method it will persist for the next request.

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stringstr = TempData.Peek("Td").ToString();

So if you register these four condition’s in your mind you should not have any confusion’s around TempData .

List vs IEnumerable vs IQueryable vs ICollection vs IDictionary

Collection

Collection is set of related records. It includes a meaningful unit:
We should select appropriate container to store data  temporarily for fetch and modification process.
Appropriate container depends on:
1. Our aim which we want to do on data ( just reading, doing modification such as insert, delete, update )
2. Number of records which should be transferred

Array

1. Fixed Length -> Its size is not flexible. It is determined at instantiation time.

 2. Strongly Typed -> Developers determine its type at the instantiation time instead of runtime. This feature makes to run fast at runtime, since it does not need to wait for type definition.

 3. Developers use "foreach" keyword to fill and iterate through array.

Fixed Length and Strongly Typed consume less memory, therefore it has good performance.

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  //It is obvious that strArray is 
        //1. string   --> Strongly Type 
        //2. Sized=10 --> Fixed Size

        string[] strArray = new string[10];

        for (int i = 0; i < 10; i++)
        {
            if (strArray[i]==null)
            {
                strArray[i] = (i+1).ToString();
            }
        }

        this.ListBoxArray.DataSource = null;
        this.ListBoxArray.Items.Clear();

        this.ListBoxArray.DataSource = strArray;
        this.ListBoxArray.DataBind();

ArrayList

1. Arraylist is NOT Fixed Length -> It is possible that data grows. On the one hand it is a good feature whenever developers are not sure about size of arraylist and on the other hand it might take long time for size definition.

2. Arraylist is NOT Strongly Typed -> Whenever developers are not sure about what is exactly type definition for input or output data and they should wait until runtime to appear its type. Its disadvantage is time consuming at the runtime for memory to determine type definition.

3. Developers use "foreach" keyword to fill and iterate through arraylist.

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public class Product
    {
        public Product()
        {
        
        }
        public Product(string Code, string Name)
        {
            _Code = Code;
            _Name = Name;
        }

      public string _Code {get; set;}
            public string _Name { get; set; }
    }

ArrayList can accept string, integer and decimal Simultaneously.

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        //It is NOT obvious that strArrayList is 1. string? int? object? decimal?  --> NOT Strongly Type 
        //                                       2. Sized=10? 20? 100?             -->NOT Fixed Size
        // Namespace: System.Collections

        System.Collections.ArrayList strArrayList = new System.Collections.ArrayList();
        //System.Linq.IQueryable  type of data is not specific runtime defered support
        strArrayList.Add("Mahsa");  //   "Mahsa": is string
        strArrayList.Add(1);        //        1 : is integer
        strArrayList.Add(0.89);     //      0.89: is decimal  

        this.ListBoxArrayList.DataSource = null;
        this.ListBoxArrayList.Items.Clear();
        this.ListBoxArrayList.DataSource = strArrayList;
        this.ListBoxArrayList.DataBind();

        System.Text.StringBuilder str= new System.Text.StringBuilder();

        foreach (var item in strArrayList)
        {
            str.Append(" , "+item);
        }
        this.lblArrayList.Text = str.ToString();
        
        //Below is old way to fill obj from product , in Arraylist you need to create more than one instance
       // Product objProduct = new Product();
       // objProduct.Code = "1001";
       // objProduct.Name = "Chair";

        //It is NOT obvious that strArrayList is 
        //1. string? int? object? decimal? OR OBJECT??  --> NOT Strongly Type 
        //2. Sized=10? 20? 100?                         -->NOT Fixed Size
        // Namespace: System.Collections

        System.Collections.ArrayList objArrayList = new System.Collections.ArrayList();

        objArrayList.Add(new Product("1001", "Chair"));
        objArrayList.Add(new Product("1002", "Sofa"));
        objArrayList.Add(new Product("1003", "Carpet"));

        this.DropDownListArrayListObject.DataSource = null;
        this.DropDownListArrayListObject.Items.Clear();
        this.DropDownListArrayListObject.DataSource = objArrayList;

        //* Finding among Object of Array List is difficult , you have to find your specific item by index
        Product objTemp = (Product)objArrayList[0];
        objArrayList.Remove(objTemp);
        //*
        this.DropDownListArrayListObject.DataTextField = "_Name";
        this.DropDownListArrayListObject.DataValueField = "_Code";
        this.DropDownListArrayListObject.DataBind();
        this.GridViewArrayListObject.DataSource = objArrayList;
        this.GridViewArrayListObject.DataBind();

HashTable

HashTable is another kind of data structure that defines key value for each data section. Therefore finding data is easy just by point out to its key. It is NOT strongly typed and NOT fixed size.

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 //It is NOT obvious that strArrayList is 
        //1. string? int? object? decimal? OR OBJECT??  --> NOT Strongly Type 
        //2. Sized=10? 20? 100?                         -->NOT Fixed Size
        // Namespace: System.Collections
        //Hashtable solve the problem in Arraylist when we are looking for specific item
        //Hashtable dedicate a key for each item, then finding item is easier and faster 

         System.Collections.Hashtable objHashTable = new System.Collections.Hashtable();
       
         objHashTable.Add("1001","Chair");
         objHashTable.Add("1002", "Sofa");
         objHashTable.Add("1003", "Carpet");

     
        this.DropDownListHashTable.DataSource = null;
        this.DropDownListHashTable.Items.Clear();
        this.DropDownListHashTable.DataSource = objHashTable;
        //* finding item is easier you just need to point to it by call its key 
        objHashTable.Remove("1002");
        //*
        this.DropDownListHashTable.DataTextField = "Value";
        this.DropDownListHashTable.DataValueField = "Key";
        this.DropDownListHashTable.DataBind();

Stack

We have different data structure and stack is one of them. Stack is subset of data structure. Stack is prioritized data structure (such as List is indexed base). Stack defines priority for each item, it means stack behavior force its items to put (push) inside stack prioritized form. So stack put later item on the top of items and this behavior is "defining priority for each item". Therefore whenever you want to insert item, you should add (PUSH) it at the top of the stack and whenever you want to remove (POP) item from stack you should remove it from top of the stack. As you got it, item that comes last one will be selected to POP for first one and its expression in computer science is equal to "Last in First out" == "LIFO".

It is NOT strongly typed and NOT fixed size.

Stack - Push

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 //Stack is LIFO: Last in First Out
        System.Collections.Stack objStackPush = new System.Collections.Stack();

        //By Push method you can insert item at the top of the stack
        objStackPush.Push("Mahsa");
        objStackPush.Push("Hassankashi");
        this.lblPop.Text = "";
        this.ListBoxStack.DataSource = objStackPush.ToArray();
        this.ListBoxStack.DataBind();

Stack - Pop

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          System.Collections.Stack objStackPop = new System.Collections.Stack();

        objStackPop.Push("Mahsa");
        objStackPop.Push("Hassankashi");

        //By Pop method you can remove item from the top of the stack --> Last in First in 
        this.lblPop.Text = objStackPop.Pop().ToString();

        this.ListBoxStack.DataSource = objStackPop.ToArray();
        this.ListBoxStack.DataBind();

Queue

Queue is another kind of data structure that defines priority for each item in other form. Therefore whenever you want to insert item, you should add (Enqueue) it at the head of the queue and whenever you want to remove (Dequeue) item from queue you should remove it from bottom of the queue. As you got it, item that comes first one will be selected to Dequeue for first one and its expression in computer science is equal to "First in First out" == "FIFO".

It is NOT strongly typed and NOT fixed size.

Queue - Enqueue

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         //Queue is FIFO: First in First Out
        System.Collections.Queue objQueue = new System.Collections.Queue();

        //By Enqueue method you can insert item at the END of the Queue
        objQueue.Enqueue("Mahsa");
        objQueue.Enqueue("Hassankashi");
        objQueue.Enqueue("Cosmic");
        objQueue.Enqueue("Verse");

        this.lblQueue.Text = "";
        this.ListBoxQueue.DataSource = objQueue.ToArray();
        this.ListBoxQueue.DataBind();

Queue - Dequeue

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          System.Collections.Queue objQueue = new System.Collections.Queue();

        objQueue.Enqueue("Mahsa");
        objQueue.Enqueue("Hassankashi");
        objQueue.Enqueue("Cosmic");
        objQueue.Enqueue("Verse");

        //By Dequeue method you can remove item from the BEGINING of the Queue --> First in First out FIFO
        this.lblQueue.Text=objQueue.Dequeue().ToString();
       
        this.ListBoxQueue.DataSource = objQueue.ToArray();
        this.ListBoxQueue.DataBind();

List

Why we need List?

1. List is NOT Fixed Length -> It is possible that data grows. On the one hand it is a good feature whenever developers are not sure about size of arraylist and on the other hand it might take long time for size definition.

2. List is Strongly Typed when it is defined "Generic" -> Whenever developers are sure about what is exactly type definition for input or output data and they do not wait until runtime to appear its type. This feature makes to run fast at runtime, since it does not need to wait for type definition. 

3. Developers use "foreach" keyword to fill and iterate through array.

Since List is not Fixed Length makes developers feel flexible to use it, and because of it is Strongly Typed when it is defined "Generic" so our code runs fast at runtime because it does not need to wait for type definition.

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        //Like Array is Strong Type
        //Like ArrayList with No Dimension
        System.Collections.Generic.List<string> strList = new List<string>();


        strList.Add("Mahsa");
        strList.Add("Hassankashi");
        strList.Add("Cosmic");
        strList.Add("Verse");
       
        this.ListBoxListGeneric.DataSource = strList;
        this.ListBoxListGeneric.DataBind();

        System.Text.StringBuilder str = new System.Text.StringBuilder();

        foreach (var item in strList)
        {
            str.Append(" , " + item);
        }
        this.lblList.Text = str.ToString();

IList

Why we need IList? IList is implemented by List, Ilist is an interface and implements methods. Whenever you estimate probability that your code would be changed in future you have to use IList because interface reduces dependency and with the little modification your code runs. Therefore you should observe polymorphism in order to decouple your app and control on adding or removing method that might be changed. Everything else is similar. Whenever we want to change on some operation, so “IList” allow us to do that easily with at least changing in the whole of codes. 

Interfaces can not be instantiate, so it should be instantiate from List

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System.Collections.Generic.IList<string> strIList = new List<string>();

Difference between Concrete Class and Interface

1. Concrete Class inherits from just ONE class but it Can implements one or MORE than one interfaces

2. You can write inside concrete class full version of your function while you have to define just signature inside the interface.

3. You can define variable and value Inside Concrete Class while you are not allowed to define variable inside interfaces.

4. An Concrete class can have constructor while you are not allowed to define constructor inside interfaces.

5. Abstract class can containe access modifier while intefaces does not.

As I mentioned that how a class cannot be driven from two class it just can be driven from only one class, so whenever you want to drive from two class it is not possible to inherit from two abstract class but it is possible to drive from more than one class by interfaces.

Later in future if developers decide to add some features on their class and inherit it from another class, developers always prefer to use interface of collection so that if you want to change your code and enhance its abilities, choose interfaces.

On the other hand interface keeps your program extensible and Decouple: The classes are independent from each other, so error, exception and failure will happen rarely in future changing code by interfaces.

Polymorphism: When you are using interface you absolutely observe and do polymorphism and oop. It means encapsulate your designer. Interface means a point or a node to join two part to each other it means making low dependency from two part and make a joint section to make flexible change in future.

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        //Ilist can not be instantiate from Ilist , so it should be instantiate from List
        System.Collections.Generic.IList<string> strIList = new List<string>();

        strIList.Add("Mahsa");
        strIList.Add("Hassankashi");
        strIList.Add("Cosmic");
        strIList.Add("Verse");

        
        this.ListBoxListGeneric.DataSource = strIList;
        this.ListBoxListGeneric.DataBind();

        System.Text.StringBuilder str = new System.Text.StringBuilder();

        foreach (var item in strIList)
        {
            str.Append(" , " + item);
        }
        this.lblList.Text = str.ToString();

IEnumerable

IEnumerable is suitable just for iterate through collection and you can not modify (Add or Remove) data IEnumerable bring ALL data from server to client then filter them, assume that you have a lot of records so IEnumerable puts overhead on your memory.

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 //IEnumerable can not be instantiate from Enumerable , so it should be instantiate from List
        System.Collections.Generic.IEnumerable<Employee> empIEnumerable = new List<Employee>
        {   new Employee { ID = 1001, Name="Mahsa"},
            new Employee { ID = 1002, Name = "Hassankashi" },
            new Employee { ID = 1003, Name = "CosmicVerse" },
            new Employee { ID = 1004, Name = "Technical" }
        };


        this.GridViewIEnumerable.DataSource = empIEnumerable;
        this.GridViewIEnumerable.DataBind();

        System.Text.StringBuilder str = new System.Text.StringBuilder();

        foreach (Employee item in empIEnumerable)
        {
            str.Append(" , " + item.ID +"-"+item.Name);
        }

        this.lblIEnumerable.Text = str.ToString();

IQueryable

Whenever we encounter to huge data with so many records so we have to reduce overhead from application. IQueryable prepares high performance in such situations (huge data) by filtering data firstly and then sending filtered data to client.

Follow "Entity Framework DatabaseFirst" from this article for making DBContext

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DataAccessEntities ctx = new DataAccessEntities();
        var ctx = new DataAccessEntities();
    

Data Access

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//Difference between IQueryable and IEnumerable

        //You can instantiate IEnumerable from List

        IEnumerable<employee> queryIEnumerable = new List<employee>() ;


        //Bring  ALL records from server --> to client then filter collection
       //To bring all data from server you should omit where cluse from linq to sql 
        queryIEnumerable = from m in ctx.Employees select m;

        //If you use where as extension method with IEnumerable then All records will be loaded 
        queryIEnumerable = queryIEnumerable.Where(x => x.ID == 1).ToList();
       


        //You can not instantiate IQueryable

        IQueryable<employee> queryIQueryable=null;

        //Bring just ONE record from server --> to client

        queryIQueryable = (from m in ctx.Employees
                     where m.ID == 1
                     select m);

        //Whenever you call IQueryable so ==> It will be executed 
        this.GridViewIQueryable.DataSource = queryIQueryable.ToList();
        this.GridViewIQueryable.DataBind();
</employee></employee></employee>

SQL Profiler:

How to trace your query generates TSQL & How many records will be loaded:

Step 1:

Start -> MS SQL Server 2008 -> Performance Tools -> SQL Server Profiler

 

Step 2:

SQL Server Profiler -> File -> New Trace

Step 3:

Connect with you user name and password.

Step 4:

General (Tab) -> Use the Template: Standard

Step 5:

Event Selection (Tab) -> Event : TSQL -> Select : SQL-BatchCompleted | Select Show all Columns

Press Column Filter -> Database Name: Like: "DataAccess" 

Press Run

Step 6:

Go To MS SQL Server Management Studio -> Count all of records (records=5)

Step 7:

IEnumerable generates:

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SELECT 
[Extent1].[ID] AS [ID], 
[Extent1].[Name] AS [Name], 
[Extent1].[Age] AS [Age]
FROM [dbo].[Employee] AS [Extent1]

IQueryable generates:

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SELECT 
[Extent1].[ID] AS [ID], 
[Extent1].[Name] AS [Name], 
[Extent1].[Age] AS [Age]
FROM [dbo].[Employee] AS [Extent1]
WHERE 1 = [Extent1].[ID]

ICollection

ICollection inherits from IEnumerable. There is one difference:

you can find IEnumerable[ i ] --> Index Based

you can NOT find ICollection[ i ] --> Not Index Based

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         //IList {indexer and Modify} vs ICollection {randomly and Modify}         
        //Collection can not be instantiate from ICollection , so it should be instantiate from List
        System.Collections.Generic.ICollection<string> strICollection = new List<string>();
        strICollection.Add("Mahsa");
        strICollection.Add("Hassankashi");

        //Countable***
        int ICollectionCount=strICollection.Count;

        this.ListBoxICollection.DataSource = strICollection;
        this.ListBoxICollection.DataBind();
        System.Text.StringBuilder str = new System.Text.StringBuilder();
        foreach (var item in strICollection)
        {
            str.Append(" , " + item);
        }
        this.lblICollection.Text = str.ToString();
        
        //IList***
        System.Collections.Generic.IList<Employee> objIList = new List<Employee>();
        objIList = (from m in ctx.Employees
                    select m).ToList();
       
       Employee obj = objIList.Where(i => i.Name == "Sara").FirstOrDefault();
       int indexofSara= objIList.IndexOf(obj);
       int cIList = objIList.Count;

        //ICollection***
        System.Collections.Generic.ICollection<Employee> objICollection = new List<Employee>();
        objICollection = (from m in ctx.Employees
                          select m).ToList();
        Employee objIC = objICollection.Where(i => i.Name == "Sara").FirstOrDefault();
        //You can not get index of object , if you clear comment from below code appears error
       // int indexofSaraICollection = objIC.IndexOf(objIC);
        int cICollection = objICollection.Count;

Stack Generic

Push:

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//Stack is LIFO: Last in First Out
       //Here is for Push Stack in Generic
       //System.Collections.Stack objStackPush = new System.Collections.Stack();
       //Stack<T> can be instantiated from Stack<T>

       System.Collections.Generic.Stack<int> objStackPush = new System.Collections.Generic.Stack<int>();

       objStackPush.Push(1);
       objStackPush.Push(2);

       this.lblPopGeneric.Text = "";
       this.ListBoxStackGeneric.DataSource = objStackPush.ToArray();
       this.ListBoxStackGeneric.DataBind();

Pop:

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//Stack is LIFO: Last in First Out
       //Here is for Pop Stack in Generic
       //System.Collections.Stack objStackPop = new System.Collections.Stack();
       //Stack<T> can be instantiated from Stack<T>

       System.Collections.Generic.Stack<int> objStackPop = new System.Collections.Generic.Stack<int>();

       objStackPop.Push(1);
       objStackPop.Push(2);

       this.lblPop.Text = objStackPop.Pop().ToString();
       this.ListBoxStack.DataSource = objStackPop.ToArray();
       this.ListBoxStack.DataBind();

Queue Generic

Enqueue:

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//Queue is FIFO: First in First Out
       //Here is for Enqueue Queue in Generic
       //System.Collections.Queue objQueue = new System.Collections.Queue();
       //Queue<T> can be instantiated from Queue<T>

       System.Collections.Generic.Queue<int> objQueue = new System.Collections.Generic.Queue<int>();
       objQueue.Enqueue(1);
       objQueue.Enqueue(2);

       this.lblQueue.Text = "";

       this.ListBoxQueue.DataSource = objQueue.ToArray();
       this.ListBoxQueue.DataBind();

Dequeue:

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//Queue is FIFO: First in First Out
        //Here is for Dequeue Queue in Generic
        //System.Collections.Queue objQueue = new System.Collections.Queue();
        //Queue<T> can be instantiated from Queue<T>

        System.Collections.Generic.Queue<int> objQueue = new System.Collections.Generic.Queue<int>();

        objQueue.Enqueue(1);
        objQueue.Enqueue(2);

        this.lblQueue.Text = objQueue.Dequeue().ToString();

        this.ListBoxQueue.DataSource = objQueue.ToArray();
        this.ListBoxQueue.DataBind();

 

Dictionary and IDictionary

Dictionary is GENERIC while HashTable is not generic : Dictionary<TKey, TValue>, There is a tiny difference between them that if dictionary can not find specific key will throw an exception while HashTable just returns null.

IDictionary is interface and if you estimate big changes in future use IDictionary instead of Dictionary.

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        //Dictionary can instantiate from Dictionary , Dictionary is similar to Hashtable, 
        //Dictionary is GENERIC but Hashtable is NON GENERIC
        //Such Hashtable you can find object by its key
        System.Collections.Generic.Dictionary<int, string=""> objDictionary = new Dictionary<int, string="">();

        objDictionary.Add(1001, "Mahsa");
        objDictionary.Add(1002, "Hassankashi");
        objDictionary.Add(1003, "Cosmicverse");

        string str = objDictionary[1002];

        this.ListBoxDictionary.DataSource = objDictionary;
        this.ListBoxDictionary.DataBind();</int,></int,>